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+The Project Gutenberg eBook, The Variation of Animals and Plants Under
+Domestication, Volume II (of 2), by Charles Darwin
+
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+
+
+
+Title: The Variation of Animals and Plants Under Domestication, Volume II (of 2)
+
+
+Author: Charles Darwin
+
+
+
+Release Date: May 20, 2009  [eBook #28897]
+
+Language: English
+
+Character set encoding: ISO-646-US (US-ASCII)
+
+
+***START OF THE PROJECT GUTENBERG EBOOK THE VARIATION OF ANIMALS AND
+PLANTS UNDER DOMESTICATION, VOLUME II (OF 2)***
+
+
+E-text prepared by Steven Gibbs, Keith Edkins, and the Project Gutenberg
+Online Distributed Proofreading Team (http://www.pgdp.net)
+
+
+
+Transcriber's note:
+
+   A few typographical errors have been corrected: they are listed
+   at the end of the text. The Errata on page viii, which were in
+   the original book, have been applied to this e-text.
+
+   Page numbers within curly brackets (such as {iii} and {27}
+   have been included so that the reader might use the index.
+
+
+
+
+
+THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.
+
+by
+
+CHARLES DARWIN, M.A., F.R.S., &c.
+
+IN TWO VOLUMES.--VOL. II.
+
+With Illustrations.
+
+
+
+
+
+
+
+LONDON:
+John Murray, Albemarle Street.
+1868.
+
+The right of Translation is reserved.
+
+London: Printed by William Clowes and Sons, Stamford Street, and Charing
+Cross.
+
+
+
+
+{iii}
+
+CONTENTS OF VOLUME II.
+
+CHAPTER XII.
+
+INHERITANCE.
+
+WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATED
+ANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERS
+INHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE INHERITED--DISEASES
+IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL DEVIATIONS OF
+STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER
+AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED
+PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS,
+COLOUR OF FRUIT AND FLOWERS, COLOUR OF HORSES--NON-INHERITANCE IN CERTAIN
+CASES--INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS
+OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION
+... Page 1
+
+CHAPTER XIII.
+
+INHERITANCE _continued_--REVERSION OR ATAVISM.
+
+DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS,
+FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERAL
+ANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSION
+THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--IN
+DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING A
+DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHER
+PROXIMATE CAUSES OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL
+CHARACTERS--UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE
+WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALL
+ITS LATENT CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS
+DUE IN SOME CASES TO REVERSION ... Page 28
+
+CHAPTER XIV.
+
+INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL
+LIMITATION--CORRESPONDENCE OF AGE.
+
+FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF
+INHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY,
+IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER;
+SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED
+AND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIRED
+CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE,
+SOMETIMES LOST BY ONE SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OF
+LIFE--THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS
+EXHIBITED IN DOMESTICATED ANIMALS; AS EXHIBITED IN THE APPEARANCE AND
+DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THE
+CHILD THAN IN THE PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS ... Page
+62
+
+{iv}
+
+CHAPTER XV.
+
+ON CROSSING.
+
+FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN
+THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE
+OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY
+THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS
+OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS
+INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLY
+APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES, AND THE
+FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE BRED TRUE FROM
+THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT SPECIES IN RELATION TO
+THE FORMATION OF DOMESTIC RACES ... Page 85
+
+CHAPTER XVI.
+
+CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OF
+DOMESTICATION ON FERTILITY.
+
+DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS
+CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL
+PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES
+OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN
+SOME DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TO
+STERILITY NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OF
+UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION ... Page
+100
+
+CHAPTER XVII.
+
+ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
+INTERBREEDING.
+
+DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID
+TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING, AND
+ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED;
+HALF-WILD CATTLE LONG KEPT IN THE SAME
+PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS
+ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS,
+GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS,
+FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZE
+OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTS
+WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE,
+BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS
+EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION ... Page 114
+
+{v}
+
+CHAPTER XVIII.
+
+ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:
+STERILITY FROM VARIOUS CAUSES.
+
+ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF
+LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE
+COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF SECONDARY
+SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OF
+DOMESTICATED ANIMALS FROM CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OF
+INDIVIDUAL ANIMALS--STERILITY OF PLANTS FROM CHANGED CONDITIONS OF
+LIFE--CONTABESCENCE OF THE ANTHERS--MONSTROSITIES AS A CAUSE OF
+STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE
+DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY
+BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS
+FRUIT ... Page 145
+
+CHAPTER XIX.
+
+SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.
+
+ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON
+FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED
+CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE
+DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS
+WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE
+PROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS--STERILITY OF CROSSED SPECIES
+DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATED
+THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY
+STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY
+BETWEEN CROSSED SPECIES AND CROSSED VARIETIES--CONCLUSION ... Page 173
+
+CHAPTER XX.
+
+SELECTION BY MAN.
+
+SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL
+SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN
+SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS, AND
+BY SEMI-CIVILISED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED
+TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR
+DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS
+SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTS
+AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THE
+GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN ... Page 192
+
+{vi}
+
+CHAPTER XXI.
+
+SELECTION--_continued._
+
+NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH
+APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE
+TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE
+CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION
+OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION
+IS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO
+DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO
+AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO
+CONVERGENCE--CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH
+THEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF
+INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT
+TO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH
+DOMESTIC RACES HAVE ORIGINATED--SUMMARY ... Page 224
+
+CHAPTER XXII.
+
+CAUSES OF VARIABILITY.
+
+VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY
+VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO
+CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD,
+EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE
+VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO
+CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
+INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
+VARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW
+CHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM
+REVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER
+DIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY
+... Page 250
+
+CHAPTER XXIII.
+
+DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.
+
+SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
+CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE
+TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR
+FOOD, ETC.--PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE
+INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A
+STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL
+CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS OF
+PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT
+INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF
+VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF
+CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
+UNNATURAL TREATMENT--SUMMARY ... Page 271
+
+{vii}
+
+CHAPTER XXIV.
+
+LAWS OF VARIATION--USE AND DISUSE, ETC.
+
+NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE
+EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF
+LIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH
+THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS ... Page
+293
+
+CHAPTER XXV.
+
+LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY.
+
+EXPLANATION OF TERM--CORRELATION AS CONNECTED WITH
+DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE
+OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS
+ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE HEAD AND THE
+EXTREMITIES--BETWEEN THE SKIN AND DERMAL APPENDAGES--BETWEEN THE ORGANS OF
+SIGHT AND HEARING--CORRELATED MODIFICATIONS IN THE ORGANS OF
+PLANTS--CORRELATED MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND
+EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTH
+COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS
+CORRELATED WITH CONSTITUTIONAL PECULIARITIES ... Page 319
+
+CHAPTER XXVI.
+
+LAWS OF VARIATION, _continued_--SUMMARY.
+
+ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OF
+MULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICAL
+PRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THE
+PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS OR
+PARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS ... Page 339
+
+CHAPTER XXVII.
+
+PROVISIONAL HYPOTHESIS OF PANGENESIS.
+
+PRELIMINARY REMARKS--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE
+POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE DIRECT ACTION
+OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE FUNCTIONAL INDEPENDENCE
+OF THE ELEMENTS OR UNITS OF THE BODY--VARIABILITY--INHERITANCE--REVERSION.
+
+SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY
+ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE
+SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION ... Page
+357
+
+{viii}
+
+CHAPTER XXVIII.
+
+CONCLUDING REMARKS.
+
+DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND
+DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO
+SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH
+PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED ... Page 405
+
+INDEX ... Page 433
+
+       *       *       *       *       *
+
+ERRATA.
+
+  Vol. II., pp. 18, 232, 258, for Crataegus oxycantha, read oxyacantha.
+       ,,   p.  98, 8 lines from top, for Dianthus armoria read armeria.
+       ,,   ,,  156, 15 lines from bottom, for Casuarinus read Casuarius.
+       ,,   ,,   ,,  4 lines from bottom, for Grus cineria read cinerea.
+       ,,   ,,  168, 11 lines from top, for Oesculus read Aesculus.
+       ,,   ,,  300, 3 lines from top, for anastomising read anastomosing.
+       ,,   ,,   ,,  foot-note, for Birckell read Brickell.
+
+       *       *       *       *       *
+
+
+{1} THE
+
+VARIATION OF ANIMALS AND PLANTS
+
+UNDER DOMESTICATION.
+
+       *       *       *       *       *
+
+CHAPTER XII.
+
+INHERITANCE.
+
+    WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATED
+    ANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERS
+    INHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE
+    INHERITED--DISEASES IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL
+    DEVIATIONS OF STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY
+    DIGITS AFTER AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED
+    FROM NON-AFFECTED PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING
+    TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS, COLOUR OF
+    HORSES--NON-INHERITANCE IN CERTAIN CASES--INHERITANCE OF STRUCTURE AND
+    HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY
+    RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION.
+
+The subject of inheritance is an immense one, and has been treated by many
+authors. One work alone, 'De l'Heredite Naturelle,' by Dr. Prosper Lucas,
+runs to the length of 1562 pages. We must confine ourselves to certain
+points which have an important bearing on the general subject of variation,
+both with domestic and natural productions. It is obvious that a variation
+which is not inherited throws no light on the derivation of species, nor is
+of any service to man, except in the case of perennial plants, which can be
+propagated by buds.
+
+If animals and plants had never been domesticated, and wild ones alone had
+been observed, we should probably never have heard the saying, that "like
+begets like." The proposition would have been as self-evident, as that all
+the buds on the same tree are alike, though neither proposition is strictly
+true. For, as has often been remarked, probably no two individuals are {2}
+identically the same. All wild animals recognise each other, which shows
+that there is some difference between them; and when the eye is well
+practised, the shepherd knows each sheep, and man can distinguish a
+fellow-man out of millions on millions of other men. Some authors have gone
+so far as to maintain that the production of slight differences is as much
+a necessary function of the powers of generation, as the production of
+offspring like their parents. This view, as we shall see in a future
+chapter, is not theoretically probable, though practically it holds good.
+The saying that "like begets like" has in fact arisen from the perfect
+confidence felt by breeders, that a superior or inferior animal will
+generally reproduce its kind; but this very superiority or inferiority
+shows that the individual in question has departed slightly from its type.
+
+The whole subject of inheritance is wonderful. When a new character arises,
+whatever its nature may be, it generally tends to be inherited, at least in
+a temporary and sometimes in a most persistent manner. What can be more
+wonderful than that some trifling peculiarity, not primordially attached to
+the species, should be transmitted through the male or female sexual cells,
+which are so minute as not to be visible to the naked eye, and afterwards
+through the incessant changes of a long course of development, undergone
+either in the womb or in the egg, and ultimately appear in the offspring
+when mature, or even when quite old, as in the case of certain diseases? Or
+again, what can be more wonderful than the well-ascertained fact that the
+minute ovule of a good milking cow will produce a male, from whom a cell,
+in union with an ovule, will produce a female, and she, when mature, will
+have large mammary glands, yielding an abundant supply of milk, and even
+milk of a particular quality? Nevertheless, the real subject of surprise
+is, as Sir H. Holland has well remarked,[1] not that a character should be
+inherited, but that any should ever fail to be inherited. In a future
+chapter, devoted to an hypothesis which I have termed pangenesis, an
+attempt will be made to show the means by which characters of all kinds are
+transmitted from generation to generation.
+
+{3}
+
+Some writers,[2] who have not attended to natural history, have attempted
+to show that the force of inheritance has been much exaggerated. The
+breeders of animals would smile at such simplicity; and if they
+condescended to make any answer, might ask what would be the chance of
+winning a prize if two inferior animals were paired together? They might
+ask whether the half-wild Arabs were led by theoretical notions to keep
+pedigrees of their horses? Why have pedigrees been scrupulously kept and
+published of the Shorthorn cattle, and more recently of the Hereford breed?
+Is it an illusion that these recently improved animals safely transmit
+their excellent qualities even when crossed with other breeds? have the
+Shorthorns, without good reason, been purchased at immense prices and
+exported to almost every quarter of the globe, a thousand guineas having
+been given for a bull? With greyhounds pedigrees have likewise been kept,
+and the names of such dogs, as Snowball, Major, &c., are as well known to
+coursers as those of Eclipse and Herod on the turf. Even with the Gamecock
+pedigrees of famous strains were formerly kept, and extended back for a
+century. With pigs, the Yorkshire and Cumberland breeders "preserve and
+print pedigrees;" and to show how such highly-bred animals are valued, I
+may mention that Mr. Brown, who won all the first prizes for small breeds
+at Birmingham in 1850, sold a young sow and boar of his breed to Lord Ducie
+for 43 guineas; the sow alone was afterwards sold to the Rev. F. Thursby
+for 65 guineas; who writes, "she paid me very well, having sold her produce
+for 300_l_., and having now four breeding sows from her."[3] Hard cash paid
+down, over and over again, is an excellent test of inherited superiority.
+In fact, the whole art of breeding, from which such great results have been
+attained during the present century, depends on the inheritance of each
+small {4} detail of structure. But inheritance is not certain; for if it
+were, the breeder's art[4] would be reduced to a certainty, and there would
+be little scope left for all that skill and perseverance shown by the men
+who have left an enduring monument of their success in the present state of
+our domesticated animals.
+
+It is hardly possible, within a moderate compass, to impress on the mind of
+those who have not attended to the subject, the full conviction of the
+force of inheritance which is slowly acquired by rearing animals, by
+studying the many treatises which have been published on the various
+domestic animals, and by conversing with breeders. I will select a few
+facts of the kind, which, as far as I can judge, have most influenced my
+own mind. With man and the domestic animals, certain peculiarities have
+appeared in an individual, at rare intervals, or only once or twice in the
+history of the world, but have reappeared in several of the children and
+grandchildren. Thus Lambert, "the porcupine-man," whose skin was thickly
+covered with warty projections, which were periodically moulted, had all
+his six children and two grandsons similarly affected.[5] The face and body
+being covered with long hair, accompanied by deficient teeth (to which I
+shall hereafter refer), occurred in three successive generations in a
+Siamese family; but this case is not unique, as a woman[6] with a
+completely hairy face was exhibited in London in 1663, and another instance
+has recently occurred. Colonel Hallam[7] has described a race of two-legged
+pigs, "the hinder extremities being entirely wanting;" and this deficiency
+was transmitted through three generations. In fact, all races presenting
+any remarkable peculiarity, such as solid-hoofed swine, Mauchamp sheep,
+niata cattle, &c., are instances of the long-continued inheritance of rare
+deviations of structure.
+
+When we reflect that certain extraordinary peculiarities have {5} thus
+appeared in a single individual out of many millions, all exposed in the
+same country to the same general conditions of life, and, again, that the
+same extraordinary peculiarity has sometimes appeared in individuals living
+under widely different conditions of life, we are driven to conclude that
+such peculiarities are not directly due to the action of the surrounding
+conditions, but to unknown laws acting on the organisation or constitution
+of the individual;--that their production stands in hardly closer relation
+to the conditions than does life itself. If this be so, and the occurrence
+of the same unusual character in the child and parent cannot be attributed
+to both having been exposed to the same unusual conditions, then the
+following problem is worth consideration, as showing that the result cannot
+be due, as some authors have supposed, to mere coincidence, but must be
+consequent on the members of the same family inheriting something in common
+in their constitution. Let it be assumed that, in a large population, a
+particular affection occurs on an average in one out of a million, so that
+the _a priori_ chance that an individual taken at random will be so
+affected is only one in a million. Let the population consist of sixty
+millions, composed, we will assume, of ten million families, each
+containing six members. On these data, Professor Stokes has calculated for
+me that the odds will be no less than 8333 millions to 1 that in the ten
+million families there will not be even a single family in which one parent
+and two children will be affected by the peculiarity in question. But
+numerous cases could be given, in which several children have been affected
+by the same rare peculiarity with one of their parents; and in this case,
+more especially if the grandchildren be included in the calculation, the
+odds against mere coincidence become something prodigious, almost beyond
+enumeration.
+
+In some respects the evidence of inheritance is more striking when we
+consider the reappearance of trifling peculiarities. Dr. Hodgkin formerly
+told me of an English family in which, for many generations, some members
+had a single lock differently coloured from the rest of the hair. I knew an
+Irish gentleman, who, on the right side of his head, had a small white lock
+in the midst of his dark hair: he assured me that his grandmother had {6} a
+similar lock on the same side, and his mother on the opposite side. But it
+is superfluous to give instances; every shade of expression, which may
+often be seen alike in parents and children, tells the same story. On what
+a curious combination of corporeal structure, mental character, and
+training, must handwriting depend! yet every one must have noted the
+occasional close similarity of the handwriting in father and son, although
+the father had not taught his son. A great collector of franks assured me
+that in his collection there were several franks of father and son hardly
+distinguishable except by their dates. Hofacker, in Germany, remarks on the
+inheritance of handwriting; and it has even been asserted that English boys
+when taught to write in France naturally cling to their English manner of
+writing.[8] Gait, gestures, voice, and general bearing are all inherited,
+as the illustrious Hunter and Sir A. Carlisle have insisted.[9] My father
+communicated to me two or three striking instances, in one of which a man
+died during the early infancy of his son, and my father, who did not see
+this son until grown up and out of health, declared that it seemed to him
+as if his old friend had risen from the grave, with all his highly peculiar
+habits and manners. Peculiar manners pass into tricks, and several
+instances could be given of their inheritance; as in the case, often
+quoted, of the father who generally slept on his back, with his right leg
+crossed over the left, and whose daughter, whilst an infant in the cradle,
+followed exactly the same habit, though an attempt was made to cure
+her.[10] I will give one instance which has fallen under my own
+observation, and which is curious from being a trick associated with a
+peculiar state of mind, namely, pleasurable emotion. A boy had the singular
+habit, when pleased, of rapidly moving his fingers parallel to each other,
+and, when much excited, of raising both hands, with the fingers still
+moving, to the sides of his face on a level with the eyes; this boy, when
+almost an old man, could still hardly resist this trick when much pleased,
+but from its absurdity concealed it. He had eight children. Of these, a
+girl, when {7} pleased, at the age of four and a half years, moved her
+fingers in exactly the same way, and what is still odder, when much
+excited, the raised both her hands, with her fingers still moving, to the
+sides of her face, in exactly the same manner as her father had done, and
+sometimes even still continued to do when alone. I never heard of any one
+excepting this one man and his little daughter who had this strange habit;
+and certainly imitation was in this instance out of the question.
+
+Some writers have doubted whether those complex mental attributes, on which
+genius and talent depend, are inherited, even when both parents are thus
+endowed. But he who will read Mr. Galton's able paper[11] on hereditary
+talent will have his doubts allayed.
+
+Unfortunately it matters not, as far as inheritance is concerned, how
+injurious a quality or structure may be if compatible with life. No one can
+read the many treatises[12] on hereditary disease and doubt this. The
+ancients were strongly of this opinion, or, as Ranchin expresses it, _Omnes
+Graeci, Arabes, et Latini in eo consentiunt_. A long catalogue could be
+given of all sorts of inherited malformations and of predisposition to
+various diseases. With gout, fifty per cent. of the cases observed in
+hospital practice are, according to Dr. Garrod, inherited, and a greater
+percentage in private practice. Every one knows how often insanity runs in
+families, and some of the cases given by Mr. Sedgwick are awful,--as of a
+surgeon, whose brother, father, and four paternal uncles were all insane,
+the latter dying by suicide; of a Jew, whose father, mother, and six
+brothers and sisters were all mad; and in some other cases several members
+of the same family, during three or four successive generations, have
+committed suicide. Striking instances {8} have been recorded of epilepsy,
+consumption, asthma, stone in the bladder, cancer, profuse bleeding from
+the slightest injuries, of the mother not giving milk, and of bad
+parturition being inherited. In this latter respect I may mention an odd
+case given by a good observer,[13] in which the fault lay in the offspring,
+and not in the mother: in a part of Yorkshire the farmers continued to
+select cattle with large hind-quarters, until they made a strain called
+"Dutch-buttocked," and "the monstrous size of the buttocks of the calf was
+frequently fatal to the cow, and numbers of cows were annually lost in
+calving."
+
+    Instead of giving numerous details on various inherited malformations
+    and diseases, I will confine myself to one organ, that which is the
+    most complex, delicate, and probably best-known in the human frame,
+    namely, the eye, with its accessory parts. To begin with the latter: I
+    have heard of a family in which parents and children were affected by
+    drooping eyelids, in so peculiar a manner, that they could not see
+    without throwing their heads backwards; and Sir A. Carlisle[14]
+    specifies a pendulous fold to the eyelids as inherited. "In a family,"
+    says Sir H. Holland,[15] "where the father had a singular elongation of
+    the upper eyelid, seven or eight children were born with the same
+    deformity; two or three other children having it not." Many persons, as
+    I year from Mr. Paget, have two or three of the hairs in their eyebrows
+    (apparently corresponding with the vibrissae of the lower animals) much
+    longer than the others; and even so trifling a peculiarity as this
+    certainly runs in families.
+
+    With respect to the eye itself, the highest authority in England, Mr.
+    Bowman, has been so kind as to give me the following remarks on certain
+    inherited imperfections. First, hypermetropia, or morbidly long sight:
+    in this affection, the organ, instead of being spherical, is too flat
+    from front to back, and is often altogether too small, so that the
+    retina is brought too forward for the focus of the humours;
+    consequently a convex glass is required for clear vision of near
+    objects, and frequently even of distant ones. This state occurs
+    congenitally, or at a very early age, often in several children of the
+    same family, where one of the parents has presented it.[16] Secondly,
+    myopia, or short-sight, in which the eye is egg-shaped, and too long
+    from front to back; the retina in this case lies behind the focus, and
+    is therefore fitted to see distinctly only very near objects. This
+    condition is not commonly congenital, but comes on in youth, the
+    liability to it being well known to be transmissible from parent to
+    child. The change from the spherical to the ovoidal shape seems the
+    immediate {9} consequence of something like inflammation of the coats,
+    under which they yield, and there is ground for believing that it may
+    often originate in causes acting directly on the individual affected,
+    and may thenceforward become transmissible. When both parents are
+    myopic Mr. Bowman has observed the hereditary tendency in this
+    direction to be heightened, and some of the children to be myopic at an
+    earlier age or in a higher degree than their parents. Thirdly,
+    squinting is a familiar example of hereditary transmission: it is
+    frequently a result of such optical defects as have been above
+    mentioned; but the more primary and uncomplicated forms of it are also
+    sometimes in a marked degree transmitted in a family. Fourthly,
+    _Cataract_, or opacity of the crystalline lens, is commonly observed in
+    persons whose parents have been similarly affected, and often at an
+    earlier age in the children than in the parents. Occasionally more than
+    one child in a family is thus afflicted, one of whose parents or other
+    relation presents the senile form of the complaint. When cataract
+    affects several members of a family in the same generation, it is often
+    seen to commence at about the same age in each; _e.g._, in one family
+    several infants or young persons may suffer from it; in another,
+    several persons of middle age. Mr. Bowman also informs me that he has
+    occasionally seen, in several members of the same family, various
+    defects in either the right or left eye; and Mr. White Cooper has often
+    seen peculiarities of vision confined to one eye reappearing in the
+    same eye in the offspring.[17]
+
+    The following cases are taken from an able paper by Mr. W. Sedgwick,
+    and from Dr. Prosper Lucas.[18] Amaurosis, either congenital or coming
+    on late in life, and causing total blindness, is often inherited; it
+    has been observed in three successive generations. Congenital absence
+    of the iris has likewise been transmitted for three generations, a
+    cleft-iris for four generations, being limited in this latter case to
+    the males of the family. Opacity of the cornea and congenital smallness
+    of the eyes have been inherited. Portal records a curious case, in
+    which a father and two sons were rendered blind, whenever the head was
+    bent downwards, apparently owing to the crystalline lens, with its
+    capsule, slipping through an unusually large pupil into the anterior
+    chamber of the eye. Day-blindness, or imperfect vision under a bright
+    light, is inherited, as is night-blindness, or an incapacity to see
+    except under a strong light: a case has been recorded, by M. Cunier, of
+    this latter defect having affected eighty-five members of the same
+    family during six generations. The singular incapacity of
+    distinguishing colours, which has been called _Daltonism_, is
+    notoriously hereditary, and has been traced through five generations,
+    in which it was confined to the female sex.
+
+    With respect to the colour of the iris: deficiency of colouring matter
+    is well known to be hereditary in albinoes. The iris of one eye being
+    of a different colour from that of the other, and the iris being
+    spotted, are cases which have been inherited. Mr. Sedgwick gives, in
+    addition, on the {10} authority of Dr. Osborne,[19] the following
+    curious instance of strong inheritance: a family of sixteen sons and
+    five daughters all had eyes "resembling in miniature the markings on
+    the back of a tortoiseshell cat." The mother of this large family had
+    three sisters and a brother all similarly marked, and they derived this
+    peculiarity from their mother, who belonged to a family notorious for
+    transmitting it to their posterity.
+
+    Finally, Dr. Lucas emphatically remarks that there is not one single
+    faculty of the eye which is not subject to anomalies; and not one which
+    is not subjected to the principle of inheritance. Mr. Bowman agrees
+    with the general truth of this proposition; which of course does not
+    imply that all malformations are necessarily inherited; this would not
+    even follow if both parents were affected by an anomaly which in most
+    cases was transmissible.
+
+Even if no single fact had been known with respect to the inheritance of
+disease and malformations by man, the evidence would have been ample in the
+case of the horse. And this might have been expected, as horses breed much
+quicker than man, are matched with care, and are highly valued. I have
+consulted many works, and the unanimity of the belief by veterinaries of
+all nations in the transmission of various morbid tendencies is surprising.
+Authors, who have had wide experience, give in detail many singular cases,
+and assert that contracted feet, with the numerous contingent evils, of
+ring-bones, curbs, splints, spavin, founder and weakness of the front legs,
+roaring or broken and thick wind, melanosis, specific ophthalmia, and
+blindness (the great French veterinary Hazard going so far as to say that a
+blind race could soon be formed), crib-biting, jibbing, and ill-temper, are
+all plainly hereditary. Youatt sums up by saying "there is scarcely a
+malady to which the horse is subject which is not hereditary;" and M.
+Bernard adds that the doctrine "that there is scarcely a disease which does
+not run in the stock, is gaining new advocates every day."[20] So it {11}
+is in regard to cattle, with consumption, good and bad teeth, fine skin,
+&c. &c. But enough, and more than enough, has been said on disease. Andrew
+Knight, from his own experience, asserts that disease is hereditary with
+plants; and this assertion is endorsed by Lindley.[21]
+
+Seeing how hereditary evil qualities are, it is fortunate that good health,
+vigour, and longevity are equally inherited. It was formerly a well-known
+practice, when annuities were purchased to be received during the lifetime
+of a nominee, to search out a person belonging to a family of which many
+members had lived to extreme old age. As to the inheritance of vigour and
+endurance, the English race-horse offers an excellent instance. Eclipse
+begot 334, and King Herod 497 winners. A "cock-tail" is a horse not purely
+bred, but with only one-eighth or one-sixteenth impure blood in his veins,
+yet very few instances have ever occurred of such horses having won a great
+race. They are sometimes as fleet for short distances as thoroughbreds, but
+as Mr. Robson, the great trainer, asserts, they are deficient in wind, and
+cannot keep up the pace. Mr. Lawrence also remarks, "perhaps no instance
+has ever occurred of a three-part-bred horse saving his '_distance_' in
+running two miles with thoroughbred racers." It has been stated by Cecil,
+that when unknown horses, whose parents were not celebrated, have
+unexpectedly won great races, as in the case of Priam, they can always be
+proved to be descended on both sides, through many generations, from
+first-rate ancestors. On the Continent, Baron Cameronn challenges, in a
+German veterinary periodical, the opponents of the English race-horse, to
+name one good horse on the Continent which has not some English race-blood
+in his veins.[22]
+
+With respect to the transmission of the many slight, but {12} infinitely
+diversified characters, by which the domestic races of animals and plants
+are distinguished, nothing need be said; for the very existence of
+persistent races proclaims the power of inheritance.
+
+A few special cases, however, deserve some consideration. It might have
+been anticipated, that deviations from the law of symmetry would not have
+been inherited. But Anderson[23] states that a rabbit produced in a litter
+a young animal having only one ear; and from this animal a breed was formed
+which steadily produced one-eared rabbits. He also mentions a bitch, with a
+single leg deficient, and she produced several puppies with the same
+deficiency. From Hofacker's account[24] it appears that a one-horned stag
+was seen in 1781 in a forest in Germany, in 1788 two, and afterwards, from
+year to year, many were observed with only one horn on the right side of
+the head. A cow lost a horn by suppuration,[25] and she produced three
+calves which had on the same side of the head, instead of a horn, a small
+bony lump attached merely to the skin; but we here approach the doubtful
+subject of inherited mutilations. A man who is left-handed, and a shell in
+which the spire turns in the wrong direction, are departures from the
+normal though a symmetrical condition, and they are well known to be
+inherited.
+
+    _Polydactylism._--Supernumerary fingers and toes are eminently liable,
+    as various authors have insisted, to transmission, but they are noticed
+    here chiefly on account of their occasional regrowth after amputation.
+    Polydactylism graduates[26] by multifarious steps from a mere cutaneous
+    appendage, not including any bone, to a double hand. But an additional
+    digit, supported on a metacarpal bone, and furnished with all the
+    proper muscles, nerves, and vessels, is sometimes so perfect, that it
+    escapes detection, unless the fingers are actually counted.
+    Occasionally there are several supernumerary digits; but usually only
+    one, making the total number six. This one may represent either a thumb
+    or finger, being attached to the inner or outer margin of the hand.
+    Generally, through the law of correlation, both hands and feet are
+    similarly affected. I have tabulated the cases recorded in various
+    works or privately communicated {13} to me, of forty-six persons with
+    extra digits on one or both hands and feet; if in each case all four
+    extremities had been similarly affected, the table would have shown a
+    total of ninety-two hands and ninety-two feet each with six digits. As
+    it is, seventy-three hands and seventy-five feet were thus affected.
+    This proves, in contradiction to the result arrived at by Dr.
+    Struthers,[27] that the hands are not more frequently affected than the
+    feet.
+
+    The presence of more than five digits is a great anomaly, for this
+    number is not normally exceeded by any mammal, bird, or existing
+    reptile.[28] Nevertheless, supernumerary digits are strongly inherited;
+    they have been transmitted through five generations; and in some cases,
+    after disappearing for one, two, or even three generations, have
+    reappeared through reversion. These facts are rendered, as Professor
+    Huxley has observed, more remarkable from its being known in most cases
+    that the affected person had not married one similarly affected. In
+    such cases the child of the fifth generation would have only 1-32nd
+    part of the blood of his first sedigitated ancestor. Other cases are
+    rendered remarkable by the affection gathering force, as Dr. Struthers
+    has shown, in each generation, though in each the affected person had
+    married one not affected; moreover such additional digits are often
+    amputated soon after birth, and can seldom have been strengthened by
+    use. Dr. Struthers gives the following instance: in the first
+    generation an additional digit appeared on one hand; in the second, on
+    both hands; in the third, three brothers had both hands, and one of the
+    brothers a foot affected; and in the fourth generation all four limbs
+    were affected. Yet we must not over-estimate the force of inheritance.
+    Dr. Struthers asserts that cases of non-inheritance and of the first
+    appearance of additional digits in unaffected families are much more
+    frequent than cases of inheritance. Many other deviations of structure,
+    of a nature almost as anomalous as supernumerary digits, such as
+    deficient phalanges, thickened joints, crooked fingers, &c., are in
+    like manner strongly inherited, and are equally subject to intermission
+    with reversion, though in such cases there is no reason to suppose that
+    both parents had been similarly affected.[29]
+
+    {14}
+
+    Additional digits have been observed in negroes as well as in other
+    races of man, and in several of the lower animals. Six toes have been
+    described on the hind feet of the newt (_Salamandra cristata_), and, as
+    it is said, of the frog. It deserves notice from what follows, that the
+    six-toed newt, though adult, had preserved some of its larval
+    characters; for part of the hyoidal apparatus, which is properly
+    absorbed during the act of metamorphosis, was retained. In the dog, six
+    toes on the hinder feet have been transmitted through three
+    generations; and I have heard of a race of six-toed cats. In several
+    breeds of the fowl the hinder toe is double, and is generally
+    transmitted truly, as is well shown when Dorkings are crossed with
+    common four-toed breeds.[30] With animals which have properly less than
+    five digits, the number is sometimes increased to five, especially in
+    the front legs, though rarely carried beyond that number; but this is
+    due to the development of a digit already existing in a more or less
+    rudimentary state. Thus the dog has properly four toes behind, but in
+    the larger breeds a fifth toe is commonly, though not perfectly,
+    developed. Horses, which properly have one toe alone fully developed
+    with rudiments of the others, have been described with each foot
+    bearing two or three small separate hoofs: analogous facts have been
+    noticed with sheep, goats, and pigs.[31]
+
+    The most interesting point with respect to supernumerary digits is
+    their occasional regrowth after amputation. Mr. White[32] describes a
+    child, three years old, with a thumb double from the first joint. He
+    removed the lesser thumb, which was furnished with a nail; but to his
+    astonishment it grew again, and reproduced a nail. The child was then
+    taken to an eminent London surgeon, and the newly-grown thumb was
+    wholly removed by its socket-joint, but again it grew and reproduced a
+    nail. Dr. Struthers mentions a case of partial regrowth of an
+    additional thumb, amputated when the child was three months old; and
+    the late Dr. Falconer communicated to me an analogous case which had
+    fallen under his own observation. A gentleman, who first called my
+    attention to this subject, has given me the following facts which
+    occurred in his own family. He himself, two brothers, and a sister were
+    born with an extra digit to each extremity. His parents were not
+    affected, and there was no tradition in the family, or in the village
+    in which the family had long resided, of any member having been thus
+    affected. Whilst a child, both additional toes, which were attached by
+    bones, were rudely cut off; but the stump of one grew again, and a
+    second operation was performed in his thirty-third year.
+
+    {15}
+
+    He has had fourteen children, of whom three have inherited additional
+    digits; and one of them, when about six weeks old, was operated on by
+    an eminent surgeon. The additional finger, which was attached by bone
+    to the outer side of the hand, was removed at the joint; the wound
+    healed, but immediately the digit began growing; and in about three
+    months' time the stump was removed for the second time by the root. But
+    it has since grown again, and is now fully a third of an inch in
+    length, including a bone; so that it will for the third time have to be
+    operated on.
+
+    Now the normal digits in adult man and other mammals, in birds, and, as
+    I believe, in true reptiles, have no power of regrowth. The nearest
+    approach to this power is exhibited by the occasional reappearance in
+    man of imperfect nails on the stumps of his fingers after
+    amputation.[33] But man in his embryonic condition has a considerable
+    power of reproduction, for Sir J. Simpson[34] has several times
+    observed arms which had been cut off in the womb by bands of false
+    membrane, and which had grown again to a certain extent. In one
+    instance, the extremity was "divided into three minute nodules, on two
+    of which small points of nails could be detected;" so that these
+    nodules clearly represented fingers in process of regrowth. When,
+    however, we descend to the lower vertebrate classes, which are
+    generally looked at as representing the higher classes in their
+    embryonic condition, we find ample powers of regrowth. Spallanzani[35]
+    cut off the legs and tail of a salamander six times, and Bonnet eight
+    times, successively, and they were reproduced. An additional digit
+    beyond the proper number was occasionally formed after Bonnet had cut
+    off or had divided longitudinally the hand or foot, and in one instance
+    three additional digits were thus formed.[36] These latter cases appear
+    at first sight quite distinct from the congenital production of
+    additional digits in the higher animals; but theoretically, as we shall
+    see in a future chapter, they probably present no real difference. The
+    larvae or tadpoles of the tailless Batrachians, but not the adults,[37]
+    are capable of reproducing lost members.[38] Lastly, as I have been
+    informed by Mr. J. J. Briggs and Mr. F. Buckland, when portions of the
+    pectoral and tail fins of various {16} fresh-water fish are cut off,
+    they are perfectly reproduced in about six weeks' time.
+
+From these several facts we may infer that supernumerary digits in man
+retain to a certain extent an embryonic condition, and that they resemble
+in this respect the normal digits and limbs in the lower vertebrate
+classes. They also resemble the digits of some of the lower animals in the
+number exceeding five; for no mammal, bird, existing reptile, or amphibian
+(unless the tubercle on the hind feet of the toad and other tailless
+Batrachians be viewed as a digit) has more than five; whilst fishes
+sometimes have in their pectoral fins as many as twenty metacarpal and
+phalangeal bones, which, together with the bony filaments, apparently
+represent our digits with their nails. So, again, in certain extinct
+reptiles, namely, the Ichthyopterygia, "the digits may be seven, eight, or
+nine in number, a significant mark," says Professor Owen, "of piscine
+affinity."[39]
+
+We encounter much difficulty in attempting to reduce these various facts to
+any rule or law. The inconstant number of the additional digits--their
+irregular attachment to either the inner or outer margin of the hand--the
+gradation which can be traced from a mere loose rudiment of a single digit
+to a completely double hand--the occasional appearance of additional digits
+in the salamander after a limb has been amputated--these various facts
+appear to indicate mere fluctuating monstrosity; and this perhaps is all
+that can be safely said. Nevertheless, as supernumerary digits in the
+higher animals, from their power of regrowth and from the number thus
+acquired exceeding five, partake of the nature of the digits in the lower
+vertebrate animals;--as they occur by no means rarely, and are transmitted
+with remarkable strength, though perhaps not more strongly than some other
+anomalies;--and as with animals which have fewer than five digits, when an
+additional one appears it is generally due to the development of a visible
+rudiment;--we are led in all cases to suspect, that, although no actual
+rudiment can be detected, yet that a latent tendency to the formation of an
+additional digit exists in all mammals, including man. On this view, as we
+shall more plainly see in the {17} next chapter when discussing latent
+tendencies, we should have to look at the whole case as one of reversion to
+an enormously remote, lowly-organised, and multidigitate progenitor.
+
+       *       *       *       *       *
+
+I may here allude to a class of facts closely allied to, but somewhat
+different from, ordinary cases of inheritance. Sir H. Holland[40] states
+that brothers and sisters of the same family are frequently affected, often
+at about the same age, by the same peculiar disease, not known to have
+previously occurred in the family. He specifies the occurrence of diabetes
+in three brothers under ten years old; he also remarks that children of the
+same family often exhibit in common infantile diseases the same peculiar
+symptoms. My father mentioned to me the case of four brothers who died
+between the ages of sixty and seventy, in the same highly peculiar comatose
+state. An instance has been already given of supernumerary digits appearing
+in four children out of six in a previously unaffected family. Dr. Devay
+states[41] that two brothers married two sisters, their first-cousins, none
+of the four nor any relation being an albino; but the seven children
+produced from this double marriage were all perfect albinoes. Some of these
+cases, as Mr. Sedgwick[42] has shown, are probably the result of reversion
+to a remote ancestor, of whom no record had been preserved; and all these
+cases are so far directly connected with inheritance that no doubt the
+children inherited a similar constitution from their parents, and, from
+being exposed to nearly similar conditions of life, it is not surprising
+that they should be affected in the same manner and at the same period of
+life.
+
+       *       *       *       *       *
+
+Most of the facts hitherto given have served to illustrate the force of
+inheritance, but we must now consider cases, grouped as well as the subject
+allows into classes, showing how feeble, capricious, or deficient the power
+of inheritance sometimes is. When a new peculiarity first appears, we can
+never predict whether it will be inherited. If both parents from their
+birth present {18} the same peculiarity, the probability is strong that it
+will be transmitted to at least some of their offspring. We have seen that
+variegation is transmitted much more feebly by seed from a branch which had
+become variegated through bud-variation, than from plants which were
+variegated as seedlings. With most plants the power of transmission
+notoriously depends on some innate capacity in the individual: thus
+Vilmorin[43] raised from a peculiarly coloured balsam some seedlings, which
+all resembled their parent; but of these seedlings some failed to transmit
+the new character, whilst others transmitted it to all their descendants
+during several successive generations. So again with a variety of the rose,
+two plants alone out of six were found by Vilmorin to be capable of
+transmitting the desired character.
+
+    The weeping or pendulous growth of trees is strongly inherited in some
+    cases, and, without any assignable reason, feebly in other cases. I
+    have selected this character as an instance of capricious inheritance,
+    because it is certainly not proper to the parent-species, and because,
+    both sexes being borne on the same tree, both tend to transmit the same
+    character. Even supposing that there may have been in some instances
+    crossing with adjoining trees of the same species, it is not probable
+    that all the seedlings would have been thus affected. At Moccas Court
+    there is a famous weeping oak; many of its branches "are 30 feet long,
+    and no thicker in any part of this length than a common rope:" this
+    tree transmits its weeping character, in a greater or less degree, to
+    all its seedlings; some of the young oaks being so flexible that they
+    have to be supported by props; others not showing the weeping tendency
+    till about twenty years old.[44] Mr. Rivers fertilized, as he informs
+    me, the flowers of a new Belgian weeping thorn (_Crataegus oxyacantha_)
+    with pollen from a crimson not-weeping variety, and three young trees,
+    "now six or seven years old, show a decided tendency to be pendulous,
+    but as yet are not so much so as the mother-plant." According to Mr.
+    MacNab,[45] seedlings from a magnificent weeping birch (_Betula alba_),
+    in the Botanic Garden at Edinburgh, grew for the first ten or fifteen
+    years upright, but then all became weepers like their parent. A peach
+    with pendulous branches, like those of the weeping willow, has been
+    found capable of propagation by seed.[46] Lastly, a weeping and almost
+    prostrate yew (_Taxus baccata_) was found in a hedge in Shropshire; it
+    was a male, but one branch bore female flowers, and produced berries;
+    these, {19} being sown, produced seventeen trees, all of which had
+    exactly the same peculiar habit with the parent-tree.[47]
+
+    These facts, it might have been thought, would have been sufficient to
+    render it probable that a pendulous habit would in all cases be
+    strictly inherited. But let us look to the other side. Mr. MacNab[48]
+    sowed seeds of the weeping beech (_Fagus sylvanica_), but succeeded in
+    raising only common beeches. Mr. Rivers, at my request, raised a number
+    of seedlings from three distinct varieties of weeping elm; and at least
+    one of the parent-trees was so situated that it could not have been
+    crossed by any other elm; but none of the young trees, now about a foot
+    or two in height, show the least signs of weeping. Mr. Rivers formerly
+    sowed above twenty thousand seeds of the weeping ash (_Fraxinus
+    excelsior_), and not a single seedling was in the least degree
+    pendulous: in Germany, M. Borchmeyer raised a thousand seedlings, with
+    the same result. Nevertheless, Mr. Anderson, of the Chelsea Botanic
+    Garden, by sowing seed from a weeping ash, which was found before the
+    year 1780, in Cambridgeshire, raised several pendulous trees.[49]
+    Professor Henslow also informs me that some seedlings from a female
+    weeping ash in the Botanic Garden at Cambridge were at first a little
+    pendulous, but afterwards became quite upright: it is probable that
+    this latter tree, which transmits to a certain extent its pendulous
+    habit, was derived by a bud from the same original Cambridgeshire
+    stock; whilst other weeping ashes may have had a distinct origin. But
+    the crowning case, communicated to me by Mr. Rivers, which shows how
+    capricious is the inheritance of a pendulous habit, is that a variety
+    of another species of ash (_F. lentiscifolia_) which was formerly
+    pendulous, "now about twenty years old has long lost this habit, every
+    shoot being remarkably erect; but seedlings formerly raised from it
+    were perfectly prostrate, the stems not rising more than two inches
+    above the ground." Thus the weeping variety of the common ash, which
+    has been extensively propagated by buds during a long period, did not,
+    with Mr. Rivers, transmit its character to one seedling out of above
+    twenty thousand; whereas the weeping variety of a second species of
+    ash, which could not, whilst grown in the same garden, retain its own
+    weeping character, transmitted to its seedlings the pendulous habit in
+    excess!
+
+    Many analogous facts could be given, showing how apparently capricious
+    is the principle of inheritance. All the seedlings from a variety of
+    the Barberry (_B. vulgaris_) with red leaves inherited the same
+    character; only about one-third of the seedlings of the copper Beech
+    (_Fagus sylvatica_) had purple leaves. Not one out of a hundred
+    seedlings of a variety of the _Cerasus padus_, with yellow fruit, bore
+    yellow fruit: one-twelfth of the seedlings of the variety of _Cornus
+    mascula_, with yellow fruit, came true:[50] and lastly, all the trees
+    raised by my father from a yellow-berried holly (_Ilex aquifolium_),
+    {20} found wild, produced yellow berries. Vilmorin[51] observed in a
+    bed of _Saponaria calabrica_ an extremely dwarf variety, and raised
+    from it a large number of seedlings; some of these partially resembled
+    their parent, and he selected their seed; but the grandchildren were
+    not in the least dwarfed: on the other hand, he observed a stunted and
+    bushy variety of _Tagetes signata_ growing in the midst of the common
+    varieties by which it was probably crossed; for most of the seedlings
+    raised from this plant were intermediate in character, only two
+    perfectly resembling their parent; but seed saved from these two plants
+    reproduced the new variety so truly, that hardly any selection has
+    since been necessary.
+
+    Flowers transmit their colour truly, or most capriciously. Many annuals
+    come true: thus I purchased German seeds of thirty-four named
+    sub-varieties of one _race_ of ten-week stocks (_Matthiola annua_), and
+    raised a hundred and forty plants, all of which, with the exception of
+    a single plant, came true. In saying this, however, it must be
+    understood that I could distinguish only twenty kinds out of the
+    thirty-four named sub-varieties; nor did the colour of the flower
+    always correspond with the name affixed to the packet; but I say that
+    they came true, because in each of the thirty-six short rows every
+    plant was absolutely alike, with the one single exception. Again, I
+    procured packets of German seed of twenty-five named varieties of
+    common and quilled asters, and raised a hundred and twenty-four plants;
+    of these, all except ten were true in the above limited sense; and I
+    considered even a wrong shade of colour as false.
+
+    It is a singular circumstance that white varieties generally transmit
+    their colour much more truly than any other variety. This fact probably
+    stands in close relation with one observed by Verlot,[52] namely, that
+    flowers which are normally white rarely vary into any other colour. I
+    have found that the white varieties of _Delphinium consolida_ and of
+    the Stock are the truest. It is, indeed, sufficient to look through a
+    nurseryman's seed-list, to see the large number of white varieties
+    which can be propagated by seed. The several coloured varieties of the
+    sweet-pea (_Lathyrus odoratus_) are very true; but I hear from Mr.
+    Masters, of Canterbury, who has particularly attended to this plant,
+    that the white variety is the truest. The hyacinth, when propagated by
+    seed, is extremely inconstant in colour, but "white hyacinths almost
+    always give by seed white-flowered plants;"[53] and Mr. Masters informs
+    me that the yellow varieties also reproduce their colour, but of
+    different shades. On the other hand, pink and blue varieties, the
+    latter being the natural colour, are not nearly so true: hence, as Mr.
+    Masters has remarked to me, "we see that a garden variety may acquire a
+    more permanent habit than a natural species;" but it should have been
+    added, that this occurs under cultivation, and therefore under changed
+    conditions.
+
+    With many flowers, especially perennials, nothing can be more
+    fluctuating than the colour of the seedlings, as is notoriously the
+    case with verbenas, carnations, dahlias, cinerarias, and others.[54] I
+    sowed seed of twelve {21} named varieties of Snapdragon (_Antirrhinum
+    majus_), and utter confusion was the result. In most cases the
+    extremely fluctuating colour of seedling plants is probably in chief
+    part due to crosses between differently-coloured varieties during
+    previous generations. It is almost certain that this is the case with
+    the polyanthus and coloured primrose (_Primula veris_ and _vulgaris_),
+    from their reciprocally dimorphic structure;[55] and these are plants
+    which florists speak of as never come true by seed: but if care be
+    taken to prevent crossing, neither species is by any means very
+    inconstant in colour; thus I raised twenty-three plants from a purple
+    primrose, fertilised by Mr. J. Scott with its own pollen, and eighteen
+    came up purple of different shades, and only five reverted to the
+    ordinary yellow colour: again, I raised twenty plants from a bright-red
+    cowslip, similarly treated by Mr. Scott, and every one perfectly
+    resembled its parent in colour, as likewise did, with the exception of
+    a single plant, 73 grandchildren. Even with the most variable flowers,
+    it is probable that each delicate shade of colour might be permanently
+    fixed so as to be transmitted by seed, by cultivation in the same soil,
+    by long-continued selection, and especially by the prevention of
+    crosses. I infer this from certain annual larkspurs (_Delphinium
+    consolida_ and _ajacis_), of which common seedlings present a greater
+    diversity of colour than any other plant known to me; yet on procuring
+    seed of five named German varieties of _D. consolida_, only nine plants
+    out of ninety-four were false; and the seedlings of six varieties of
+    _D. ajacis_ were true in the same manner and degree as with the stocks
+    above described. A distinguished botanist maintains that the annual
+    species of Delphinium are always self-fertilised; therefore I may
+    mention that thirty-two flowers on a branch of _D. consolida_, enclosed
+    in a net, yielded twenty-seven capsules, with an average of 17.2 seed
+    in each; whilst five flowers, under the same net, which were
+    artificially fertilised, in the same manner as must be effected by bees
+    during their incessant visits, yielded five capsules with an average of
+    35.2 fine seed; and this shows that the agency of insects is necessary
+    for the full fertility of this plant. Analogous facts could be given
+    with respect to the crossing of many other flowers, such as carnations,
+    &c., of which the varieties fluctuate much in colour.
+
+    As with flowers, so with our domesticated animals, no character is more
+    variable than colour, and probably in no animal more so than with the
+    horse. Yet with a little care in breeding, it appears that races of any
+    colour might soon be formed. Hofacker gives the result of matching two
+    hundred and sixteen mares of four different colours with like-coloured
+    stallions, without regard to the colour of their ancestors; and of the
+    two hundred and sixteen colts born, eleven alone failed to inherit the
+    colour of their parents: Autenrieth and Ammon assert that, after two
+    generations, colts of a uniform colour are produced with certainty.[56]
+
+In a few rare cases peculiarities fail to be inherited, apparently from the
+force of inheritance being too strong. I have been assured by breeders of
+the canary-bird that to get a good {22} jonquil-coloured bird it does not
+answer to pair two jonquils, as the colour then comes out too strong, or is
+even brown. So again, if two crested canaries are paired, the young birds
+rarely inherit this character:[57] for in crested birds a narrow space of
+bare skin is left on the back of the head, where the feathers are up-turned
+to form the crest, and, when both parents are thus characterised, the
+bareness becomes excessive, and the crest itself fails to be developed. Mr.
+Hewitt, speaking of Laced Sebright Bantams, says[58] that, "why this should
+be so, I know not, but I am confident that those that are best laced
+frequently produce offspring very far from perfect in their markings,
+whilst those exhibited by myself, which have so often proved successful,
+were bred from the union of heavily-laced birds with those that were
+scarcely sufficiently laced."
+
+It is a singular fact that, although several deaf-mutes often occur in the
+same family, and though their cousins and other relations are often in the
+same condition, yet their parents are very rarely deaf-mutes. To give a
+single instance: not one scholar out of 148, who were at the same time in
+the London Institution, was the child of parents similarly afflicted. So
+again, when a male or a female deaf-mute marries a sound person, their
+children are most rarely affected: in Ireland out of 203 children thus
+produced one alone was mute. Even when both parents have been deaf-mutes,
+as in the case of forty-one marriages in the United States and of six in
+Ireland, only two deaf and dumb children were produced. Mr. Sedgwick,[59]
+in commenting on this remarkable and fortunate failure in the power of
+transmission in the direct line, remarks that it may possibly be owing to
+"excess having reversed the action of some natural law in development." But
+it is safer in the present state of our knowledge to look at the whole case
+as simply unintelligible.
+
+       *       *       *       *       *
+
+With respect to the inheritance of structures mutilated by injuries or
+altered by disease it is difficult to come to any {23} definite conclusion.
+In some cases mutilations have been practised for a vast number of
+generations without any inherited result. Godron has remarked[60] that
+different races of man have from time immemorial knocked out their upper
+incisors, cut off joints of their fingers, made holes of immense size
+through the lobes of their ears or through their nostrils, made deep gashes
+in various parts of their bodies, and there is no reason whatever to
+suppose that these mutilations have ever been inherited. Adhesions due to
+inflammation and pits from the small-pox (and formerly many consecutive
+generations must have been thus pitted) are not inherited. With respect to
+Jews, I have been assured by three medical men of the Jewish faith that
+circumcision, which has been practised for so many ages, has produced no
+inherited effect; Blumenbach, on the other hand, asserts[61] that in
+Germany Jews are often born in a condition rendering circumcision
+difficult, so that a name is here applied to them signifying "born
+circumcised." The oak and other trees must have borne galls from primeval
+times, yet they do not produce inherited excrescences; many other such
+facts could be adduced.
+
+On the other hand, various cases have been recorded of cats, dogs, and
+horses, which have had their tails, legs, &c., amputated or injured,
+producing offspring with the same parts ill-formed; but as it is not at all
+rare for similar malformations to appear spontaneously, all such cases may
+be due to mere coincidence. Nevertheless, Dr. Prosper Lucas has given, on
+good authorities, such a long list of inherited injuries, that it is
+difficult not to believe in them. Thus, a cow that had lost a horn from an
+accident with consequent suppuration, produced three calves which were
+hornless on the same side of the head. With the horse, there seems hardly a
+doubt that bony exostoses on the legs, caused by too much travelling on
+hard roads, are inherited. Blumenbach records the case of a man who had his
+little finger on the right hand almost cut off, and which in consequence
+grew crooked, and his sons had the same finger on the same hand similarly
+crooked. A soldier, fifteen years before his marriage, lost his left eye
+from purulent ophthalmia, and his {24} two sons were microphthalmic on the
+same side.[62] In all such cases, if truthfully reported, in which the
+parent has had an organ injured on one side, and more than one child has
+been born with the same organ affected on the same side, the chances
+against mere coincidence are enormous. But perhaps the most remarkable and
+trustworthy fact is that given by Dr. Brown-Sequard,[63] namely, that many
+young guinea-pigs inherited an epileptic tendency from parents which had
+been subjected to a particular operation, inducing in the course of a few
+weeks a convulsive disease like epilepsy: and it should be especially noted
+that this eminent physiologist bred a large number of guinea-pigs from
+animals which had not been operated on, and not one of these manifested the
+epileptic tendency. On the whole, we can hardly avoid admitting, that
+injuries and mutilations, especially when followed by disease, or perhaps
+exclusively when thus followed, are occasionally inherited.
+
+Although many congenital monstrosities are inherited, of which examples
+have already been given, and to which may be added the lately recorded case
+of the transmission during a century of hare-lip with a cleft-palate in the
+writer's own family,[64] yet other malformations are rarely or never
+inherited. Of these later cases, many are probably due to injuries in the
+womb or egg, and would come under the head of non-inherited injuries or
+mutilations. With plants, a long catalogue of inherited monstrosities of
+the most serious and diversified nature could easily be given; and with
+plants, there is no reason to suppose that monstrosities are caused by
+direct injuries to the seed or embryo.
+
+_Causes of Non-inheritance._
+
+A large number of cases of non-inheritance are intelligible on the
+principle, that a strong tendency to inheritance does exist, but {25} that
+it is overborne by hostile or unfavourable conditions of life. No one would
+expect that our improved pigs, if forced during several generations to
+travel about and root in the ground for their own subsistence, would
+transmit, as truly as they now do, their tendency to fatten, and their
+short muzzles and legs. Dray-horses assuredly would not long transmit their
+great size and massive limbs, if compelled to live on a cold, damp
+mountainous region; we have indeed evidence of such deterioration in the
+horses which have run wild on the Falkland Islands. European dogs in India
+often fail to transmit their true character. Our sheep in tropical
+countries lose their wool in a few generations. There seems also to be a
+close relation between certain peculiar pastures and the inheritance of an
+enlarged tail in fat-tailed sheep, which form one of the most ancient
+breeds in the world. With plants, we have seen that the American varieties
+of maize lose their proper character in the course of two or three
+generations, when cultivated in Europe. Our cabbages, which here come so
+true by seed, cannot form heads in hot countries. Under changed
+circumstances, periodical habits of life soon fail to be transmitted, as
+the period of maturity in summer and winter wheat, barley, and vetches. So
+it is with animals; for instance, a person whose statement I can trust,
+procured eggs of Aylesbury ducks from that town, where they are kept in
+houses and are reared as early as possible for the London market; the ducks
+bred from these eggs in a distant part of England, hatched their first
+brood on January 24th, whilst common ducks, kept in the same yard and
+treated in the same manner, did not hatch till the end of March; and this
+shows that the period of hatching was inherited. But the grandchildren of
+these Aylesbury ducks completely lost their early habit of incubation, and
+hatched their eggs at the same time with the common ducks of the same
+place.
+
+Many cases of non-inheritance apparently result from the conditions of life
+continually inducing fresh variability. We have seen that when the seeds of
+pears, plums, apples, &c., are sown, the seedlings generally inherit some
+degree of family likeness from the parent-variety. Mingled with these
+seedlings, a few, and sometimes many, worthless, wild-looking plants
+commonly appear; and their appearance may be attributed to the principle of
+reversion. But scarcely a single seedling will be found {26} perfectly to
+resemble the parent-form; and this, I believe, may be accounted for by
+constantly recurring variability induced by the conditions of life. I
+believe in this, because it has been observed that certain fruit-trees
+truly propagate their kind whilst growing on their own roots, but when
+grafted on other stocks, and by this process their natural state is
+manifestly affected, they produce seedlings which vary greatly, departing
+from the parental type in many characters.[65] Metzger, as stated in the
+ninth chapter, found that certain kinds of wheat brought from Spain and
+cultivated in Germany, failed during many years to reproduce themselves
+truly; but that at last, when accustomed to their new conditions, they
+ceased to be variable,--that is, they became amenable to the power of
+inheritance. Nearly all the plants which cannot be propagated with any
+approach to certainty by seed, are kinds which have long been propagated by
+buds, cuttings, offsets, tubers, &c., and have in consequence been
+frequently exposed during their individual lives to widely diversified
+conditions of life. Plants thus propagated become so variable, that they
+are subject, as we have seen in the last chapter, even to bud-variation.
+Our domesticated animals, on the other hand, are not exposed during their
+individual lives to such extremely diversified conditions, and are not
+liable to such extreme variability; therefore they do not lose the power of
+transmitting most of their characteristic features. In the foregoing
+remarks on non-inheritance, crossed breeds are of course excluded, as their
+diversity mainly depends on the unequal development of characters derived
+from either parent, modified by the principles of reversion and prepotency.
+
+_Conclusion._
+
+It has, I think, been shown in the early part of this chapter how strongly
+new characters of the most diversified nature, whether normal or abnormal,
+injurious or beneficial, whether affecting organs of the highest or most
+trifling importance, are inherited. Contrary to the common opinion, it is
+often sufficient for the inheritance of some peculiar character, that one
+parent alone should possess it, as in most cases in which the rarer {27}
+anomalies have been transmitted. But the power of transmission is extremely
+variable: in a number of individuals descended from the same parents, and
+treated in the same manner, some display this power in a perfect manner,
+and in some it is quite deficient; and for this difference no reason can be
+assigned. In some cases the effects of injuries or mutilations apparently
+are inherited; and we shall see in a future chapter that the effects of the
+long-continued use and disuse of parts are certainly inherited. Even those
+characters which are considered the most fluctuating, such as colour, are
+with rare exceptions transmitted much more forcibly than is generally
+supposed. The wonder, indeed, in all cases is not that any character should
+be transmitted, but that the power of inheritance should ever fail. The
+checks to inheritance, as far as we know them, are, firstly, circumstances
+hostile to the particular character in question; secondly, conditions of
+life incessantly inducing fresh variability; and lastly, the crossing of
+distinct varieties during some previous generation, together with reversion
+or atavism--that is, the tendency in the child to resemble its
+grand-parents or more remote ancestors instead of its immediate parents.
+This latter subject will be fully discussed in the following chapter.
+
+       *       *       *       *       *
+
+
+{28}
+
+CHAPTER XIII.
+
+INHERITANCE _continued_--REVERSION OR ATAVISM.
+
+    DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN
+    PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED
+    PLANTS--REVERSION IN FERAL ANIMALS AND PLANTS--REVERSION IN CROSSED
+    VARIETIES AND SPECIES--REVERSION THROUGH BUD-PROPAGATION, AND BY
+    SEGMENTS IN THE SAME FLOWER OR FRUIT--IN DIFFERENT PARTS OF THE BODY IN
+    THE SAME ANIMAL--THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION,
+    VARIOUS CASES OF, WITH INSTINCTS--OTHER PROXIMATE CAUSES OF
+    REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL CHARACTERS--UNEQUAL
+    DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE WITH ADVANCING AGE
+    OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALL ITS LATENT
+    CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS DUE IN
+    SOME CASES TO REVERSION.
+
+The great principle of inheritance to be discussed in this chapter has been
+recognised by agriculturists and authors of various nations, as shown by
+the scientific term _Atavism_, derived from atavus, an ancestor; by the
+English terms of _Reversion_, or _Throwing back_; by the French
+_Pas-en-arriere_; and by the German _Rueck-schlag_, or _Rueck-schritt_.
+When the child resembles either grandparent more closely than its immediate
+parents, our attention is not much arrested, though in truth the fact is
+highly remarkable; but when the child resembles some remote ancestor, or
+some distant member in a collateral line,--and we must attribute the latter
+case to the descent of all the members from a common progenitor,--we feel a
+just degree of astonishment. When one parent alone displays some
+newly-acquired and generally inheritable character, and the offspring do
+not inherit it, the cause may lie in the other parent having the power of
+prepotent transmission. But when both parents are similarly characterised,
+and the child does not, whatever the cause may be, inherit the character in
+question, but resembles its grandparents, we have one of the simplest cases
+of reversion. We continually see another and even more simple case of
+atavism, though not generally included under this head, namely, when {29}
+the son more closely resembles his maternal than his paternal grandsire in
+some male attribute, as in any peculiarity in the beard of man, the horns
+of the bull, the hackles or comb of the cock, or, as in certain diseases
+necessarily confined to the male sex; for the mother cannot possess or
+exhibit such male attributes, yet the child has inherited them, through her
+blood, from his maternal grandsire.
+
+The cases of reversion may be divided into two main classes, which,
+however, in some instances, blend into each other; namely, first, those
+occurring in a variety or race which has not been crossed, but has lost by
+variation some character that it formerly possessed, and which afterwards
+reappears. The second class includes all cases in which a distinguishable
+individual, sub-variety, race, or species, has at some former period been
+crossed with a distinct form, and a character derived from this cross,
+after having disappeared during one or several generations, suddenly
+reappears. A third class, differing only in the manner of reproduction,
+might be formed to include all cases of reversion effected by means of
+buds, and therefore independent of true or seminal generation. Perhaps even
+a fourth class might be instituted, to include reversions by segments in
+the same individual flower or fruit, and in different parts of the body in
+the same individual animal as it grows old. But the two first main classes
+will be sufficient for our purpose.
+
+       *       *       *       *       *
+
+_Reversion to lost Characters by pure or uncrossed forms._--Striking
+instances of this first class of cases were given in the sixth chapter,
+namely, of the occasional reappearance, in variously-coloured pure breeds
+of the pigeon, of blue birds with all the marks which characterise the wild
+_Columba livia_. Similar cases were given in the case of the fowl. With the
+common ass, as we now know that the legs of the wild progenitor are
+striped, we may feel assured that the occasional appearance of such stripes
+in the domestic animal is a case of simple reversion. But I shall be
+compelled to refer again to these cases, and therefore will here pass them
+over.
+
+The aboriginal species from which our domesticated cattle and sheep are
+descended, no doubt possessed horns; but several hornless breeds are now
+well established. Yet in these--for instance, {30} in Southdown sheep--"it
+is not unusual to find among the male lambs some with small horns." The
+horns, which thus occasionally reappear in other polled breeds, either
+"grow to the full size, or are curiously attached to the skin alone and
+hang loosely down, or drop off."[66] The Galloways and Suffolk cattle have
+been hornless for the last 100 or 150 years, but a horned calf, with the
+horn often loosely attached, is occasionally born.[67]
+
+There is reason to believe that sheep in their early domesticated condition
+were "brown or dingy black;" but even in the time of David certain flocks
+were spoken of as white as snow. During the classical period the sheep of
+Spain are described by several ancient authors as being black, red, or
+tawny.[68] At the present day, notwithstanding the great care which is
+taken to prevent it, particoloured lambs and some entirely black are
+occasionally dropped by our most highly improved and valued breeds, such as
+the Southdowns. Since the time of the famous Bakewell, during the last
+century, the Leicester sheep have been bred with the most scrupulous care;
+yet occasionally grey-faced, or black-spotted, or wholly black lambs
+appear.[69] This occurs still more frequently with the less improved
+breeds, such as the Norfolks.[70] As bearing on this tendency in sheep to
+revert to dark colours, I may state (though in doing so I trench on the
+reversion of crossed breeds, and likewise on the subject of prepotency)
+that the Rev. W. D. Fox was informed that seven white Southdown ewes were
+put to a so-called Spanish ram, which had two small black spots on his
+sides, and they produced thirteen lambs, all perfectly black. Mr. Fox
+believes that this ram belonged to a breed which he has himself kept, and
+which is always spotted with black and white; and he finds that Leicester
+sheep crossed by rams of this breed always produce black lambs: he has gone
+on recrossing these crossed sheep with pure white Leicesters during three
+successive {31} generations, but always with the same result. Mr. Fox was
+also told by the friend from whom the spotted breed was procured, that he
+likewise had gone on for six or seven generations crossing with white
+sheep, but still black lambs were invariably produced.
+
+Similar facts could be given with respect to tailless breeds of various
+animals. For instance, Mr. Hewitt[71] states that chickens bred from some
+Rumpless fowls, which were reckoned so good that they won a prize at an
+exhibition, "in a considerable number of instances were furnished with
+fully developed tail-feathers." On inquiry, the original breeder of these
+fowls stated that, from the time when he had first kept them, they had
+often produced fowls furnished with tails; but that these latter would
+again reproduce rumpless chickens.
+
+Analogous cases of reversion occur in the vegetable kingdom; thus "from
+seeds gathered from the finest cultivated varieties of Heartsease (_Viola
+tricolor_), plants perfectly wild both in their foliage and their flowers
+are frequently produced;"[72] but the reversion in this instance is not to
+a very ancient period, for the best existing varieties of the heartsease
+are of comparatively modern origin. With most of our cultivated vegetables
+there is some tendency to reversion to what is known to be, or may be
+presumed to be, their aboriginal state; and this would be more evident if
+gardeners did not generally look over their beds of seedlings, and pull up
+the false plants or "rogues" as they are called. It has already been
+remarked, that some few seedling apples and pears generally resemble, but
+apparently are not identical with, the wild trees from which they are
+descended. In our turnip[73] and carrot-beds a few plants often
+"break"--that is, flower too soon; and their roots are generally found to
+be hard and stringy, as in the parent-species. By the aid of a little
+selection, carried on during a few generations, most of our cultivated
+plants could probably be brought back, without any great change in their
+conditions of life, to a wild or nearly wild condition: Mr. Buckman has
+effected this with the parsnip;[74] {32} and Mr. Hewett C. Watson, as he
+informs me, selected, during three generations, "the most diverging plants
+of Scotch kail, perhaps one of the least modified varieties of the cabbage;
+and in the third generation some of the plants came very close to the forms
+now established in England about old castle-walls, and called indigenous."
+
+       *       *       *       *       *
+
+_Reversion in Animals and Plants which have run wild._--In the cases
+hitherto considered, the reverting animals and plants have not been exposed
+to any great or abrupt change in their conditions of life which could have
+induced this tendency; but it is very different with animals and plants
+which have become feral or run wild. It has been repeatedly asserted in the
+most positive manner by various authors, that feral animals and plants
+invariably return to their primitive specific type. It is curious on what
+little evidence this belief rests. Many of our domesticated animals could
+not subsist in a wild state; thus, the more highly improved breeds of the
+pigeon will not "field" or search for their own food. Sheep have never
+become feral, and would be destroyed by almost every beast of prey. In
+several cases we do not know the aboriginal parent-species, and cannot
+possibly tell whether or not there has been any close degree of reversion.
+It is not known in any instance what variety was first turned out; several
+varieties have probably in some cases run wild, and their crossing alone
+would tend to obliterate their proper character. Our domesticated animals
+and plants, when they run wild, must always be exposed to new conditions of
+life, for, as Mr. Wallace[75] has well remarked, they have to obtain their
+own food, and are exposed to competition with the native productions. Under
+these circumstances, if our domesticated animals did not undergo change of
+some kind, the result would be quite opposed to the conclusions arrived at
+in this work. Nevertheless, I do not doubt that the simple fact of animals
+and plants becoming feral, does cause some tendency to reversion to the
+primitive state; though this tendency has been much exaggerated by some
+authors.
+
+{33}
+
+    I will briefly run through the recorded cases. With neither horses nor
+    cattle is the primitive stock known; and it has been shown in former
+    chapters that they have assumed different colours in different
+    countries. Thus the horses which have run wild in South America are
+    generally brownish-bay, and in the East dun-coloured; their heads have
+    become larger and coarser, and this may be due to reversion. No careful
+    description has been given of the feral goat. Dogs which have run wild
+    in various countries have hardly anywhere assumed a uniform character;
+    but they are probably descended from several domestic races, and
+    aboriginally from several distinct species. Feral cats, both in Europe
+    and La Plata, are regularly striped; in some cases they have grown to
+    an unusually large size, but do not differ from the domestic animal in
+    any other character. When variously-coloured tame rabbits are turned
+    out in Europe, they generally reacquire the colouring of the wild
+    animal; there can be no doubt that this does really occur, but we
+    should remember that oddly-coloured and conspicuous animals would
+    suffer much from beasts of prey and from being easily shot; this at
+    least was the opinion of a gentleman who tried to stock his woods with
+    a nearly white variety; and when thus destroyed, they would in truth be
+    supplanted by, instead of being transformed into, the common rabbit. We
+    have seen that the feral rabbits of Jamaica, and especially of Porto
+    Santo, have assumed new colours and other new characters. The best
+    known case of reversion, and that on which the widely-spread belief in
+    its universality apparently rests, is that of pigs. These animals have
+    run wild in the West Indies, South America, and the Falkland Islands,
+    and have everywhere acquired the dark colour, the thick bristles, and
+    great tusks of the wild boar; and the young have reacquired
+    longitudinal stripes. But even in the case of the pig, Roulin describes
+    the half-wild animals in different parts of South America as differing
+    in several respects. In Louisiana the pig[76] has run wild, and is said
+    to differ a little in form, and much in colour, from the domestic
+    animal, yet does not closely resemble the wild boar of Europe. With
+    pigeons and fowls,[77] it is not known what variety was first turned
+    out, nor what character the feral birds have assumed. The guinea-fowl
+    in the West Indies, when feral, seems to vary more than in the
+    domesticated state.
+
+    With respect to plants run wild, Dr. Hooker[78] has strongly insisted
+    on what slight evidence the common belief in their power of reversion
+    rests. Godron[79] describes wild turnips, carrots, and celery; but
+    these plants in their cultivated state hardly differ from their wild
+    prototypes, except in the {34} succulency and enlargement of certain
+    parts,--characters which would be surely lost by plants growing in a
+    poor soil and struggling with other plants. No cultivated plant has run
+    wild on so enormous a scale as the cardoon (_Cynara cardunculus_) in La
+    Plata. Every botanist who has seen it growing there, in vast beds, as
+    high as a horse's back, has been struck with its peculiar appearance;
+    but whether it differs in any important point from the cultivated
+    Spanish form, which is said not to be prickly like its American
+    descendant, or whether it differs from he wild Mediterranean species,
+    which is said not to be social, I do not know.
+
+       *       *       *       *       *
+
+_Reversion to Characters derived from a Cross, in the case of
+Sub-varieties, Races, and Species._--When an individual having some
+recognizable peculiarity unites with another of the same sub-variety, not
+having the peculiarity in question, it often reappears in the descendants
+after an interval of several generations. Every one must have noticed, or
+heard from old people of children closely resembling in appearance or
+mental disposition, or in so small and complex a character as expression,
+one of their grandparents, or some more distant collateral relation. Very
+many anomalies of structure and diseases,[80] of which instances have been
+given in the last chapter, have come into a family from one parent, and
+have reappeared in the progeny after passing over two or three generations.
+The following case has been communicated to me on good authority, and may,
+I believe, be fully trusted: a pointer-bitch produced seven puppies; four
+were marked with blue and white, which is so unusual a colour with pointers
+that she was thought to have played false with one of the greyhounds, and
+the whole litter was condemned; but the gamekeeper was permitted to save
+one as a curiosity. Two years afterwards a friend of the owner saw the
+young dog, and declared that he was the image of his old pointer-bitch
+Sappho, the only blue and white pointer of pure descent which he had ever
+seen. This led to close inquiry, and it was proved that he was the
+great-great-grandson of Sappho; so that, according to the common
+expression, he had only 1-16th of her blood in his veins. Here it can
+hardly be doubted that a character derived from a cross with an individual
+of the same variety reappeared after passing over three generations.
+
+{35}
+
+When two distinct races are crossed, it is notorious that the tendency in
+the offspring to revert to one or both parent-forms is strong, and endures
+for many generations. I have myself seen the clearest evidence of this in
+crossed pigeons and with various plants. Mr. Sidney[81] states that, in a
+litter of Essex pigs, two young ones appeared which were the image of the
+Berkshire boar that had been used twenty-eight years before in giving size
+and constitution to the breed. I observed in the farmyard at Betley Hall
+some fowls showing a strong likeness to the Malay breed, and was told by
+Mr. Tollet that he had forty years before crossed his birds with Malays;
+and that, though he had at first attempted to get rid of this strain, he
+had subsequently given up the attempt in despair, as the Malay character
+would reappear.
+
+This strong tendency in crossed breeds to revert has given rise to endless
+discussions in how many generations after a single cross, either with a
+distinct breed or merely with an inferior animal, the breed may be
+considered as pure, and free from all danger of reversion. No one supposes
+that less than three generations suffices, and most breeders think that
+six, seven, or eight are necessary, and some go to still greater
+lengths.[82] But neither in the case of a breed which has been contaminated
+by a single cross, nor when, in the attempt to form an intermediate breed,
+half-bred animals have been matched together during many generations, can
+any rule be laid down how soon the tendency to reversion will be
+obliterated. It depends on the difference in the strength or prepotency of
+transmission in the two parent-forms, on their actual amount of difference,
+and on the nature of the conditions of life to which the crossed offspring
+are exposed. But we must be careful not to confound these cases of
+reversion to characters gained from a cross, with those given under the
+first class, in which characters originally common to _both_ parents, but
+lost at some former period, reappear; for such characters may recur after
+an almost indefinite number of generations.
+
+{36}
+
+The law of reversion is equally powerful with hybrids, when they are
+sufficiently fertile to breed together, or when they are repeatedly crossed
+with either pure parent-form, as with mongrels. It is not necessary to give
+instances, for in the case of plants almost every one who has worked on
+this subject from the time of Koelreuter to the present day has insisted on
+this tendency. Gaertner has recorded some good instances; but no one has
+given more striking cases than Naudin.[83] The tendency differs in degree
+or strength in different groups, and partly depends, as we shall presently
+see, on the fact of the parent-plants having been long cultivated. Although
+the tendency to reversion is extremely general with nearly all mongrels and
+hybrids, it cannot be considered as invariably characteristic of them;
+there is, also, reason to believe that it may be mastered by long-continued
+selection; but these subjects will more properly be discussed in a future
+chapter on Crossing. From what we see of the power and scope of reversion,
+both in pure races and when varieties or species are crossed, we may infer
+that characters of almost every kind are capable of reappearance after
+having been lost for a great length of time. But it does not follow from
+this that in each particular case certain characters will reappear: for
+instance, this will not occur when a race is crossed with another endowed
+with prepotency of transmission. In some few cases the power of reversion
+wholly fails, without our being able to assign any cause for the failure:
+thus it has been stated that in a French family in which 85 out of above
+600 members, during six generations, had been subject to night-blindness,
+"there has not been a single example of this affection in the children of
+parents who were themselves free from it."[84]
+
+       *       *       *       *       *
+
+_Reversion through Bud-propagation--Partial Reversion, by segments in the
+same flower or fruit, or in different parts of the {37} body in the same
+individual animal._--In the eleventh chapter, many cases of reversion by
+buds, independently of seminal generation, were given--as when a leaf-bud
+on a variegated, curled, or laciniated variety suddenly reassumes its
+proper character; or as when a Provence-rose appears on a moss-rose, or a
+peach on a nectarine-tree. In some of these cases only half the flower or
+fruit, or a smaller segment, or mere stripes, reassumed their former
+character; and here we have with buds reversion by segments. Vilmorin[85]
+has also recorded several cases with plants derived from seed, of flowers
+reverting by stripes or blotches to their primitive colours: he states that
+in all such cases a white or pale-coloured variety must first be formed,
+and, when this is propagated for a length of time by seed, striped
+seedlings occasionally make their appearance; and these can afterwards by
+care be multiplied by seed.
+
+The stripes and segments just referred to are not due, as far as is known,
+to reversion to characters derived from a cross, but to characters lost by
+variation. These cases, however, as Naudin[86] insists in his discussion on
+disjunction of character, are closely analogous with those given in the
+eleventh chapter, in which crossed plants are known to have produced
+half-and-half or striped flowers and fruit, or distinct kinds of flowers on
+the same root resembling the two parent-forms. Many piebald animals
+probably come under this same head. Such cases, as we shall see in the
+chapter on Crossing, apparently result from certain characters not readily
+blending together, and, as a consequence of this incapacity for fusion, the
+offspring either perfectly resemble one of their two parents, or resemble
+one parent in one part and the other parent in another part; or whilst
+young are intermediate in character, but with advancing age revert wholly
+or by segments to either parent-form, or to both. Thus young trees of the
+_Cytisus adami_ are intermediate in foliage and flowers between the two
+parent-forms; but when older the buds continually revert either partially
+or wholly to both forms. The cases given in the eleventh chapter on the
+changes which occurred during growth {38} in crossed plants of Tropaeolum,
+Cereus, Datura, and Lathyrus are all analogous. As however these plants are
+hybrids of the first generation, and as their buds after a time come to
+resemble their parents and not their grandparents, these cases do not at
+first appear to come under the law of reversion in the ordinary sense of
+the word; nevertheless, as the change is effected through a succession of
+bud-generations on the same plant, they may be thus included.
+
+Analogous facts have been observed in the animal kingdom, and are more
+remarkable, as they occur strictly in the same individual, and not as with
+plants through a succession of bud-generations. With animals the act of
+reversion, if it can be so designated, does not pass over a true
+generation, but merely over the early stages of growth in the same
+individual. For instance, I crossed several white hens with a black cock,
+and many of the chickens were during the first year perfectly white, but
+acquired during the second year black feathers; on the other hand, some of
+the chickens which were at first black became during the second year
+piebald with white. A great breeder[87] says, that a Pencilled Brahma hen
+which has any of the blood of the Light Brahma in her, will "occasionally
+produce a pullet well pencilled during the first year, but she will most
+likely moult brown on the shoulders and become quite unlike her original
+colours in the second year." The same thing occurs with Light Brahmas if of
+impure blood. I have observed exactly similar cases with the crossed
+offspring from differently coloured pigeons. But here is a more remarkable
+fact: I crossed a turbit, which has a frill formed by the feathers being
+reversed on its breast, with a trumpeter; and one of the young pigeons thus
+raised showed at first not a trace of the frill, but, after moulting
+thrice, a small yet unmistakably distinct frill appeared on its breast.
+According to Girou,[88] calves produced from a red cow by a black bull, or
+from a black cow by a red bull, are not rarely born red, and subsequently
+become black.
+
+In the foregoing cases, the characters which appear with advancing age are
+the result of a cross in the previous or some {39} former generation; but
+in the following cases, the characters which thus reappear formerly
+appertained to the species, and were lost at a more or less remote epoch.
+Thus, according to Azara,[89] the calves of a hornless race of cattle which
+originated in Corrientes, though at first quite hornless, as they become
+adult sometimes acquire small, crooked, and loose horns; and these in
+succeeding years occasionally become attached to the skull. White and black
+bantams, both of which generally breed true, sometimes assume as they grow
+old a saffron or red plumage. For instance, a first-rate black bantam has
+been described, which during three seasons was perfectly black, but then
+annually became more and more red; and it deserves notice that this
+tendency to change, whenever it occurs in a bantam, "is almost certain to
+prove hereditary."[90] The cuckoo or blue-mottled Dorking cock, when old,
+is liable to acquire yellow or orange hackles in place of his proper
+bluish-grey hackles.[91] Now, as _Gallus bankiva_ is coloured red and
+orange, and as Dorking fowls and both kinds of bantams are descended from
+this species, we can hardly doubt that the change which occasionally occurs
+in the plumage of these birds as their age advances, results from a
+tendency in the individual to revert to the primitive type.
+
+       *       *       *       *       *
+
+_Crossing as a direct cause of Reversion._--It has long been notorious that
+hybrids and mongrels often revert to both or to one of their parent-forms,
+after an interval of from two to seven or eight, or according to some
+authorities even a greater number of generations. But that the act of
+crossing in itself gives an impulse towards reversion, as shown by the
+reappearance of long-lost characters, has never, I believe, been hitherto
+proved. The proof lies in certain peculiarities, which do not characterise
+the immediate parents, and therefore cannot have been derived from them,
+frequently appearing in the offspring of two breeds when crossed, which
+peculiarities never appear, or appear with extreme rarity, in these same
+breeds, as long as they are {40} precluded from crossing. As this
+conclusion seems to me highly curious and novel, I will give the evidence
+in detail.
+
+    My attention was first called to this subject, and I was led to make
+    numerous experiments, by MM. Boitard and Corbie having stated that,
+    when they crossed certain breeds, pigeons coloured like the wild _C.
+    livia_, or the common dovecot, namely, slaty-blue, with double black
+    wing-bars, sometimes chequered with black, white loins, the tail barred
+    with black, with the outer feathers edged with white, were almost
+    invariably produced. The breeds which I crossed, and the remarkable
+    results attained, have been fully described in the sixth chapter. I
+    selected pigeons, belonging to true and ancient breeds, which had not a
+    trace of blue or any of the above specified marks; but when crossed,
+    and their mongrels recrossed, young birds were continually produced,
+    more or less plainly coloured slaty-blue, with some or all of the
+    proper characteristic marks. I may recall to the reader's memory one
+    case, namely, that of a pigeon, hardly distinguishable from the wild
+    Shetland species, the grandchild of a red-spot, white fantail, and two
+    black barbs, from any of which, when purely-bred, the production of a
+    pigeon coloured like the wild _C. livia_ would have been almost a
+    prodigy.
+
+    I was thus led to make the experiments, recorded in the seventh
+    chapter, on fowls. I selected long-established, pure breeds, in which
+    there was not a trace of red, yet in several of the mongrels feathers
+    of this colour appeared; and one magnificent bird, the offspring of a
+    black Spanish cock and white Silk hen, was coloured almost exactly like
+    the wild _Gallus bankiva_. All who know anything of the breeding of
+    poultry will admit that tens of thousands of pure Spanish and of pure
+    white Silk fowls might have been reared without the appearance of a red
+    feather. The fact, given on the authority of Mr. Tegetmeier, of the
+    frequent appearance, in mongrel fowls, of pencilled or
+    transversely-barred feathers, like those common to many gallinaceous
+    birds, is likewise apparently a case of reversion to a character
+    formerly possessed by some ancient progenitor of the family. I owe to
+    the kindness of this same excellent observer the inspection of some
+    neck-hackles and tail-feathers from a hybrid between the common fowl
+    and a very distinct species, the _Gallus varius_; and these feathers
+    are transversely striped in a conspicuous manner with dark metallic
+    blue and grey, a character which could not have been derived from
+    either immediate parent.
+
+    I have been informed by Mr. B. P. Brent, that he crossed a white
+    Aylesbury drake and a black so-called Labrador duck, both of which are
+    true breeds, and he obtained a young drake closely like the mallard
+    (_A. boschas_). Of the musk-duck (_A. moschata_, Linn.) there are two
+    sub-breeds, namely, white and slate-coloured; and these I am informed
+    breed true, or nearly true. But the Rev. W. D. Fox tells me that, by
+    putting a white drake to a slate-coloured duck, black birds, pied with
+    white, like the wild musk-duck, were always produced.
+
+    We have seen in the fourth chapter, that the so-called Himalayan
+    rabbit, with its snow-white body, black ears, nose, tail, and feet,
+    breeds {41} perfectly true. This race is known to have been formed by
+    the union of two varieties of silver-grey rabbits. Now, when a
+    Himalayan doe was crossed by a sandy-coloured buck, a silver-grey
+    rabbit was produced; and this is evidently a case of reversion to one
+    of the parent varieties. The young of the Himalayan rabbit are born
+    snow-white, and the dark marks do not appear until some time
+    subsequently; but occasionally young Himalayan rabbits are born of a
+    light silver-grey, which colour soon disappears; so that here we have a
+    trace of reversion, during an early period of life, to the
+    parent-varieties, independently of any recent cross.
+
+    In the third chapter is was shown that at an ancient period some breeds
+    of cattle in the wilder parts of Britain were white with dark ears, and
+    that the cattle now kept half wild in certain parks, and those which
+    have run quite wild in two distant parts of the world, are likewise
+    thus coloured. Now, an experienced breeder, Mr. J. Beasley, of
+    Northamptonshire,[92] crossed some carefully selected West Highland
+    cows with purely-bred shorthorn bulls. The bulls were red, red and
+    white, or dark roan; and the Highland cows were all of a red colour,
+    inclining to a light or yellow shade. But a considerable number of the
+    offspring--and Mr. Beasley calls attention to this as a remarkable
+    fact--were white, or white with red ears. Bearing in mind that none of
+    the parents were white, and that they were purely-bred animals, it is
+    highly probable that here the offspring reverted, in consequence of the
+    cross, to the colour either of the aboriginal parent-species or of some
+    ancient and half-wild parent-breed. The following case, perhaps, comes
+    under the same head: cows in their natural state have their udders but
+    little developed, and do not yield nearly so much milk as our
+    domesticated animals. Now there is some reason to believe[93] that
+    cross-bred animals between two kinds, both of which are good milkers,
+    such as Alderneys and Shorthorns, often turn out worthless in this
+    respect.
+
+    In the chapter on the Horse reasons were assigned for believing that
+    the primitive stock was striped and dun-coloured; and details were
+    given, showing that in all parts of the world stripes of a dark colour
+    frequently appear along the spine, across the legs, and on the
+    shoulders, where they are occasionally double or treble, and even
+    sometimes on the face and body of horses of all breeds and of all
+    colours. But the stripes appear most frequently on the various kinds of
+    duns. They may sometimes plainly be seen on foals, and subsequently
+    disappear. The dun-colour and the stripes are strongly transmitted when
+    a horse thus characterised is crossed with any other; but I was not
+    able to prove that striped duns are generally produced from the
+    crossing of two distinct breeds, neither of which are duns, though this
+    does sometimes occur.
+
+    The legs of the ass are often striped, and this may be considered as a
+    reversion to the wild parent-form, the _Asinus taeniopus_ of
+    Abyssinia,[94] which is thus striped. In the domestic animal the
+    stripes on the shoulder are occasionally double, or forked at the
+    extremity, as in certain zebrine {42} species. There is reason to
+    believe that the foal is frequently more plainly striped on the legs
+    than the adult animal. As with the horse, I have not acquired any
+    distinct evidence that the crossing of differently-coloured varieties
+    of the ass brings out the stripes.
+
+    But now let us turn to the result of crossing the horse and ass.
+    Although mules are not nearly so numerous in England as asses, I have
+    seen a much greater number with striped legs, and with the stripes far
+    more conspicuous than in either parent-form. Such mules are generally
+    light-coloured, and might be called fallow-duns. The shoulder-stripe in
+    one instance was deeply forked at the extremity, and in another
+    instance was double, though united in the middle. Mr. Martin gives a
+    figure of a Spanish mule with strong zebra-like marks on its legs,[95]
+    and remarks, that mules are particularly liable to be thus striped on
+    their legs. In South America, according to Roulin,[96] such stripes are
+    more frequent and conspicuous in the mule than in the ass. In the
+    United States, Mr. Gosse,[97] speaking of these animals, says, "that in
+    a great number, perhaps in nine out of every ten, the legs are banded
+    with transverse dark stripes."
+
+    Many years ago I saw in the Zoological Gardens a curious triple hybrid,
+    from a bay mare, by a hybrid from a male ass and female zebra. This
+    animal when old had hardly any stripes; but I was assured by the
+    superintendent, that when young it had shoulder-stripes, and faint
+    stripes on its flanks and legs. I mention this case more especially as
+    an instance of the stripes being much plainer during youth than in old
+    age.
+
+    As the zebra has such conspicuously striped legs, it might have been
+    expected that the hybrids from this animal and the common ass would
+    have had their legs in some degree striped; but it appears from the
+    figures given in Dr. Gray's 'Knowsley Gleanings,' and still more
+    plainly from that given by Geoffroy and F. Cuvier,[98] that the legs
+    are much more conspicuously striped than the rest of the body; and this
+    fact is intelligible only on the belief that the ass aids in giving,
+    through the power of reversion, this character to its hybrid offspring.
+
+    The quagga is banded over the whole front part of its body like a
+    zebra, but has no stripes on its legs, or mere traces of them. But in
+    the famous hybrid bred by Lord Morton,[99] from a chesnut, nearly
+    purely-bred, Arabian mare, by a male quagga, the stripes were "more
+    strongly defined and darker than those on the legs of the quagga." The
+    mare was subsequently put to a black Arabian horse, and bore two colts,
+    both of which, as formerly stated, were plainly striped on the legs,
+    and one of them likewise had stripes on the neck and body.
+
+    The _Asinus Indicus_[100] is characterised by a spinal stripe, without
+    shoulder {43} or leg stripes; but traces of these latter stripes may
+    occasionally be seen even in the adult;[101] and Colonel S. Poole, who
+    has had ample opportunities for observation, informs me that in the
+    foal, when first born, the head and legs are often striped, but the
+    shoulder-stripe is not so distinct as in the domestic ass; all these
+    stripes, excepting that along the spine, soon disappear. Now a hybrid,
+    raised at Knowsley[102] from a female of this species by a male
+    domestic ass, had all four legs transversely and conspicuously striped,
+    had three short stripes on each shoulder, and had even some zebra-like
+    stripes on its face! Dr. Gray informs me that he has seen a second
+    hybrid of the same parentage similarly striped.
+
+From these facts we see that the crossing of the several equine species
+tends in a marked manner to cause stripes to appear on various parts of the
+body, especially on the legs. As we do not know whether the primordial
+parent of the genus was striped, the appearance of the stripes can only
+hypothetically be attributed to reversion. But most persons, after
+considering the many undoubted cases of variously coloured marks
+reappearing by reversion in crossed pigeons, fowls, ducks, &c., will come
+to the same conclusion with respect to the horse-genus; and in this case we
+must admit that the progenitor of the group was striped on the legs,
+shoulders, face, and probably over the whole body, like a zebra. If we
+reject this view, the frequent and almost regular appearance of stripes in
+the several foregoing hybrids is left without any explanation.
+
+       *       *       *       *       *
+
+It would appear that with crossed animals a similar tendency to the
+recovery of lost characters holds good even with instincts. There are some
+breeds of fowls which are called "everlasting layers," because they have
+lost the instinct of incubation; and so rare is it for them to incubate
+that I have seen notices published in works on poultry, when hens of such
+breeds have taken to sit.[103] Yet the aboriginal species was of course a
+good incubator; for with birds in a state of nature hardly any {44}
+instinct is so strong as this. Now, so many cases have been recorded of the
+crossed offspring from two races, neither of which are incubators, becoming
+first-rate sitters, that the reappearance of this instinct must be
+attributed to reversion from crossing. One author goes so far as to say,
+"that a cross between two non-sitting varieties almost invariably produces
+a mongrel that becomes broody, and sits with remarkable steadiness."[104]
+Another author, after giving a striking example, remarks that the fact can
+be explained only on the principle that "two negatives make a positive." It
+cannot, however, be maintained that hens produced from a cross between two
+non-sitting breeds invariably recover their lost instinct, any more than
+that crossed fowls or pigeons invariably recover the red or blue plumage of
+their prototypes. I raised several chickens from a Polish hen by a Spanish
+cock,--breeds which do not incubate,--and none of the young hens at first
+recovered their instinct, and this appeared to afford a well-marked
+exception to the foregoing rule; but one of these hens, the only one which
+was preserved, in the third year sat well on her eggs and reared a brood of
+chickens. So that here we have the appearance with advancing age of a
+primitive instinct, in the same manner as we have seen that the red plumage
+of the _Gallus bankiva_ is sometimes reacquired by crossed and purely-bred
+fowls of various kinds as they grow old.
+
+The parents of all our domesticated animals were of course aboriginally
+wild in disposition; and when a domesticated species is crossed with a
+distinct species, whether this is a domesticated or only tamed animal, the
+hybrids are often wild {45} to such a degree, that the fact is intelligible
+only on the principle that the cross has caused a partial return to the
+primitive disposition.
+
+The Earl of Powis formerly imported some thoroughly domesticated humped
+cattle from India, and crossed them with English breeds, which belong to a
+distinct species; and his agent remarked to me, without any question having
+been asked, how oddly wild the cross-bred animals were. The European wild
+boar and the Chinese domesticated pig are almost certainly specifically
+distinct: Sir F. Darwin crossed a sow of the latter breed with a wild
+Alpine boar which had become extremely tame, but the young, though having
+half-domesticated blood in their veins, were "extremely wild in
+confinement, and would not eat swill like common English pigs." Mr. Hewitt,
+who has had great experience in crossing tame cock-pheasants with fowls
+belonging to five breeds, gives as the character of all "extraordinary
+wildness;"[105] but I have myself seen one exception to this rule. Mr.
+S. J. Salter,[106] who raised a large number of hybrids from a bantam-hen
+by _Gallus Sonneratii_, states that "all were exceedingly wild." Mr.
+Waterton[107] bred some wild ducks from eggs hatched under a common duck,
+and the young were allowed to cross freely both amongst themselves and with
+the tame ducks; they were "half wild and half tame; they came to the
+windows to be fed, but still they had a wariness about them quite
+remarkable."
+
+On the other hand, mules from the horse and ass are certainly not in the
+least wild, yet they are notorious for obstinacy and vice. Mr. Brent, who
+has crossed canary-birds with many kinds of finches, has not observed, as
+he informs me, that the hybrids were in any way remarkably wild. Hybrids
+are often raised between the common and musk duck, and I have been assured
+by three persons, who have kept these crossed birds, that they were not
+wild; but Mr. Garnett[108] observed that his female hybrids exhibited
+"migratory propensities," of which there is not a vestige in the common or
+musk duck. No case is {46} known of this latter bird having escaped and
+become wild in Europe or Asia, except, according to Pallas, on the Caspian
+Sea; and the common domestic duck only occasionally becomes wild in
+districts where large lakes and fens abound. Nevertheless, a large number
+of cases have been recorded[109] of hybrids from these two ducks, although
+so few are reared in comparison with purely-bred birds of either species,
+having been shot in a completely wild state. It is improbable that any of
+these hybrids could have acquired their wildness from the musk-duck having
+paired with a truly wild duck; and this is known not to be the case in
+North America; hence we must infer that they have reacquired, through
+reversion, their wildness, as well as renewed powers of flight.
+
+These latter facts remind us of the statements, so frequently made by
+travellers in all parts of the world, on the degraded state and savage
+disposition of crossed races of man. That many excellent and kind-hearted
+mulattos have existed no one will dispute; and a more mild and gentle set
+of men could hardly be found than the inhabitants of the island of Chiloe,
+who consist of Indians commingled with Spaniards in various proportions. On
+the other hand, many years ago, long before I had thought of the present
+subject, I was struck with the fact that, in South America, men of
+complicated descent between Negroes, Indians, and Spaniards, seldom had,
+whatever the cause might be, a good expression.[110] Livingstone,--and a
+more unimpeachable authority cannot be quoted,--after speaking of a
+half-caste man on the Zambesi, described by the Portuguese as a rare
+monster of inhumanity, remarks, "It is unaccountable why half-castes, such
+as he, are so much more cruel than the Portuguese, but such is undoubtedly
+the case." An inhabitant remarked to Livingstone, "God made white men, and
+God made black men, but the Devil made half-castes."[111] When two races,
+both {47} low in the scale, are crossed, the progeny seems to be eminently
+bad. Thus the noble-hearted Humboldt, who felt none of that prejudice
+against the inferior races now so current in England, speaks in strong
+terms of the bad and savage disposition of Zambos, or half-castes between
+Indians and Negroes; and this conclusion has been arrived at by various
+observers.[112] From these facts we may perhaps infer that the degraded
+state of so many half-castes is in part due to reversion to a primitive and
+savage condition, induced by the act of crossing, as well as to the
+unfavourable moral conditions under which they generally exist.
+
+       *       *       *       *       *
+
+_Summary on the proximate causes leading to Reversion._--When purely-bred
+animals or plants reassume long-lost characters,--when the common ass, for
+instance, is born with striped legs, when a pure race of black or white
+pigeons throws a slaty-blue bird, or when a cultivated heartsease with
+large and rounded flowers produces a seedling with small and elongated
+flowers,--we are quite unable to assign any proximate cause. When animals
+run wild, the tendency to reversion, which, though it has been greatly
+exaggerated, no doubt exists, is sometimes to a certain extent
+intelligible. Thus, with feral pigs, exposure to the weather will probably
+favour the growth of the bristles, as is known to be the case with the hair
+of other domesticated animals, and through correlation the tusks will tend
+to be redeveloped. But the reappearance of coloured longitudinal stripes on
+young feral pigs cannot be attributed to the direct action of external
+conditions. In this case, and in many others, we can only say that changed
+habits of life apparently have favoured a tendency, inherent or latent in
+the species, to return to the primitive state.
+
+It will be shown in a future chapter that the position of flowers on the
+summit of the axis, and the position of seeds within the capsule, sometimes
+determine a tendency towards reversion; and this apparently depends on the
+amount of sap or nutriment which the flower-buds and seeds receive. The
+position, also, of buds, either on branches or on roots, sometimes
+determines, as was formerly shown, the transmission of the {48} proper
+character of the variety, or its reversion to a former state.
+
+We have seen in the last section that when two races or species are crossed
+there is the strongest tendency to the reappearance in the offspring of
+long-lost characters, possessed by neither parent nor immediate progenitor.
+When two white, or red, or black pigeons, of well-established breeds, are
+united, the offspring are almost sure to inherit the same colours; but when
+differently-coloured birds are crossed, the opposed forces of inheritance
+apparently counteract each other, and the tendency which is inherent in
+both parents to produce slaty-blue offspring becomes predominant. So it is
+in several other cases. But when, for instance, the ass is crossed with _A.
+Indicus_ or with the horse,--animals which have not striped legs,--and the
+hybrids have conspicuous stripes on their legs and even on their faces, all
+that can be said is, that an inherent tendency to reversion is evolved
+through some disturbance in the organisation caused by the act of crossing.
+
+Another form of reversion is far commoner, indeed is almost universal with
+the offspring from a cross, namely, to the characters proper to either pure
+parent-form. As a general rule, crossed offspring in the first generation
+are nearly intermediate between their parents, but the grandchildren and
+succeeding generations continually revert, in a greater or lesser degree,
+to one or both of their progenitors. Several authors have maintained that
+hybrids and mongrels include all the characters of both parents, not fused
+together, but merely mingled in different proportions in different parts of
+the body; or, as Naudin[113] has expressed it, a hybrid is a living
+mosaic-work, in which the eye cannot distinguish the discordant elements,
+so completely are they intermingled. We can hardly doubt that, in a certain
+sense, this is true, as when we behold in a hybrid the elements of both
+species segregating themselves into segments in the same flower or fruit,
+by a process of self-attraction or self-affinity; this segregation taking
+place either by seminal or by bud-propagation. Naudin further believes that
+the segregation of the two specific elements or essences is eminently
+liable to occur in the male and female reproductive matter; and he thus
+explains the almost {49} universal tendency to reversion in successive
+hybrid generations. For this would be the natural result of the union of
+pollen and ovules, in both of which the elements of the same species had
+been segregated by self-affinity. If, on the other hand, pollen which
+included the elements of one species happened to unite with ovules
+including the elements of the other species, the intermediate or hybrid
+state would still be retained, and there would be no reversion. But it
+would, as I suspect, be more correct to say that the elements of both
+parent-species exist in every hybrid in a double state, namely, blended
+together and completely separate. How this is possible, and what the term
+specific essence or element may be supposed to express, I shall attempt to
+show in the hypothetical chapter on pangenesis.
+
+But Naudin's view, as propounded by him, is not applicable to the
+reappearance of characters lost long ago by variation; and it is hardly
+applicable to races or species which, after having been crossed at some
+former period with a distinct form, and having since lost all traces of the
+cross, nevertheless occasionally yield an individual which reverts (as in
+the case of the great-great-grandchild of the pointer Sappho) to the
+crossing form. The most simple case of reversion, namely, of a hybrid or
+mongrel to its grandparents, is connected by an almost perfect series with
+the extreme case of a purely-bred race recovering characters which had been
+lost during many ages; and we are thus led to infer that all the cases must
+be related by some common bond.
+
+Gaertner believed that only those hybrid plants which are highly sterile
+exhibit any tendency to reversion to their parent-forms. It is rash to
+doubt so good an observer, but this conclusion must I think be an error;
+and it may perhaps be accounted for by the nature of the genera observed by
+him, for he admits that the tendency differs in different genera. The
+statement is also directly contradicted by Naudin's observations, and by
+the notorious fact that perfectly fertile mongrels exhibit the tendency in
+a high degree,--even in a higher degree, according to Gaertner himself,
+than hybrids.[114]
+
+Gaertner further states that reversions rarely occur with {50} hybrid
+plants raised from species which have not been cultivated, whilst, with
+those which have been long cultivated, they are of frequent occurrence.
+This conclusion explains a curious discrepancy: Max Wichura,[115] who
+worked exclusively on willows, which had not been subjected to culture,
+never saw an instance of reversion; and he goes so far as to suspect that
+the careful Gaertner had not sufficiently protected his hybrids from the
+pollen of the parent-species: Naudin, on the other hand, who chiefly
+experimented on cucurbitaceous and other cultivated plants, insists more
+strenuously than any other author on the tendency to reversion in all
+hybrids. The conclusion that the condition of the parent-species, as
+affected by culture, is one of the proximate causes leading to reversion,
+agrees fairly well with the converse case of domesticated animals and
+cultivated plants being liable to reversion when they become feral; for in
+both cases the organisation or constitution must be disturbed, though in a
+very different way.
+
+Finally, we have seen that characters often reappear in purely-bred races
+without our being able to assign any proximate cause; but when they become
+feral this is either indirectly or directly induced by the change in their
+conditions of life. With crossed breeds, the act of crossing in itself
+certainly leads to the recovery of long-lost characters, as well as of
+those derived from either parent-form. Changed conditions, consequent on
+cultivation, and the relative position of buds, flowers, and seeds on the
+plant, all apparently aid in giving this same tendency. Reversion may occur
+either through seminal or bud generation, generally at birth, but sometimes
+only with an advance of age. Segments or portions of the individual may
+alone be thus affected. That a being should be born resembling in certain
+characters an ancestor removed by two or three, and in some cases by
+hundreds or even thousands of generations, is assuredly a wonderful fact.
+In these cases the child is commonly said to inherit such characters
+directly from its grandparents or more remote ancestors. But this view is
+hardly conceivable. If, however, we suppose that every character is derived
+{51} exclusively from the father or mother, but that many characters lie
+latent in both parents during a long succession of generations, the
+foregoing facts are intelligible. In what manner characters may be
+conceived to lie latent, will be considered in a future chapter to which I
+have lately alluded.
+
+       *       *       *       *       *
+
+_Latent Characters._--But I must explain what is meant by characters lying
+latent. The most obvious illustration is afforded by secondary sexual
+characters. In every female all the secondary male characters, and in every
+male all the secondary female characters, apparently exist in a latent
+state, ready to be evolved under certain conditions. It is well known that
+a large number of female birds, such as fowls, various pheasants,
+partridges, peahens, ducks, &c., when old or diseased, or when operated on,
+partly assume the secondary male characters of their species. In the case
+of the hen-pheasant this has been observed to occur far more frequently
+during certain seasons than during others.[116] A duck ten years old has
+been known to assume both the perfect winter and summer plumage of the
+drake.[117] Waterton[118] gives a curious case of a hen which had ceased
+laying, and had assumed the plumage, voice, spurs, and warlike disposition
+of the cock; when opposed to an enemy she would erect her hackles and show
+fight. Thus every character, even to the instinct and manner of fighting,
+must have lain dormant in this hen as long as her ovaria continued to act.
+The females of two kinds of deer, when old, have been known to acquire
+horns; and, as Hunter has remarked, we see something of an analogous nature
+in the human species.
+
+On the other hand, with male animals, it is notorious that the secondary
+sexual characters are more or less completely lost when they are subjected
+to castration. Thus, if the operation be performed on a young cock, he
+never, as Yarrell states, crows {52} again; the comb, wattles, and spurs do
+not grow to their full size, and the hackles assume an intermediate
+appearance between true hackles and the feathers of the hen. Cases are
+recorded of confinement alone causing analogous results. But characters
+properly confined to the female are likewise acquired; the capon takes to
+sitting on eggs, and will bring up chickens; and what is more curious, the
+utterly sterile male hybrids from the pheasant and the fowl act in the same
+manner, "their delight being to watch when the hens leave their nests, and
+to take on themselves the office of a sitter."[119] That admirable observer
+Reaumur[120] asserts that a cock, by being long confined in solitude and
+darkness, can be taught to take charge of young chickens; he then utters a
+peculiar cry, and retains during his whole life this newly acquired
+maternal instinct. The many well-ascertained cases of various male mammals
+giving milk, show that their rudimentary mammary glands retain this
+capacity in a latent condition.
+
+We thus see that in many, probably in all cases, the secondary characters
+of each sex lie dormant or latent in the opposite sex, ready to be evolved
+under peculiar circumstances. We can thus understand how, for instance, it
+is possible for a good milking cow to transmit her good qualities through
+her male offspring to future generations; for we may confidently believe
+that these qualities are present, though latent, in the males of each
+generation. So it is with the game-cock, who can transmit his superiority
+in courage and vigour through his female to his male offspring; and with
+man it is known [121] that diseases, such as hydrocele, necessarily
+confined to the male sex, can be transmitted through the female to the
+grandson. Such cases as these offer, as was remarked at the commencement of
+this chapter, the simplest possible examples of reversion; and they are
+intelligible on the belief that characters common to the grandparent and
+grandchild of the same sex are present, though latent, in the intermediate
+parent of the opposite sex.
+
+The subject of latent characters is so important, as we shall see in a
+future chapter, that I will give another illustration. {53} Many animals
+have the right and left sides of their body unequally developed: this is
+well known to be the case with flat-fish, in which the one side differs in
+thickness and colour, and in the shape of the fins, from the other; and
+during the growth of the young fish one eye actually travels, as shown by
+Steenstrup, from the lower to the upper surface.[122] In most flat-fishes
+the left is the blind side, but in some it is the right; though in both
+cases "wrong fishes," which are developed in a reversed manner to what is
+usual, occasionally occur, and in _Platessa flesus_ the right or left side
+is indifferently developed, the one as often as the other. With gasteropods
+or shell-fish, the right and left sides are extremely unequal; the far
+greater number of species are dextral, with rare and occasional reversals
+of development, and some few are normally sinistral; but certain species of
+Bulimus, and, many Achatinellae,[123] are as often sinistral as dextral. I
+will give an analogous case in the great Articulate kingdom: the two sides
+of Verruca[124] are so wonderfully unlike, that without careful dissection
+it is extremely difficult to recognise the corresponding parts on the
+opposite sides of the body; yet it is apparently a mere matter of chance
+whether it be the right or the left side that undergoes so singular an
+amount of change. One plant is known to me[125] in which the flower,
+according as it stands on the one or other side of the spike, is unequally
+developed. In all the foregoing cases the two sides of the animal are
+perfectly symmetrical at an early period of growth. Now, whenever a species
+is as liable to be unequally developed on the one as on the other side, we
+may infer that the capacity for such development is present, though latent,
+in the undeveloped side. And as a reversal of development occasionally
+occurs in animals of many kinds, this latent capacity is probably very
+common.
+
+The best yet simplest instances of characters lying dormant are, perhaps,
+those previously given, in which chickens and {54} young pigeons, raised
+from a cross between differently coloured birds, are at first of one
+colour, but in a year or two acquire feathers of the colour of the other
+parent; for in this case the tendency to a change of plumage is clearly
+latent in the young bird. So it is with hornless breeds of cattle, some of
+which acquire, as they grow old, small horns. Purely bred black and white
+bantams, and some other fowls, occasionally assume, with advancing years,
+the red feathers of the parent-species. I will here add a somewhat
+different case, as it connects in a striking manner latent characters of
+two classes. Mr. Hewitt[126] possessed an excellent Sebright gold-laced hen
+bantam, which, as she became old, grew diseased in her ovaria, and assumed
+male characters. In this breed the males resemble the females in all
+respects except in their combs, wattles, spurs, and instincts; hence it
+might have been expected that the diseased hen would have assumed only
+those masculine characters which are proper to the breed, but she acquired,
+in addition, well-arched tail sickle-feathers quite a foot in length,
+saddle-feathers on the loins, and hackles on the neck,--ornaments which, as
+Mr. Hewitt remarks, "would be held as abominable in this breed." The
+Sebright bantam is known[127] to have originated about the year 1800 from a
+cross between a common bantam and a Polish fowl, recrossed by a hen-tailed
+bantam, and carefully selected; hence there can hardly be a doubt that the
+sickle-feathers and hackles which appeared in the old hen were derived from
+the Polish fowl or common bantam; and we thus see that not only certain
+masculine characters proper to the Sebright bantam, but other masculine
+characters derived from the first progenitors of the breed, removed by a
+period of above sixty years, were lying latent in this hen-bird, ready to
+be evolved as soon as her ovaria became diseased.
+
+From these several facts it must be admitted that certain characters,
+capacities, and instincts may lie latent in an individual, and even in a
+succession of individuals, without our being able to detect the least signs
+of their presence. We have {55} already seen that the transmission of a
+character from the grandparent to the grandchild, with its apparent
+omission in the intermediate parent of the opposite sex, becomes simple on
+this view. When fowls, pigeons, or cattle of different colours are crossed,
+and their offspring change colour as they grow old, or when the crossed
+turbit acquired the characteristic frill after its third moult, or when
+purely-bred bantams partially assume the red plumage of their prototype, we
+cannot doubt that these qualities were from the first present, though
+latent, in the individual animal, like the characters of a moth in the
+caterpillar. Now, if these animals had produced offspring before they had
+acquired with advancing age their new characters, nothing is more probable
+than that they would have transmitted them to some of their offspring,
+which in this case would in appearance have received such characters from
+their grandparents or more distant progenitors. We should then have had a
+case of reversion, that is, of the reappearance in the child of an
+ancestral character, actually present, though during youth completely
+latent, in the parent; and this we may safely conclude is what occurs with
+reversions of all kinds to progenitors however remote.
+
+This view of the latency in each generation of all the characters which
+appear through reversion, is also supported by their actual presence in
+some cases during early youth alone, or by their more frequent appearance
+and greater distinctness at this age than during maturity. We have seen
+that this is often the case with the stripes on the legs and faces of the
+several species of the horse-genus. The Himalayan rabbit, when crossed,
+sometimes produces offspring which revert to the parent silver-grey breed,
+and we have seen that in purely bred animals pale-grey fur occasionally
+reappears during early youth. Black cats, we may feel assured, would
+occasionally produce by reversion tabbies; and on young black kittens, with
+a pedigree[128] known to have been long pure, faint traces of stripes may
+almost always be seen which afterwards disappear. Hornless Suffolk cattle
+occasionally produce by reversion horned animals; and Youatt[129] asserts
+that even in hornless individuals {56} "the rudiment of a horn may be often
+felt at an early age."
+
+No doubt it appears at first sight in the highest degree improbable that in
+every horse of every generation there should be a latent capacity and
+tendency to produce stripes, though these may not appear once in a thousand
+generations; that in every white, black, or other coloured pigeon, which
+may have transmitted its proper colour during centuries, there should be a
+latent capacity in the plumage to become blue and to be marked with certain
+characteristic bars; that in every child in a six-fingered family there
+should be the capacity for the production of an additional digit; and so in
+other cases. Nevertheless there is no more inherent improbability in this
+being the case than in a useless and rudimentary organ, or even in only a
+tendency to the production of a rudimentary organ, being inherited during
+millions of generations, as is well known to occur with a multitude of
+organic beings. There is no more inherent improbability in each domestic
+pig, during a thousand generations, retaining the capacity and tendency to
+develop great tusks under fitting conditions, than in the young calf having
+retained for an indefinite number of generations rudimentary incisor teeth,
+which never protrude through the gums.
+
+I shall give at the end of the next chapter a summary of the three
+preceding chapters; but as isolated and striking cases of reversion have
+here been chiefly insisted on, I wish to guard the reader against supposing
+that reversion is due to some rare or accidental combination of
+circumstances. When a character, lost during hundreds of generations,
+suddenly reappears, no doubt some such combination must occur; but
+reversions may be constantly observed, at least to the immediately
+preceding generations, in the offspring of most unions. This has been
+universally recognised in the case of hybrids and mongrels, but it has been
+recognised simply from the difference between the united forms rendering
+the resemblance of the offspring to their grandparents or more remote
+progenitors of easy detection. Reversion is likewise almost invariably the
+rule, as Mr. Sedgwick has shown, with certain diseases. Hence we must
+conclude that a tendency to this peculiar form of transmission is an
+integral part of the general law of inheritance. {57}
+
+       *       *       *       *       *
+
+_Monstrosities._--A large number of monstrous growths and of lesser
+anomalies are admitted by every one to be due to an arrest of development,
+that is to the persistence of an embryonic condition. If every horse or ass
+had striped legs whilst young, the stripes which occasionally appear on
+these animals when adult would have to be considered as due to the
+anomalous retention of an early character, and not as due to reversion.
+Now, the leg-stripes in the horse-genus, and some other characters in
+analogous cases, are apt to occur during early youth and then to disappear;
+thus the persistence of early characters and reversion are brought into
+close connexion.
+
+But many monstrosities can hardly be considered as the result of an arrest
+of development; for parts of which no trace can be detected in the embryo,
+but which occur in other members of the same class of animals or plants,
+occasionally appear, and these may probably with truth be attributed to
+reversion. For instance: supernumerary mammae, capable of secreting milk,
+are not extremely rare in women; and as many as five have been observed.
+When four are developed, they are generally arranged symmetrically on each
+side of the chest; and in one instance a woman (the daughter of another
+with supernumerary mammae) had one mamma, which yielded milk, developed in
+the inguinal region. This latter case, when we remember the position of the
+mammae in some of the lower animals on both the chest and inguinal region,
+is highly remarkable, and leads to the belief that in all cases the
+additional mammae in woman are due to reversion. The facts given in the
+last chapter on the tendency in supernumerary digits to regrowth after
+amputation, indicate their relation to the digits of the lower vertebrate
+animals, and lead to the suspicion that their appearance may in some manner
+be connected with reversion. But I shall have to recur, in the chapter on
+pangenesis, to the abnormal multiplication of organs, and likewise to their
+occasional transposition. The occasional development in man of the
+coccygeal vertebrae into a short and free tail, though it thus becomes in
+one sense more perfectly developed, may at the same time be considered as
+an arrest of development, and as a case of reversion. The greater frequency
+of a monstrous kind of proboscis in the pig than in any other mammal,
+considering the position of the pig {58} in the mammalian series, has
+likewise been attributed, perhaps truly, to reversion.[130]
+
+    When flowers which are properly irregular in structure become regular
+    or peloric, the change is generally looked at by botanists as a return
+    to the primitive state. But Dr. Maxwell Masters,[131] who has ably
+    discussed this subject, remarks that when, for instance, all the sepals
+    of a Tropaeolum become green and of the same shape, instead of being
+    coloured with one alone prolonged into a spur, or when all the petals
+    of a Linaria become simple and regular, such cases may be due merely to
+    an arrest of development; for in these flowers all the organs during
+    their earliest condition are symmetrical, and, if arrested at this
+    stage of growth, they would not become irregular. If, moreover, the
+    arrest were to take place at a still earlier period of development, the
+    result would be a simple tuft of green leaves; and no one probably
+    would call this a case of reversion. Dr. Masters designates the cases
+    first alluded to as regular peloria; and others, in which all the
+    corresponding parts assume a similar form of irregularity, as when all
+    the petals in a Linaria become spurred, as irregular peloria. We have
+    no right to attribute these latter cases to reversion, until it can be
+    shown to be probable that the parent-form, for instance, of the genus
+    Linaria had had all its petals spurred; for a change of this nature
+    might result from the spreading of an anomalous structure, in
+    accordance with the law, to be discussed in a future chapter, of
+    homologous parts tending to vary in the same manner. But as both forms
+    of peloria frequently occur on the same individual plant of the
+    Linaria,[132] they probably stand in some close relation to each other.
+    On the doctrine that peloria is simply the result of an arrest of
+    development, it is difficult to understand how an organ arrested at a
+    very early period of growth should acquire its full functional
+    perfection;--how a petal, supposed to be thus arrested, should acquire
+    its brilliant colours, and serve as an envelope to the flower, or a
+    stamen produce efficient pollen; yet this occurs with many peloric
+    flowers. That pelorism is not due to mere chance variability, but
+    either to an arrest of development or to reversion, we may infer from
+    an observation made by Ch. Morren,[133] namely, that families which
+    have irregular flowers often "return by these monstrous growths to
+    their regular form; whilst we never see a regular flower realise the
+    structure of an irregular one."
+
+    Some flowers have almost certainly become more or less completely
+    peloric through reversion. _Corydalis tuberosa_ properly has one of its
+    two nectaries colourless, destitute of nectar, only half the size of
+    the other, and {59} therefore, to a certain extent, in a rudimentary
+    state; the pistil is curved towards the perfect nectary, and the hood,
+    formed of the inner petals, slips off the pistil and stamens in one
+    direction alone, so that, when a bee sucks the perfect nectary, the
+    stigma and stamens are exposed and rubbed against the insect's body. In
+    several closely allied genera, as in Dielytra, &c., there are two
+    perfect nectaries, the pistil is straight, and the hood slips off on
+    either side, according as the bee sucks either nectary. Now, I have
+    examined several flowers of _Corydalis tuberosa_, in which both
+    nectaries were equally developed and contained nectar; in this we see
+    only the redevelopment of a partially aborted organ; but with this
+    redevelopment the pistil becomes straight, and the hood slips off in
+    either direction; so that these flowers have acquired the perfect
+    structure, so well adapted for insect agency, of Dielytra and its
+    allies. We cannot attribute these coadapted modifications to chance, or
+    to correlated variability; we must attribute them to reversion to a
+    primordial condition of the species.
+
+    The peloric flowers of Pelargonium have their five petals in all
+    respects alike, and there is no nectary; so that they resemble the
+    symmetrical flowers of the closely allied Geranium-genus; but the
+    alternate stamens are also sometimes destitute of anthers, the
+    shortened filaments being left as rudiments, and in this respect they
+    resemble the symmetrical flowers of the closely allied genus, Erodium.
+    Hence we are led to look at the peloric flowers of Pelargonium as
+    having probably reverted to the state of some primordial form, the
+    progenitor of the three closely related genera of Pelargonium,
+    Geranium, and Erodium.
+
+    In the peloric form of _Antirrhinum majus_, appropriately called the
+    "_Wonder_," the tubular and elongated flowers differ wonderfully from
+    those of the common snapdragon; the calyx and the mouth of the corolla
+    consist of six equal lobes, and include six equal instead of four
+    unequal stamens. One of the two additional stamens is manifestly formed
+    by the development of a microscopically minute papilla, which may be
+    found at the base of the upper lip of the flower in all common
+    snapdragons, at least in nineteen plants examined by me. That this
+    papilla is a rudiment of a stamen was well shown by its various degrees
+    of development in crossed plants between the common and peloric
+    Antirrhinum. Again, a peloric _Galeobdolon luteum_, growing in my
+    garden, had five equal petals, all striped like the ordinary lower lip,
+    and included five equal instead of four unequal stamens; but Mr. R.
+    Keeley, who sent me this plant, informs me that the flowers vary
+    greatly, having from four to six lobes to the corolla, and from three
+    to six stamens.[134] Now, as the members of the two great families to
+    which the Antirrhinum and Galeobdolon belong are properly pentamerous,
+    with some of the parts confluent and others suppressed, we ought not to
+    look at the sixth stamen and the sixth lobe to the corolla in either
+    case as due to reversion, any more than the additional petals in double
+    flowers in these same two families. But the case is different with the
+    fifth stamen in the peloric Antirrhinum, which {60} is produced by the
+    redevelopment of a rudiment always present, and which probably reveals
+    to us the state of the flower, as far as the stamens are concerned, at
+    some ancient epoch. It is also difficult to believe that the other four
+    stamens and the petals, after an arrest of development at a very early
+    embryonic age, would have come to full perfection in colour, structure,
+    and function, unless these organs had at some former period normally
+    passed through a similar course of growth. Hence it appears to me
+    probable that the progenitor of the genus Antirrhinum must at some
+    remote epoch have included five stamens and borne flowers in some
+    degree resembling those now produced by the peloric form.
+
+    Lastly, I may add that many instances have been recorded of flowers,
+    not generally ranked as peloric, in which certain organs, normally few
+    in number, have been abnormally augmented. As such an increase of parts
+    cannot be looked at as an arrest of development, nor as due to the
+    redevelopment of rudiments, for no rudiments are present, and as these
+    additional parts bring the plant into closer relationship with its
+    natural allies, they ought probably to be viewed as reversions to a
+    primordial condition.
+
+These several facts show us in an interesting manner how intimately certain
+abnormal states are connected together; namely, arrests of development
+causing parts to become rudimentary or to be wholly suppressed,--the
+redevelopment of parts at present in a more or less rudimentary
+condition,--the reappearance of organs of which not a vestige can now be
+detected,--and to these may be added, in the case of animals, the presence
+during youth, and subsequent disappearance, of certain characters which
+occasionally are retained throughout life. Some naturalists look at all
+such abnormal structures as a return to the ideal state of the group to
+which the affected being belongs; but it is difficult to conceive what is
+meant to be conveyed by this expression. Other naturalists maintain, with
+greater probability and distinctness of view, that the common bond of
+connection between the several foregoing cases is an actual, though
+partial, return to the structure of the ancient progenitor of the group. If
+this view be correct, we must believe that a vast number of characters,
+capable of evolution, lie hidden in every organic being. But it would be a
+mistake to suppose that the number is equally great in all beings. We know,
+for instance, that plants of many orders occasionally become peloric; but
+many more cases have been observed in the Labiatae and Scrophulariaceae
+than in any other order; and in one genus of the Scrophulariaceae, namely
+Linaria, no less {61} than thirteen species have been described in a
+peloric condition.[135] On this view of the nature of peloric flowers, and
+bearing in mind what has been said with respect to certain monstrosities in
+the animal kingdom, we must conclude that the progenitors of most plants
+and animals, though widely different in structure, have left an impression
+capable of redevelopment on the germs of their descendants.
+
+The fertilised germ of one of the higher animals, subjected as it is to so
+vast a series of changes from the germinal cell to old age,--incessantly
+agitated by what Quatrefages well calls the _tourbillon vital_,--is perhaps
+the most wonderful object in nature. It is probable that hardly a change of
+any kind affects either parent, without some mark being left on the germ.
+But on the doctrine of reversion, as given in this chapter, the germ
+becomes a far more marvellous object, for, besides the visible changes to
+which it is subjected, we must believe that it is crowded with invisible
+characters, proper to both sexes, to both the right and left side of the
+body, and to a long line of male and female ancestors separated by hundreds
+or even thousands of generations from the present time; and these
+characters, like those written on paper with invisible ink, all lie ready
+to be evolved under certain known or unknown conditions.
+
+       *       *       *       *       *
+
+
+{62}
+
+CHAPTER XIV.
+
+INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL
+LIMITATION--CORRESPONDENCE OF AGE.
+
+    FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF
+    INHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME
+    FAMILY, IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN
+    THE OTHER; SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND
+    VISIBLE IN ONE BREED AND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY
+    SEX--NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN
+    TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX
+    ALONE--INHERITANCE AT CORRESPONDING PERIODS OF LIFE--THE IMPORTANCE OF
+    THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED
+    ANIMALS; AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED
+    DISEASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN THE
+    PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS.
+
+In the two last chapters the nature and force of Inheritance, the
+circumstances which interfere with its power, and the tendency to
+Reversion, with its many remarkable contingencies, were discussed. In the
+present chapter some other related phenomena will be treated of, as fully
+as my materials permit.
+
+_Fixedness of Character._
+
+It is a general belief amongst breeders that the longer any character has
+been transmitted by a breed, the more firmly it will continue to be
+transmitted. I do not wish to dispute the truth of the proposition, that
+inheritance gains strength simply through long continuance, but I doubt
+whether it can be proved. In one sense the proposition is little better
+than a truism; if any character has remained constant during many
+generations, it will obviously be little likely, the conditions of life
+remaining the same, to vary during the next generation. So, again, in
+improving a breed, if care be taken for a length of time to exclude all
+inferior individuals, the breed will obviously tend to become truer, as it
+will not have been crossed during many generations by an inferior animal.
+We have previously seen, {63} but without being able to assign any cause,
+that, when a new character appears, it is occasionally from the first well
+fixed, or fluctuates much, or wholly fails to be transmitted. So it is with
+the aggregate of slight differences which characterise a new variety, for
+some propagate their kind from the first much truer than others. Even with
+plants multiplied by bulbs, layers, &c., which may in one sense be said to
+form parts of the same individual, it is well known that certain varieties
+retain and transmit through successive bud-generations their newly-acquired
+characters more truly than others. In none of these, nor in the following
+cases, does there appear to be any relation between the force with which a
+character is transmissible and the length of time during which it has
+already been transmitted. Some varieties, such as white and yellow
+hyacinths and white sweet-peas, transmit their colours more faithfully than
+do the varieties which have retained their natural colour. In the Irish
+family, mentioned in the twelfth chapter, the peculiar tortoiseshell-like
+colouring of the eyes was transmitted far more faithfully than any ordinary
+colour. Ancon and Mauchamp sheep and niata cattle, which are all
+comparatively modern breeds, exhibit remarkably strong powers of
+inheritance. Many similar cases could be adduced.
+
+As all domesticated animals and cultivated plants have varied, and yet are
+descended from aboriginally wild forms, which no doubt had retained the
+same character from an immensely remote epoch, we see that scarcely any
+degree of antiquity ensures a character being transmitted perfectly true.
+In this case, however, it may be said that changed conditions of life
+induce certain modifications, and not that the power of inheritance fails;
+but in every case of failure, some cause, either internal or external, must
+interfere. It will generally be found that the parts in our domesticated
+productions which have varied, or which still continue to vary,--that is,
+which fail to retain their primordial state,--are the same with the parts
+which differ in the natural species of the same genus. As, on the theory of
+descent with modification, the species of the same genus have been modified
+since they branched off from a common progenitor, it follows that the
+characters by which they differ from each other have varied whilst other
+parts of the organisation have remained unchanged; and it might be argued
+that {64} these same characters now vary under domestication, or fail to be
+inherited, owing to their lesser antiquity. But we must believe structures,
+which have already varied, would be more liable to go on varying, rather
+than structures which during an immense lapse of time have remained
+unaltered; and this variation is probably the result of certain relations
+between the conditions of life and the organisation, quite independently of
+the greater or less antiquity of each particular character.
+
+Fixedness of character, or the strength of inheritance, has often been
+judged of by the preponderance of certain characters in the crossed
+offspring between distinct races; but prepotency of transmission here comes
+into play, and this, as we shall immediately see, is a very different
+consideration from the strength or weakness of inheritance. It has often
+been observed[136] that breeds of animals inhabiting wild and mountainous
+countries cannot be permanently modified by our improved breeds; and as
+these latter are of modern origin, it has been thought that the greater
+antiquity of the wilder breeds has been the cause of their resistance to
+improvement by crossing; but it is more probably due to their structure and
+constitution being better adapted to the surrounding conditions. When
+plants are first subjected to culture, it has been found that, during
+several generations, they transmit their characters truly, that is, do not
+vary, and this has been attributed to ancient characters being strongly
+inherited; but it may with equal or greater probability be consequent on
+changed conditions of life requiring a long time for their accumulative
+action. Notwithstanding these considerations, it would perhaps be rash to
+deny that characters become more strongly fixed the longer they are
+transmitted; but I believe that the proposition resolves itself into
+this,--that all characters of all kinds, whether new or old, tend to be
+inherited, and that those which have already withstood all counteracting
+influences and been truly transmitted, will, as a general rule, continue to
+withstand them, and consequently be faithfully inherited.
+
+{65}
+
+_Prepotency in the Transmission of Character._
+
+When individuals distinct enough to be recognised, but of the same family,
+or when two well-marked races, or two species, are crossed, the usual
+result, as stated in the previous chapter, is, that the offspring in the
+first generation are intermediate between their parents, or resemble one
+parent in one part and the other parent in another part. But this is by no
+means the invariable rule; for in many cases it is found that certain
+individuals, races, and species are prepotent in transmitting their
+likeness. This subject has been ably discussed by Prosper Lucas,[137] but
+is rendered extremely complicated by the prepotency sometimes running
+equally in both sexes, and sometimes more strongly in one sex than in the
+other; it is likewise complicated by the presence of secondary sexual
+characters, which render the comparison of mongrels with their
+parent-breeds difficult.
+
+It would appear that in certain families some one ancestor, and after him
+others in the same family, must have had great power in transmitting their
+likeness through the male line; for we cannot otherwise understand how the
+same features should so often be transmitted after marriages with various
+females, as has been the case with the Austrian Emperors, and as, according
+to Niebuhr, formerly occurred in certain Roman families with their mental
+qualities.[138] The famous bull Favourite is believed[139] to have had a
+prepotent influence on the shorthorn race. It has also been observed[140]
+with English race-horses that certain mares have generally transmitted
+their own character, whilst other mares of equally pure blood have allowed
+the character of the sire to prevail.
+
+    The truth of the principle of prepotency comes out more clearly when
+    certain races are crossed. The improved Shorthorns, notwithstanding
+    that the breed is comparatively modern, are generally acknowledged to
+    possess great power in impressing their likeness on all other breeds;
+    and it is chiefly in consequence of this power that they are so highly
+    valued {66} for exportation.[141] Godine has given a curious case of a
+    ram of a goat-like breed of sheep from the Cape of Good Hope, which
+    produced offspring hardly to be distinguished from himself, when
+    crossed with ewes of twelve other breeds. But two of these half-bred
+    ewes, when put to a merino ram, produced lambs closely resembling the
+    merino breed. Girou de Buzareingues[142] found that of two races of
+    French sheep the ewes of one, when crossed during successive
+    generations with merino rams, yielded up their character far sooner
+    than the ewes of the other race. Sturm and Girou have given analogous
+    cases with other breeds of sheep and with cattle, the prepotency
+    running in these cases through the male side; but I was assured on good
+    authority in South America, that when niata cattle are crossed with
+    common cattle, though the niata breed is prepotent whether males or
+    females are used, yet that the prepotency is strongest through the
+    female line. The Manx cat is tailless and has long hind legs; Dr.
+    Wilson crossed a male Manx with common cats, and, out of twenty-three
+    kittens, seventeen were destitute of tails; but when the female Manx
+    was crossed by common male cats all the kittens had tails, though they
+    were generally short and imperfect.[143]
+
+    In making reciprocal crosses between pouter and fantail pigeons, the
+    pouter-race seemed to be prepotent through both sexes over the fantail.
+    But this is probably due to weak power in the fantail rather than to
+    any unusually strong power in the pouter, for I have observed that
+    barbs also preponderated over fantails. This weakness of transmission
+    in the fantail, though the breed is an ancient one, is said[144] to be
+    general; but I have observed one exception to the rule, namely, in a
+    cross between a fantail and laugher. The most curious instance known to
+    me of weak power in both sexes is in the trumpeter pigeon. This breed
+    has been well known for at least 130 years: it breeds perfectly true,
+    as I have been assured by those who have long kept many birds: it is
+    characterised by a peculiar tuft of feathers over the beak, by a crest
+    on the head, by a most peculiar coo quite unlike that of any other
+    breed, and by much-feathered feet. I have crossed both sexes with
+    turbits of two sub-breeds, with almond tumblers, spots, and runts, and
+    reared many mongrels and recrossed them; and though the crest on the
+    head and feathered feet were inherited (as is generally the case with
+    most breeds), I have never seen a vestige of the tuft over the beak or
+    heard the peculiar coo. Boitard and Corbie[145] assert that this is the
+    invariable result of crossing trumpeters with any other breed:
+    Neumeister,[146] however, states that in Germany mongrels have been
+    obtained, though very rarely, which were furnished with the tuft and
+    would trumpet: but a pair of these mongrels with a tuft, which I
+    imported, never trumpeted. Mr. Brent states[147] that the crossed
+    offspring of a trumpeter were crossed {67} with trumpeters for three
+    generations, by which time the mongrels had 7-8ths of this blood in
+    their veins, yet the tuft over the beak did not appear. At the fourth
+    generation the tuft appeared, but the birds, though now having 15-16ths
+    trumpeter's blood, still did not trumpet. This case well shows the wide
+    difference between inheritance and prepotency; for here we have a
+    well-established old race which transmits it characters faithfully, but
+    which, when crossed with any other race, has the feeblest power of
+    transmitting its two chief characteristic qualities.
+
+    I will give one other instance with fowls and pigeons of weakness and
+    strength in the transmission of the same character to their crossed
+    offspring. The Silk-fowl breeds true, and there is reason to believe is
+    a very ancient race; but when I reared a large number of mongrels from
+    a Silk-hen by a Spanish cock, not one exhibited even a trace of the
+    so-called silkiness. Mr. Hewitt also asserts that in no instance are
+    the silky feathers transmitted by this breed when crossed with any
+    other variety. But three birds out of many raised by Mr. Orton from a
+    cross between a silk-cock and a bantam-hen, had silky feathers.[148] So
+    that it is certain that this breed very seldom has the power of
+    transmitting its peculiar plumage to its crossed progeny. On the other
+    hand, there is a silk sub-variety of the fantail pigeon, which has its
+    feathers in nearly the same state as in the Silk-fowl: now we have
+    already seen that fantails, when crossed, possess singularly weak power
+    in transmitting their general qualities; but the silk sub-variety when
+    crossed with any other small-sized race invariably transmits its silky
+    feathers![149]
+
+    The law of prepotency comes into action when species are crossed, as
+    with races and individuals. Gaertner has unequivocally shown[150] that
+    this is the case with plants. To give one instance: when _Nicotiana
+    paniculata_ and _vincaeflora_ are crossed, the character of _N.
+    paniculata_ is almost completely lost in the hybrid; but if _N.
+    quadrivalvis_ be crossed with _N. vincaeflora_, this later species,
+    which was before so prepotent, now in its turn almost disappears under
+    the power of _N. quadrivalvis_. It is remarkable that the prepotency of
+    one species over another in transmission is quite independent, as shown
+    by Gaertner, of the greater or less facility with which the one
+    fertilises the other.
+
+    With animals, the jackal is prepotent over the dog, as is stated by
+    Flourens who made many crosses between these animals; and this was
+    likewise the case with a hybrid which I once saw between a jackal and
+    terrier. I cannot doubt, from the observations of Colin and others,
+    that the ass is prepotent over the horse; the prepotency in this
+    instance running more strongly through the male than through the female
+    ass; so that the mule resembles the ass more closely than does the
+    hinny.[151] The {68} male pheasant, judging from Mr. Hewitt's
+    descriptions,[152] and from the hybrids which I have seen,
+    preponderates over the domestic fowl; but the latter, as far as colour
+    is concerned, has considerable power of transmission, for hybrids
+    raised from five differently coloured hens differed greatly in plumage.
+    I formerly examined some curious hybrids in the Zoological Gardens,
+    between the Penguin variety of the common duck and the Egyptian goose
+    (_Tadorna Aegyptiaca_); and although I will not assert that the
+    domesticated variety preponderated over the natural species, yet it had
+    strongly impressed its unnatural upright figure on these hybrids.
+
+    I am aware that such cases as the foregoing have been ascribed by
+    various authors, not to one species, race, or individual being
+    prepotent over the other in impressing it character on its crossed
+    offspring, but to such rules as that the father influences the external
+    characters and the mother the internal or vital organs. But the great
+    diversity of the rules given by various authors almost proves their
+    falseness. Dr. Prosper Lucas has fully discussed this point, and has
+    shown[153] that none of the rules (and I could add others to those
+    quoted by him) apply to all animals. Similar rules have been enounced
+    for plants, and have been proved by Gaertner[154] to be all erroneous.
+    If we confine our view to the domesticated races of a single species,
+    or perhaps even to the species of the same genus, some such rules may
+    hold good; for instance, it seems that in reciprocally crossing various
+    breeds of fowls the male generally gives colour;[155] but conspicuous
+    exceptions have passed under my own eyes. In sheep it seems that the
+    ram usually gives its peculiar horns and fleece to its crossed
+    offspring, and the bull the presence or absence of horns.
+
+    In the following chapter on Crossing I shall have occasion to show that
+    certain characters are rarely or never blended by crossing, but are
+    {69} transmitted in an unmodified state from either parent-form; I
+    refer to this fact here because it is sometimes accompanied on the one
+    side by prepotency, which thus acquires the false appearance of unusual
+    strength. In the same chapter I shall show that the rate at which a
+    species or breed absorbs and obliterates another by repeated crosses,
+    depends in chief part on prepotency in transmission.
+
+In conclusion, some of the cases above given,--for instance, that of the
+trumpeter pigeon,--prove that there is a wide difference between mere
+inheritance and prepotency. This latter power seems to us, in our
+ignorance, to act in most cases quite capriciously. The very same
+character, even though it be an abnormal or monstrous one, such as silky
+feathers, may be transmitted by different species, when crossed, either
+with prepotent force or singular feebleness. It is obvious, that a
+purely-bred form of either sex, in all cases in which prepotency does not
+run more strongly in one sex than the other, will transmit its character
+with prepotent force over a mongrelized and already variable form.[156]
+From several of the above-given cases we may conclude that mere antiquity
+of character does not by any means necessarily make it prepotent. In some
+cases prepotency apparently depends on the same character being present and
+visible in one of the two breeds which are crossed, and latent or invisible
+in the other breed; and in this case it is natural that the character which
+is potentially present in both should be prepotent. Thus, we have reason to
+believe that there is a latent tendency in all horses to be dun-coloured
+and striped; and when a horse of this kind is crossed with one of any other
+colour, it is said that the offspring are almost sure to be striped. Sheep
+have a similar latent tendency to become dark-coloured, and we have seen
+with what prepotent force a ram with a few black spots, when crossed with
+sheep of various breeds, coloured its offspring. All pigeons have a latent
+tendency to become slaty-blue, with certain characteristic marks, and it is
+known that, when a bird thus coloured is crossed with one of any other
+colour, it is most difficult afterwards to eradicate the blue tint. A
+nearly parallel case is offered by those black bantams which, as they grow
+{70} old, develop a latent tendency to acquire red feathers. But there are
+exceptions to the rule: hornless breeds of cattle possess a latent capacity
+to reproduce horns, yet when crossed with horned breeds they do not
+invariably produce offspring bearing horns.
+
+We meet with analogous cases with plants. Striped flowers, though they can
+be propagated truly by seed, have a latent tendency to become uniformly
+coloured, but when once crossed by a uniformly coloured variety, they ever
+afterwards fail to produce striped seedlings.[157] Another case is in some
+respects more curious: plants bearing peloric or regular flowers have so
+strong a latent tendency to reproduce their normally irregular flowers,
+that this often occurs by buds when a plant is transplanted into poorer or
+richer soil.[158] Now I crossed the peloric snapdragon (_Antirrhinum
+majus_), described in the last chapter, with pollen of the common form; and
+the latter, reciprocally, with peloric pollen. I thus raised two great beds
+of seedlings, and not one was peloric. Naudin[159] obtained the same result
+from crossing a peloric Linaria with the common form. I carefully examined
+the flowers of ninety plants of the crossed Antirrhinum in the two beds,
+and their structure had not been in the least affected by the cross, except
+that in a few instances the minute rudiment of the fifth stamen, which is
+always present, was more fully or even completely developed. It must not be
+supposed that this entire obliteration of the peloric structure in the
+crossed plants can be accounted for by any incapacity of transmission; for
+I raised a large bed of plants from the peloric Antirrhinum, artificially
+fertilised by its own pollen, and sixteen plants, which alone survived the
+winter, were all as perfectly peloric as the parent-plant. Here we have a
+good instance of the wide difference between the inheritance of a character
+and the power of transmitting it to crossed offspring. The crossed plants,
+which perfectly resembled the common snapdragon, were allowed to sow
+themselves, and, out of a hundred and twenty-seven seedlings, eighty-eight
+proved to be common snapdragons, two were in an intermediate condition
+between the peloric and normal state, {71} and thirty-seven were perfectly
+peloric, having reverted to the structure of their one grandparent. This
+case seems at first sight to offer an exception to the rule formerly given,
+namely, that a character which is present in one form and latent in the
+other is generally transmitted with prepotent force when the two forms are
+crossed. For in all the Scrophulariaceae, and especially in the genera
+Antirrhinum and Linaria, there is, as was shown in the last chapter, a
+strong latent tendency to become peloric; and there is also, as we have
+just seen, a still stronger tendency in all peloric plants to reacquire
+their normal irregular structure. So that we have two opposed latent
+tendencies in the same plants. Now, with the crossed Antirrhinums the
+tendency to produce normal or irregular flowers, like those of the common
+Snapdragon, prevailed in the first generation; whilst the tendency to
+pelorism, appearing to gain strength by the intermission of a generation,
+prevailed to a large extent in the second set of seedlings. How it is
+possible for a character to gain strength by the intermission of a
+generation, will be considered in the chapter on pangenesis.
+
+On the whole, the subject of prepotency is extremely intricate,--from its
+varying so much in strength, even in regard to the same character, in
+different animals,--from its running either equally in both sexes, or, as
+frequently is the case with animals, but not with plants, much stronger in
+the one sex than the other,--from the existence of secondary sexual
+characters,--from the transmission of certain characters being limited, as
+we shall immediately see, by sex,--from certain characters not blending
+together,--and, perhaps, occasionally from the effects of a previous
+fertilisation on the mother. It is therefore not surprising that every one
+hitherto has been baffled in drawing up general rules on the subject of
+prepotency.
+
+_Inheritance as limited by Sex._
+
+New characters often appear in one sex, and are afterwards transmitted to
+the same sex, either exclusively or in a much greater degree than to the
+other. This subject is important, because with animals of many kinds in a
+state of nature, both high and low in the scale, secondary sexual
+characters, not in {72} any way directly connected with the organs of
+reproduction, are often conspicuously present. With our domesticated
+animals, also, these same secondary characters are often found to differ
+greatly from the state in which they exist in the parent-species. And the
+principle of inheritance as limited by sex shows how such characters might
+have been first acquired and subsequently modified.
+
+    Dr. P. Lucas, who has collected many facts on this subject, shows[160]
+    that when a peculiarity, in no manner connected with the reproductive
+    organs, appears in either parent, it is often transmitted exclusively
+    to the offspring of the same sex, or to a much greater number of them
+    than of the opposite sex. Thus, in the family of Lambert, the horn-like
+    projections on the skin were transmitted from the father to his sons
+    and grandsons alone; so it has been with other cases of ichthyosis,
+    with supernumerary digits, with a deficiency of digits and phalanges,
+    and in a lesser degree with various diseases, especially with
+    colour-blindness, and a haemorrhagic diathesis, that is, an extreme
+    liability to profuse and uncontrollable bleeding from trifling wounds.
+    On the other hand, mothers have transmitted, during several
+    generations, to their daughters alone, supernumerary and deficient
+    digits, colour-blindness, and other peculiarities. So that we see that
+    the very same peculiarity may become attached to either sex, and be
+    long inherited by that sex alone; but the attachment in certain cases
+    is much more frequent to one than the other sex. The same peculiarities
+    also may be promiscuously transmitted to either sex. Dr. Lucas gives
+    other cases, showing that the male occasionally transmits his
+    peculiarities to his daughters alone, and the mother to her sons alone;
+    but even in this case we see that inheritance is to a certain extent,
+    though inversely, regulated by sex. Dr. Lucas, after weighing the whole
+    evidence, comes to the conclusion that every peculiarity, according to
+    the sex in which it first appears, tends to be transmitted in a greater
+    or lesser degree to that sex.
+
+    A few details from the many cases collected by Mr. Sedgwick,[161] may
+    be here given. Colour-blindness, from some unknown cause, shows itself
+    much oftener in males than in females; in upwards of two hundred cases
+    collected by Mr. Sedgwick, nine-tenths related to men; but it is
+    eminently liable to be transmitted through women. In the case given by
+    Dr. Earle, members of eight related families were affected during five
+    generations: these families consisted of sixty-one individuals, namely,
+    of thirty-two males, of whom nine-sixteenths were incapable of
+    distinguishing colour, and of twenty-nine females, of whom only
+    one-fifteenth were thus affected. {73} Although colour-blindness thus
+    generally clings to the male sex, nevertheless, in one instance in
+    which it first appeared in a female, it was transmitted during five
+    generations to thirteen individuals, all of whom were females. A
+    haemorrhagic diathesis, often accompanied by rheumatism, has been known
+    to affect the males alone during five generations, being transmitted,
+    however, through the females. It is said that deficient phalanges in
+    the fingers have been inherited by the females alone during ten
+    generations. In another case, a man thus deficient in both hands and
+    feet, transmitted the peculiarity to his two sons and one daughter; but
+    in the third generation, out of nineteen grandchildren, twelve sons had
+    the family defect, whilst the seven daughters were free. In ordinary
+    cases of sexual limitation, the sons or daughters inherit the
+    peculiarity, whatever it may be, from their father or mother, and
+    transmit it to their children of the same sex; but generally with the
+    haemorrhagic diathesis, and often with colour-blindness, and in some
+    other cases, the sons never inherit the peculiarity directly from their
+    fathers, but the daughters, and the daughters alone, transmit the
+    latent tendency, so that the sons of the daughters alone exhibit it.
+    Thus, the father, grandson, and great-great-grandson will exhibit a
+    peculiarity,--the grandmother, daughter, and great-granddaughter having
+    transmitted it in a latent state. Hence we have, as Mr. Sedgwick
+    remarks, a double kind of atavism or reversion; each grandson
+    apparently receiving and developing the peculiarity from his
+    grandfather, and each daughter apparently receiving the latent tendency
+    from her grandmother.
+
+    From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick, and
+    others, there can be no doubt that peculiarities first appearing in
+    either sex, though not in any way necessarily or invariably connected
+    with that sex, strongly tend to be inherited by the offspring of the
+    same sex, but are often transmitted in a latent state through the
+    opposite sex.
+
+    Turning now to domesticated animals, we find that certain characters
+    not proper to the parent-species are often confined to, and inherited
+    by, one sex alone; but we do not know the history of the first
+    appearance of such characters. In the chapter on Sheep, we have seen
+    that the males of certain races differ greatly from the females in the
+    shape of their horns, these being absent in the ewes of some breeds, in
+    the development of fat in the tail in certain fat-tailed breeds, and in
+    the outline of the forehead. These differences, judging from the
+    character of the allied wild species, cannot be accounted for by
+    supposing that they have been derived from distinct parent-forms. There
+    is, also, a great difference between the horns of the two sexes in one
+    Indian breed of goats. The bull zebu is said to have a larger hump than
+    the cow. In the Scotch deer-hound the two sexes differ in size more
+    than in any other variety of the dog,[162] and, judging from analogy,
+    more than in the aboriginal parent-species. The peculiar colour called
+    tortoise-shell is very rarely seen in a male cat; the males of this
+    variety being of a rusty tint. A tendency to baldness in man before the
+    advent of old age is certainly inherited; and in the European, or at
+    least in the {74} Englishman, is an attribute of the male sex, and may
+    almost be ranked as an incipient secondary sexual character.
+
+    In various breeds of the fowl the males and females often differ
+    greatly; and these differences are far from being the same with those
+    which distinguish the two sexes in the parent-species, the _Gallus
+    bankiva_; and consequently have originated under domestication. In
+    certain sub-varieties of the Game race we have the unusual case of the
+    hens differing from each other more than the cocks. In an Indian breed
+    of a white colour stained with soot, the hens invariably have black
+    skins, and their bones are covered by a black periosteum, whilst the
+    cocks are never or most rarely thus characterised. Pigeons offer a more
+    interesting case; for the two sexes rarely differ throughout the whole
+    great family, and the males and females of the parent-form, the _C.
+    livia_, are undistinguishable; yet we have seen that with Pouters the
+    male has the characteristic quality of pouting more strongly developed
+    than the female; and in certain sub-varieties[163] the males alone are
+    spotted or striated with black. When male and female English
+    carrier-pigeons are exhibited in separate pens, the difference in the
+    development of the wattle over the beak and round the eyes is
+    conspicuous. So that here we have instances of the appearance of
+    secondary sexual characters in the domesticated races of a species in
+    which such differences are naturally quite absent.
+
+On the other hand, secondary sexual characters which properly belong to the
+species are sometimes quite lost, or greatly diminished, under
+domestication. We see this in the small size of the tusks in our improved
+breeds of the pig, in comparison with those of the wild boar. There are
+sub-breeds of fowls in which the males have lost the fine flowing
+tail-feathers and hackles; and others in which there is no difference in
+colour between the two sexes. In some cases the barred plumage, which in
+gallinaceous birds is commonly the attribute of the hen, has been
+transferred to the cock, as in the cuckoo sub-breeds. In other cases
+masculine characters have been partly transferred to the female, as with
+the splendid plumage of the golden-spangled Hamburgh hen, the enlarged comb
+of the Spanish hen, the pugnacious disposition of the Game hen, and as in
+the well-developed spurs which occasionally appear in the hens of various
+breeds. In Polish fowls both sexes are ornamented with a topknot, that of
+the male being formed of hackle-like feathers, and this is a new male
+character in the genus Gallus. On the whole, as far as I can judge, new
+characters are more apt {75} to appear in the males of our domesticated
+animals than in the females, and afterwards to be either exclusively or
+more strongly inherited by the males. Finally, in accordance with the
+principle of inheritance as limited by sex, the appearance of secondary
+sexual characters in natural species offers no especial difficulty, and
+their subsequent increase and modification, if of any service to the
+species, would follow through that form of selection which in my 'Origin of
+Species' I have called sexual selection.
+
+_Inheritance at corresponding periods of Life._
+
+This is an important subject. Since the publication of my 'Origin of
+Species,' I have seen no reason to doubt the truth of the explanation there
+given of perhaps the most remarkable of all the facts in biology, namely,
+the difference between the embryo and the adult animal. The explanation is,
+that variations do not necessarily or generally occur at a very early
+period of embryonic growth, and that such variations are inherited at a
+corresponding age. As a consequence of this the embryo, even when the
+parent-form undergoes a great amount of modification, is left only slightly
+modified; and the embryos of widely-different animals which are descended
+from a common progenitor remain in many important respects like each other
+and their common progenitor. We can thus understand why embryology should
+throw a flood of light on the natural system of classification, for this
+ought to be as far as possible genealogical. When the embryo leads an
+independent life, that is, becomes a larva, it has to be adapted to the
+surrounding conditions in its structure and instincts, independently of
+those of its parents; and the principle of inheritance at corresponding
+periods of life renders this possible.
+
+This principle is, indeed, in one way so obvious that it escapes attention.
+We possess a number of races of animals and plants, which, when compared
+with each other and with their parent-forms, present conspicuous
+differences, both in the immature and mature states. Look at the seeds of
+the several kinds of peas, beans, maize, which can be propagated truly, and
+see how they differ in size, colour, and shape, whilst the {76} full-grown
+plants differ but little. Cabbages on the other hand differ greatly in
+foliage and manner of growth, but hardly at all in their seeds; and
+generally it will be found that the differences between cultivated plants
+at different periods of growth are not necessarily closely connected
+together, for plants may differ much in their seeds and little when
+full-grown, and conversely may yield seeds hardly distinguishable, yet
+differ much when full-grown. In the several breeds of poultry, descended
+from a single species, differences in the eggs and chickens, in the plumage
+at the first and subsequent moults, in the comb and wattles during
+maturity, are all inherited. With man peculiarities in the milk and second
+teeth, of which I have received the details, are inheritable, and with man
+longevity is often transmitted. So again with our improved breeds of cattle
+and sheep, early maturity, including the early development of the teeth,
+and with certain breeds of fowl the early appearance of secondary sexual
+characters, all come under the same head of inheritance at corresponding
+periods.
+
+Numerous analogous facts could be given. The silk-moth, perhaps, offers the
+best instance; for in the breeds which transmit their characters truly, the
+eggs differ in size, colour, and shape;--the caterpillars differ, in
+moulting three or four times, in colour, even in having a dark-coloured
+mark like an eyebrow, and in the loss of certain instincts;--the cocoons
+differ in size, shape, and in the colour and quality of the silk; these
+several differences being followed by slight or barely distinguishable
+differences in the mature moth.
+
+But it may be said that, if in the above cases a new peculiarity is
+inherited, it must be at the corresponding stage of development; for an egg
+or seed can resemble only an egg or seed, and the horn in a full-grown ox
+can resemble only a horn. The following cases show inheritance at
+corresponding periods more plainly, because they refer to peculiarities
+which might have supervened, as far as we can see, earlier or later in
+life, yet are inherited at the same period at which they first appeared.
+
+    In the Lambert family the porcupine-like excrescences appeared in the
+    father and sons at the same age, namely, about nine weeks after {77}
+    birth.[164] In the extraordinary hairy family described by Mr.
+    Crawfurd,[165] children were produced during three generations with
+    hairy ears; in the father the hair began to grow over his body at six
+    years old; in his daughter somewhat earlier, namely, at one year; and
+    in both generations the milk teeth appeared late in life, the permanent
+    teeth being afterwards singularly deficient. Greyness of hair at an
+    unusually early age has been transmitted in some families. These cases
+    border on diseases inherited at corresponding periods of life, to which
+    I shall immediately refer.
+
+    It is a well-known peculiarity with almond-tumbler pigeons, that the
+    full beauty and peculiar character of the plumage does not appear until
+    the bird has moulted two or three times. Neumeister describes and
+    figures a breed of pigeons in which the whole body is white except the
+    breast, neck, and head; but before the first moult all the white
+    feathers acquire coloured edges. Another breed is more remarkable: its
+    first plumage is black, with rusty-red wing-bars and a crescent-shaped
+    mark on the breast; these marks then became white, and remain so during
+    three or four moults; but after this period the white spreads over the
+    body, and the bird loses its beauty.[166] Prize canary-birds have their
+    wings and tail black: "this colour, however, is only retained until the
+    first moult, so that they must be exhibited ere the change takes place.
+    Once moulted, the peculiarity has ceased. Of course all the birds
+    emanating from this stock have black wings and tails the first
+    year."[167] A curious and somewhat analogous account has been
+    given[168] of a family of wild pied rooks which were first observed in
+    1798, near Chalfont, and which every year from that date up to the
+    period of the published notice, viz. 1837, "have several of their brood
+    particoloured, black and white. This variegation of the plumage,
+    however, disappears with the first moult; but among the next young
+    families there are always a few pied ones." These changes of plumage,
+    which appear and are inherited at various corresponding periods of life
+    in the pigeon, canary-bird, and rook, are remarkable, because the
+    parent-species undergo no such change.
+
+    Inherited diseases afford evidence in some respects of less value than
+    the foregoing cases, because diseases are not necessarily connected
+    with any change in structure; but in other respects of more value,
+    because the periods have been more carefully observed. Certain diseases
+    are communicated to the child apparently by a process like inoculation,
+    and the child is from the first affected; such cases may be here passed
+    over. Large classes of diseases usually appear at certain ages, such as
+    St. Vitus's dance in youth, consumption in early mid-life, gout later,
+    and apoplexy still later; and these are naturally inherited at the same
+    period. But even in diseases of this class, instances have been
+    recorded, as with St. Vitus's {78} dance, showing that an unusually
+    early or late tendency to the disease is inheritable.[169] In most
+    cases the appearance of any inherited disease is largely determined by
+    certain critical periods in each person's life, as well as by
+    unfavourable conditions. There are many other diseases, which are not
+    attached to any particular period, but which certainly tend to appear
+    in the child at about the same age at which the parent was first
+    attacked. An array of high authorities, ancient and modern, could be
+    given in support of this proposition. The illustrious Hunter believed
+    in it; and Piorry[170] cautions the physician to look closely to the
+    child at the period when any grave inheritable disease attacked the
+    parent. Dr. Prosper Lucas,[171] after collecting facts from every
+    source, asserts that affections of all kinds, though not related to any
+    particular period of life, tend to reappear in the offspring at
+    whatever period of life they first appeared in the progenitor.
+
+    As the subject is important, it may be well to give a few instances,
+    simply as illustrations, not as proof; for proof, recourse must be had
+    to the authorities above quoted. Some of the following cases have been
+    selected for the sake of showing that, when a slight departure from the
+    rule occurs, the child is affected somewhat earlier in life than the
+    parent. In the family of Le Compte blindness was inherited during three
+    generations, and no less than thirty-seven children and grandchildren
+    were all affected at about the same age, namely seventeen or
+    eighteen.[172] In another case a father and his four children all
+    became blind at twenty-one years old; in another, a grandmother grew
+    blind at thirty-five, her daughter at nineteen, and three grandchildren
+    at the ages of thirteen and eleven.[173] So with deafness, two
+    brothers, their father and paternal grandfather, all became deaf at the
+    age of forty.[174]
+
+    Esquirol gives several striking instances of insanity coming on at the
+    same age, as that of a grandfather, father, and son, who all committed
+    suicide near their fiftieth year. Many other cases could be given, as
+    of a whole family who became insane at the age of forty.[175] Other
+    cerebral affections sometimes follow the same rule,--for instance,
+    epilepsy and apoplexy. A woman died of the latter disease when
+    sixty-three years old; one of her daughters at forty-three, and the
+    other at sixty-seven: the latter had twelve children, who all died from
+    tubercular meningitis.[176] I mention this latter case because it
+    illustrates a frequent occurrence, namely, a change in the precise
+    nature of an inherited disease, though still affecting the same organ.
+
+    {79}
+
+    Asthma has attacked several members of the same family when forty years
+    old, and other families during infancy. The most different diseases, as
+    angina pectoris, stone in the bladder, and various affections of the
+    skin, have appeared in successive generations at nearly the same age.
+    The little finger of a man began from some unknown cause to grow
+    inwards, and the same finger in his two sons began at the same age to
+    bend inwards in a similar manner. Strange and inexplicable neuralgic
+    affections have caused parents and children to suffer agonies at about
+    the same period of life.[177]
+
+    I will give only two other cases, which are interesting as illustrating
+    the disappearance as well as the appearance of disease at the same age.
+    Two brothers, their father, their paternal uncles, seven cousins, and
+    their paternal grandfather, were all similarly affected by a
+    skin-disease, called pityriasis versicolor; "the disease, strictly
+    limited to the males of the family (though transmitted through the
+    females), usually appeared at puberty, and disappeared at about the age
+    of forty or forty-five years." The second case is that of four
+    brothers, who when about twelve years old suffered almost every week
+    from severe headaches, which were relieved only by a recumbent position
+    in a dark room. Their father, paternal uncles, paternal grandfather,
+    and paternal granduncles all suffered in the same way from headaches,
+    which ceased at the age of fifty-four or fifty-five in all those who
+    lived so long. None of the females of the family were affected.[178]
+
+It is impossible to read the foregoing accounts, and the many others which
+have been recorded, of diseases coming on during three or even more
+generations, at the same age in several members of the same family,
+especially in the case of rare affections in which the coincidence cannot
+be attributed to chance, and doubt that there is a strong tendency to
+inheritance in disease at corresponding periods of life. When the rule
+fails, the disease is apt to come on earlier in the child than in the
+parent; the exceptions in the other direction being vey much rarer. Dr.
+Lucas[179] alludes to several cases of inherited diseases coming on at an
+earlier period. I have already given one striking instance with blindness
+during three generations; and Mr. Bowman remarks that this frequently
+occurs with cataract. With cancer there seems to be a peculiar liability to
+earlier inheritance: Mr. Paget, who has particularly {80} attended to this
+subject, and tabulated a large number of cases, informs me that he believes
+that in nine cases out of ten the later generation suffers from the disease
+at an earlier period than the previous generation. He adds, "In the
+instances in which the opposite relation holds, and the members of later
+generations have cancer at a later age than their predecessors, I think it
+will be found that the non-cancerous parents have lived to extreme old
+ages." So that the longevity of a non-affected parent seems to have the
+power of determining in the offspring the fatal period; and we thus
+apparently get another element of complexity in inheritance.
+
+The facts, showing that with certain diseases the period of inheritance
+occasionally or even frequently advances, are important with respect to the
+general descent-theory, for they render it in some degree probable that the
+same thing would occur with ordinary modifications of structure. The final
+result of a long series of such advances would be the gradual obliteration
+of characters proper to the embryo and larva, which would thus come to
+resemble more and more closely the mature parent-form. But any structure
+which was of service to the embryo or larva would be preserved by the
+destruction at this stage of growth of each individual which manifested any
+tendency to lose at too early an age its own proper character.
+
+Finally, from the numerous races of cultivated plants and domestic animals,
+in which the seed or eggs, the young or old, differ from each other and
+from their parent-species;--from the cases in which new characters have
+appeared at a particular period, and afterwards have been inherited at the
+same period;--and from what we know with respect to disease, we must
+believe in the truth of the great principle of inheritance at corresponding
+periods of life.
+
+       *       *       *       *       *
+
+_Summary of the three preceding Chapters._--Strong as is the force of
+inheritance, it allows the incessant appearance of new characters. These,
+whether beneficial or injurious, of the most trifling importance, such as a
+shade of colour in a flower, a coloured lock of hair, or a mere gesture; or
+of the highest importance, as when affecting the brain or an organ so
+perfect {81} and complex as the eye; or of so grave a nature as to deserve
+to be called a monstrosity, or so peculiar as not to occur normally in any
+member of the same natural class, are all sometimes strongly inherited by
+man, the lower animals, and plants. In numberless cases it suffices for the
+inheritance of a peculiarity that one parent alone should be thus
+characterised. Inequalities in the two sides of the body, though opposed to
+the law of symmetry, may be transmitted. There is a considerable body of
+evidence showing that even mutilations, and the effects of accidents,
+especially or perhaps exclusively when followed by disease, are
+occasionally inherited. There can be no doubt that the evil effects of
+long-continued exposure in the parent to injurious conditions are sometimes
+transmitted to the offspring. So it is, as we shall see in a future
+chapter, with the effects of the use and disuse of parts, and of mental
+habits. Periodical habits are likewise transmitted, but generally, as it
+would appear, with little force.
+
+Hence we are led to look at inheritance as the rule, and non-inheritance as
+the anomaly. But this power often appears to us in our ignorance to act
+capriciously, transmitting a character with inexplicable strength or
+feebleness. The very same peculiarity, as the weeping habit of trees,
+silky-feathers, &c., may be inherited either firmly or not at all by
+different members of the same group, and even by different individuals of
+the same species, though treated in the same manner. In this latter case we
+see that the power of transmission is a quality which is merely individual
+in its attachment. As with single characters, so it is with the several
+concurrent slight differences which distinguish sub-varieties or races; for
+of these, some can be propagated almost as truly as species, whilst others
+cannot be relied on. The same rule holds good with plants, when propagated
+by bulbs, offsets, &c., which in one sense still form parts of the same
+individual, for some varieties retain or inherit through successive
+bud-generations their character far more truly than others.
+
+Some characters not proper to the parent-species have certainly been
+inherited from an extremely remote epoch, and may therefore be considered
+as firmly fixed. But it is doubtful whether length of inheritance in itself
+gives fixedness of character; {82} though the chances are obviously in
+favour of any character which has long been transmitted true or unaltered,
+still being transmitted true as long as the conditions of life remain the
+same. We know that many species, after having retained the same character
+for countless ages, whilst living under their natural conditions, when
+domesticated have varied in the most diversified manner, that is, have
+failed to transmit their original form; so that no character appears to be
+absolutely fixed. We can sometimes account for the failure of inheritance
+by the conditions of life being opposed to the development of certain
+characters; and still oftener, as with plants cultivated by grafts and
+buds, by the conditions causing new and slight modifications incessantly to
+appear. In this latter case it is not that inheritance wholly fails, but
+that new characters are continually superadded. In some few cases, in which
+both parents are similarly characterised, inheritance seems to gain so much
+force by the combined action of the two parents, that it counteracts its
+own power, and a new modification is the result.
+
+In many cases the failure of the parents to transmit their likeness is due
+to the breed having been at some former period crossed; and the child takes
+after his grandparent or more remote ancestor of foreign blood. In other
+cases, in which the breed has not been crossed, but some ancient character
+has been lost through variation, it occasionally reappears through
+reversion, so that the parents apparently fail to transmit their own
+likeness. In all cases, however, we may safely conclude that the child
+inherits all its characters from its parents, in whom certain characters
+are latent, like the secondary sexual characters of one sex in the other.
+When, after a long succession of bud-generations, a flower or fruit becomes
+separated into distinct segments, having the colours or other attributes of
+both parent-forms, we cannot doubt that these characters were latent in the
+earlier buds, though they could not then be detected, or could be detected
+only in an intimately commingled state. So it is with animals of crossed
+parentage, which with advancing years occasionally exhibit characters
+derived from one of their two parents, of which not a trace could at first
+be perceived. Certain monstrosities, which resemble what naturalists call
+the typical form of the group in question, {83} apparently come under the
+same law of reversion. It is assuredly an astonishing fact that the male
+and female sexual elements, that buds, and even full-grown animals, should
+retain characters, during several generations in the case of crossed
+breeds, and during thousands of generations in the case of pure breeds,
+written as it were in invisible ink, yet ready at any time to be evolved
+under the requisite conditions.
+
+What these conditions are, we do not in many cases at all know. But the act
+of crossing in itself, apparently from causing some disturbance in the
+organisation, certainly gives a strong tendency to the reappearance of
+long-lost characters, both corporeal and mental, independently of those
+derived from the cross. A return of any species to its natural conditions
+of life, as with feral animals and plants, favours reversion; though it is
+certain that this tendency exists, we do not know how far it prevails, and
+it has been much exaggerated. On the other hand, the crossed offspring of
+plants which have had their organisation disturbed by cultivation, are more
+liable to reversion than the crossed offspring of species which have always
+lived under their natural conditions.
+
+When distinguishable individuals of the same family, or races, or species
+are crossed, we see that the one is often prepotent over the other in
+transmitting its own character. A race may possess a strong power of
+inheritance, and yet when crossed, as we have seen with trumpeter-pigeons,
+yield to the prepotency of every other race. Prepotentcy of transmission
+may be equal in the two sexes of the same species, but often runs more
+strongly in one sex. It plays an important part in determining the rate at
+which one race can be modified or wholly absorbed by repeated crosses with
+another. We can seldom tell what makes one race or species prepotent over
+another; but it sometimes depends on the same character being present and
+visible in one parent, and latent or potentially present in the other.
+
+Characters may first appear in either sex, but oftener in the male than in
+the female, and afterwards be transmitted to the offspring of the same sex.
+In this case we may feel confident that the peculiarity in question is
+really present though latent in the opposite sex; hence the father may
+transmit through his daughter any character to his grandson; and the mother
+{84} conversely to her granddaughter. We thus learn, and the fact is an
+important one, that transmission and development are distinct powers.
+Occasionally these two powers seem to be antagonistic, or incapable of
+combination in the same individual; for several cases have been recorded in
+which the son has not directly inherited a character from his father, or
+directly transmitted it to his son, but has received it by transmission
+through his non-affected mother, and transmitted it through his
+non-affected daughter. Owing to inheritance being limited by sex, we can
+see how secondary sexual characters may first have arisen under nature;
+their preservation and accumulation being dependent on their service to
+either sex.
+
+At whatever period of life a new character first appears, it generally
+remains latent in the offspring until a corresponding age is attained, and
+then it is developed. When this rule fails, the child generally exhibits
+the character at an earlier period than the parent. On this principle of
+inheritance at corresponding periods, we can understand how it is that most
+animals display from the germ to maturity such a marvellous succession of
+characters.
+
+Finally, though much remains obscure with respect to Inheritance, we may
+look at the following laws as fairly well established. Firstly, a tendency
+in every character, new and old, to be transmitted by seminal and bud
+generation, though often counteracted by various known and unknown causes.
+Secondly, reversion or atavism, which depends on transmission and
+development being distinct powers: it acts in various degrees and manners
+through both seminal and bud generation. Thirdly, prepotency of
+transmission, which may be confined to one sex, or be common to both sexes
+of the prepotent form. Fourthly, transmission, limited by sex, generally to
+the same sex in which the inherited character first appeared. Fifthly,
+inheritance at corresponding periods of life, with some tendency to the
+earlier development of the inherited character. In these laws of
+Inheritance, as displayed under domestication, we see an ample provision
+for the production, through variability and natural selection, of new
+specific forms.
+
+       *       *       *       *       *
+
+
+{85}
+
+CHAPTER XV.
+
+ON CROSSING.
+
+    FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED
+    BREEDS--WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE
+    ABSORBS THE OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF
+    TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL
+    ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN
+    CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE
+    SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES,
+    AND THE FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE
+    BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT
+    SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.
+
+In the two previous chapters, when discussing reversion and prepotency, I
+was necessarily led to give many facts on crossing. In the present chapter
+I shall consider the part which crossing plays in two opposed
+directions,--firstly, in obliterating characters, and consequently in
+preventing the formation of new races; and secondly, in the modification of
+old races, or in the formation of new and intermediate races, by a
+combination of characters. I shall also show that certain characters are
+incapable of fusion.
+
+The effects of free or uncontrolled breeding between the members of the
+same variety or of closely allied varieties are important; but are so
+obvious that they need not be discussed at much length. It is free
+intercrossing which chiefly gives uniformity, both under nature and under
+domestication, to the individuals of the same species or variety, when they
+live mingled together and are not exposed to any cause inducing excessive
+variability. The prevention of free crossing, and the intentional matching
+of individual animals, are the corner-stones of the breeder's art. No man
+in his senses would expect to improve or modify a breed in any particular
+manner, or keep an old breed true and distinct, unless he separated his
+animals. The killing of inferior animals in each generation comes to the
+{86} same thing as their separation. In savage and semi-civilised
+countries, where the inhabitants have not the means of separating their
+animals, more than a single breed of the same species rarely or never
+exists. In former times, even in a country so civilised as North America,
+there were no distinct races of sheep, for all had been mingled
+together.[180] The celebrated agriculturist Marshall[181] remarks that
+"sheep that are kept within fences, as well as shepherded flocks in open
+countries, have generally a similarity, if not a uniformity, of character
+in the individuals of each flock;" for they breed freely together, and are
+prevented from crossing with other kinds; whereas in the unenclosed parts
+of England the unshepherded sheep, even of the same flock, are far from
+true or uniform, owing to various breeds having mingled and crossed. We
+have seen that the half-wild cattle in the several British parks are
+uniform in character in each; but in the different parks, from not having
+mingled and crossed during many generations, they differ in a slight
+degree.
+
+We cannot doubt that the extraordinary number of varieties and
+sub-varieties of the pigeon, amounting to at least one hundred and fifty,
+is partly due to their remaining, differently from other domesticated
+birds, paired for life when once matched. On the other hand, breeds of cats
+imported into this country soon disappear, for their nocturnal and rambling
+habits render it hardly possible to prevent free crossing. Rengger[182]
+gives an interesting case with respect to the cat in Paraguay: in all the
+distant parts of the kingdom it has assumed, apparently from the effects of
+the climate, a peculiar character, but near the capital this change has
+been prevented, owing, as he asserts, to the native animal frequently
+crossing with cats imported from Europe. In all cases like the foregoing,
+the effects of an occasional cross will be augmented by the increased
+vigour and fertility of the crossed offspring, of which fact evidence will
+hereafter be given; for this will lead to the mongrels increasing more
+rapidly than the pure parent-breeds.
+
+{87}
+
+When distinct breeds are allowed to cross freely, the result will be a
+heterogenous body; for instance, the dogs in Paraguay are far from uniform,
+and can no longer be affiliated to their parent-races.[183] The character
+which a crossed body of animals will ultimately assume must depend on
+several contingencies,--namely, on the relative numbers of the individuals
+belonging to the two or more races which are allowed to mingle; on the
+prepotency of one race over the other in the transmission of character; and
+on the conditions of life to which they are exposed. When two commingled
+breeds exist at first in nearly equal numbers, the whole will sooner or
+later become intimately blended, but not so soon, both breeds being equally
+favoured in all respects, as might have been expected. The following
+calculation[184] shows that this is the case: if a colony with an equal
+number of black and white men were founded, and we assume that they marry
+indiscriminately, are equally prolific, and that one in thirty annually
+dies and is born; then "in 65 years the number of blacks, whites, and
+mulattoes would be equal. In 91 years the whites would be 1-10th, the
+blacks 1-10th, and the mulattoes, or people of intermediate degrees of
+colour, 8-10ths of the whole number. In three centuries not 1-100th part of
+the whites would exist."
+
+When one of two mingled races exceeds the other greatly in number, the
+latter will soon be wholly, or almost wholly, absorbed and lost.[185] Thus
+European pigs and dogs have been largely introduced into the islands of the
+Pacific Ocean, and the native races have been absorbed and lost in the
+course of about fifty or sixty years;[186] but the imported races no doubt
+were favoured. Rats may be considered as semi-domesticated animals. Some
+snake-rats (_Mus alexandrinus_) escaped in the Zoological Gardens of
+London, "and for a long time afterwards the keepers frequently caught
+cross-bred rats, at first half-breds, afterwards with less and less of the
+character of the snake-rat, till at length all traces of it
+disappeared."[187] On the other hand, {88} in some parts of London,
+especially near the docks, where fresh rats are frequently imported, an
+endless variety of intermediate forms may be found between the brown,
+black, and snake rat, which are all three usually ranked as distinct
+species.
+
+How many generations are necessary for one species or race to absorb
+another by repeated crosses has often been discussed;[188] and the
+requisite number has probably been much exaggerated. Some writers have
+maintained that a dozen, or score, or even more generations, are necessary;
+but this in itself is improbable, for in the tenth generation there will be
+only 1-1024th part of foreign blood in the offspring. Gaertner found,[189]
+that with plants one species could be made to absorb another in from three
+to five generations, and he believes that this could always be effected in
+from six to seventh generations. In one instance, however, Koelreuter[190]
+speaks of the offspring of _Mirabilis vulgaris_, crossed during eight
+successive generations by _M. longiflora_, as resembling this latter
+species so closely, that the most scrupulous observer could detect "vix
+aliquam notabilem differentiam;"--he succeeded, as he says, "ad plenariam
+fere transmutationem." But this expression shows that the act of absorption
+was not even then absolutely complete, though these crossed plants
+contained only the 1-256th part of _M. vulgaris_. The conclusions of such
+accurate observers as Gaertner and Koelreuter are of far higher worth than
+those made without scientific aim by breeders. The most remarkable
+statement which I have met with of the persistent endurance of the effects
+of a single cross is given by Fleischmann,[191] who, in reference to German
+sheep, says "that the original coarse sheep have 5500 fibres of wool on a
+square inch; grades of the third or fourth Merino cross produced about
+8000, the twentieth cross 27,000, the perfect pure Merino blood 40,000 to
+48,000." So that in this case common German sheep crossed twenty times
+successively with Merinos have not by any means acquired wool as fine as
+that of the pure breed. In all cases, the rate of absorption will {89}
+depend largely on the conditions of life being favourable to any particular
+character; and we may suspect that there would be under the climate of
+Germany a constant tendency to degeneration in the wool of Merinos, unless
+prevented by careful selection; and thus perhaps the foregoing remarkable
+case may be explained. The rate of absorption must also depend on the
+amount of distinguishable difference between the two forms which are
+crossed, and especially, as Gaertner insists, on prepotency of transmission
+in the one form over the other. We have seen in the last chapter that one
+of two French breeds of sheep yielded up its character, when crossed with
+Merinos, very much slower than the other; and the common German sheep
+referred to by Fleischmann may present an analogous case. But in all cases
+there will be during many subsequent generations more or less liability to
+reversion, and it is this fact which has probably led authors to maintain
+that a score or more of generations are requisite for one race to absorb
+another. In considering the final result of the commingling of two or more
+breeds, we must not forget that the act of crossing in itself tends to
+bring back long-lost characters not proper to the immediate parent-forms.
+
+With respect to the influence of the conditions of life on any two breeds
+which are allowed to cross freely, unless both are indigenous and have long
+been accustomed to the country where they live, they will, in all
+probability, be unequally affected by the conditions, and this will modify
+the result. Even with indigenous breeds, it will rarely or never occur that
+both are equally well adapted to the surrounding circumstances; more
+especially when permitted to roam freely, and not carefully tended, as will
+generally be the case with breeds allowed to cross. As a consequence of
+this, natural selection will to a certain extent come into action, and the
+best fitted will survive, and this will aid in determining the ultimate
+character of the commingled body.
+
+How long a time it would require before such a crossed body of animals
+would assume within a limited area a uniform character no one can say; that
+they would ultimately become uniform from free intercrossing, and from the
+survival of the fittest, we may feel assured; but the character thus
+acquired would rarely or never, as we may infer from the several previous
+{90} considerations, be exactly intermediate between that of the two
+parent-breeds. With respect to the very slight differences by which the
+individuals of the same sub-variety, or even of allied varieties, are
+characterised, it is obvious that free crossing would soon obliterate such
+small distinctions. The formation of new varieties, independently of
+selection, would also thus be prevented; except when the same variation
+continually recurred from the action of some strongly predisposing cause.
+Hence we may conclude that free crossing has in all cases played an
+important part in giving to all the members of the same domestic race, and
+of the same natural species, uniformity of character, though largely
+modified by natural selection and by the direct action of the surrounding
+conditions.
+
+_On the possibility of all organic beings occasionally intercrossing._--But
+it may be asked, can free crossing occur with hermaphrodite animals and
+plants? All the higher animals, and the few insects which have been
+domesticated, have separated sexes, and must inevitably unite for each
+birth. With respect to the crossing of hermaphrodites, the subject is too
+large for the present volume, and will be more properly treated in a
+succeeding work. In my 'Origin of Species,' however, I have given a short
+abstract of the reasons which induce me to believe that all organic beings
+occasionally cross, though perhaps in some cases only at long intervals of
+time.[192] I will here just recall the fact that many plants, though
+hermaphrodite in structure, are unisexual in function;--such as those
+called by C. K. Sprengel _dichogamous_, in which the pollen and stigma of
+the same flower are matured at different periods; or those called by me
+_reciprocally dimorphic_, in which the flower's own pollen is not fitted to
+fertilise its own stigma; or again, the many kinds in which curious
+mechanical contrivances exist, effectually preventing self-fertilisation.
+There are, however, many hermaphrodite plants which are not in any way
+specially constructed to favour intercrossing, but which nevertheless
+commingle almost as freely as animals with separated sexes. This is the
+case with cabbages, radishes, and onions, as I know from {91} having
+experimented on them: even the peasants of Liguria say that cabbages must
+be prevented "from falling in love" with each other. In the orange tribe,
+Gallesio[193] remarks that the amelioration of the various kinds is checked
+by their continual and almost regular crossing. So it is with numerous
+other plants.
+
+Nevertheless some cultivated plants can be named which rarely intercross,
+as the common pea, or which never intercross, as I have reason to believe
+is the case with the sweet-pea (_Lathyrus odoratus_); yet the structure of
+these flowers certainly favours an occasional cross. The varieties of the
+tomato and aubergine (_Solanum_) and pimenta (_Pimenta vulgaris?_) are
+said[194] never to cross, even when growing alongside each other. But it
+should be observed that these are all exotic plants, and we do not know how
+they would behave in their native country when visited by the proper
+insects.
+
+It must also be admitted that some few natural species appear under our
+present state of knowledge to be perpetually self-fertilised, as in the
+case of the Bee Ophrys (_O. apifera_), though adapted in its structure to
+be occasionally crossed. The _Leersia oryzoides_ produces minute enclosed
+flowers which cannot possibly be crossed, and these alone, to the exclusion
+of the ordinary flowers, have as yet been known to yield seed.[195] A few
+additional and analogous cases could be advanced. But these facts do not
+make me doubt that it is a general law of nature that the individuals of
+the same species occasionally intercross, and that some great advantage is
+derived from this act. It is well known (and I shall hereafter have to give
+instances) that some plants, both indigenous and naturalised, rarely or
+never produce flowers; or, if they flower, never produce seeds. But no one
+is thus led to doubt that it is a general law of nature that phanerogamic
+plants should produce flowers, and that these flowers should produce seed.
+When they fail, we believe that such plants would perform their proper
+functions under different conditions, or that they formerly did so and will
+do so again. On analogous grounds, I believe that the few flowers {92}
+which do not now intercross, either would do so under different conditions,
+or that they formerly fertilised each other at intervals--the means for
+effecting this being generally still retained--and they will do so again at
+some future period, unless indeed they become extinct. On this view alone,
+many points in the structure and action of the reproductive organs in
+hermaphrodite plants and animals are intelligible,--for instance, the male
+and female organs never being so completely enclosed as to render access
+from without impossible. Hence we may conclude that the most important of
+all the means for giving uniformity to the individuals of the same species,
+namely, the capacity of occasionally intercrossing, is present, or has been
+formerly present, with all organic beings.
+
+    _On certain Characters not blending._--When two breeds are crossed
+    their characters usually become intimately fused together; but some
+    characters refuse to blend, and are transmitted in an unmodified state
+    either from both parents or from one. When grey and white mice are
+    paired, the young are not piebald nor of an intermediate tint, but are
+    pure white or of the ordinary grey colour: so it is when white and
+    common collared turtle-doves are paired. In breeding Game fowls, a
+    great authority, Mr. J. Douglas, remarks, "I may here state a strange
+    fact: if you cross a black with a white game, you get birds of both
+    breeds of the clearest colour." Sir R. Heron crossed during many years
+    white, black, brown, and fawn-coloured Angora rabbits, and never once
+    got these colours mingled in the same animal, but often all four
+    colours in the same litter.[196] Additional cases could be given, but
+    this form of inheritance is very far from universal even with respect
+    to the most distinct colours. When turnspit dogs and ancon sheep, both
+    of which have dwarfed limbs, are crossed with common breeds, the
+    offspring are not intermediate in structure, but take after either
+    parent. When tailless or hornless animals are crossed with perfect
+    animals, it frequently, but by no means invariably, happens that the
+    offspring are {93} either perfectly furnished with these organs or are
+    quite destitute of them. According to Rengger, the hairless condition
+    of the Paraguay dog is either perfectly or not at all transmitted to
+    its mongrel offspring; but I have seen one partial exception in a dog
+    of this parentage which had part of its skin hairy, and part naked; the
+    parts being distinctly separated as in a piebald animal. When Dorking
+    fowls with five toes are crossed with other breeds, the chickens often
+    have five toes on one foot and four on the other. Some crossed pigs
+    raised by Sir R. Heron between the solid-hoofed and common pig had not
+    all four feet in an intermediate condition, but two feet were furnished
+    with properly divided, and two with united hoofs.
+
+    Analogous facts have been observed with plants: Major Trevor Clarke
+    crossed the little, glabrous-leaved, annual stock (_Matthiola_), with
+    pollen of a large, red-flowered, rough-leaved, biennial stock, called
+    _cocardeau_ by the French, and the result was that half the seedlings
+    had glabrous and the other half rough leaves, but none had leaves in an
+    intermediate state. That the glabrous seedlings were the product of the
+    rough-leaved variety, and not accidentally of the mother-plant's own
+    pollen, was shown by their tall and strong habit of growth.[197] In the
+    succeeding generations raised from the rough-leaved crossed seedlings,
+    some glabrous plants appeared, showing that the glabrous character,
+    though incapable of blending with and modifying the rough leaves, was
+    all the time latent in this family of plants. The numerous plants
+    formerly referred to, which I raised from reciprocal crosses between
+    the peloric and common Antirrhinum, offer a nearly parallel case; for
+    in the first generation all the plants resembled the common form, and
+    in the next generation, out of one hundred and thirty-seven plants, two
+    alone were in an intermediate condition, the others perfectly
+    resembling either the peloric or common form. Major Trevor Clarke also
+    fertilised the above-mentioned red-flowered stock with pollen from the
+    purple Queen stock, and about half the seedlings scarcely differed in
+    habit, and not at all in the red colour of the flower, from the
+    mother-plant, the other half bearing blossoms of a rich purple, closely
+    like those of the paternal plant. Gaertner crossed many white and
+    yellow-flowered species and varieties of Verbascum; and these colours
+    were never blended, but the offspring bore either pure white or pure
+    yellow blossoms; the former in the larger proportion.[198] Dr. Herbert
+    raised many seedlings, as he informed me, from Swedish turnips crossed
+    by two other varieties, and these never produced flowers of an
+    intermediate tint, but always like one of their parents. I fertilised
+    the purple sweet-pea (_Lathyrus odoratus_), which has a dark
+    reddish-purple standard-petal and violet-coloured wings and keel, with
+    pollen of the painted-lady sweet-pea, which has a pale cherry-coloured
+    standard, and almost white wings and keel; and from the same pod I
+    twice raised plants perfectly resembling both sorts; the greater number
+    resembling the father. So perfect was the resemblance, that I should
+    have thought there had {94} been some mistake, if the plants which were
+    at first identical with the paternal variety, namely, the painted-lady,
+    had not later in the season produced, as mentioned in a former chapter,
+    flowers blotched and streaked with dark purple. I raised grandchildren
+    and great-grandchildren from these crossed plants, and they continued
+    to resemble the painted-lady, but during the later generations became
+    rather more blotched with purple, yet none reverted completely to the
+    original mother-plant, the purple sweet-pea. The following case is
+    slightly different, but still shows the same principle: Naudin[199]
+    raised numerous hybrids between the yellow _Linaria vulgaris_ and the
+    purple _L. purpurea_, and during three successive generations the
+    colours kept distinct in different parts of the same flower.
+
+    From such cases as the foregoing, in which the offspring of the first
+    generation perfectly resemble either parent, we come by a small step to
+    those cases in which differently coloured flowers borne on the same
+    root resemble both parents, and by another step to those in which the
+    same flower or fruit is striped or blotched with the two parental
+    colours, or bears a single stripe of the colour or other characteristic
+    quality of one of the parent-forms. With hybrids and mongrels it
+    frequently or even generally happens that one part of the body
+    resembles more or less closely one parent and another part the other
+    parent; and here again some resistance to fusion, or, what comes to the
+    same thing, some mutual affinity between the organic atoms of the same
+    nature, apparently comes into play, for otherwise all parts of the body
+    would be equally intermediate in character. So again, when the
+    offspring of hybrids or mongrels, which are themselves nearly
+    intermediate in character, revert either wholly or by segments to their
+    ancestors, the principle of the affinity of similar, or the repulsion
+    of dissimilar atoms, must come into action. To this principle, which
+    seems to be extremely general, we shall recur in the chapter on
+    pangenesis.
+
+    It is remarkable, as has been strongly insisted upon by Isidore
+    Geoffroy St. Hilaire in regard to animals, that the transmission of
+    characters without fusion occurs most rarely when species are crossed;
+    I know of one exception alone, namely, with the hybrids naturally
+    produced between the common and hooded crow (_Corvus corone_ and
+    _cornix_), which, however, are closely allied species, differing in
+    nothing except colour. Nor have I met with any well-ascertained cases
+    of transmission of this kind, even when one form is strongly prepotent
+    over another, when two races are crossed which have been slowly formed
+    by man's selection, and therefore resemble to a certain extent natural
+    species. Such cases as puppies in the same litter closely resembling
+    two distinct breeds, are probably due to super-foetation,--that is, to
+    the influence of two fathers. All the characters above enumerated,
+    which are transmitted in a perfect state to some of the offspring and
+    not to others,--such as distinct colours, nakedness of skin, smoothness
+    of leaves, absence of horns or tail, additional toes, pelorism, dwarfed
+    structure, &c.,--have all been known to appear suddenly in individual
+    animals and plants. From this fact, and from the several slight,
+    aggregated differences which distinguish domestic races and species
+    from {95} each other, not being liable to this peculiar form of
+    transmission, we may conclude that it is in some way connected with the
+    sudden appearance of the characters in question.
+
+_On the Modification of old Races and the Formation of new Races by
+Crossing._--We have hitherto chiefly considered the effects of crossing in
+giving uniformity of character; we must now look to an opposite result.
+There can be no doubt that crossing, with the aid of rigorous selection
+during several generations, has been a potent means in modifying old races,
+and in forming new ones. Lord Orford crossed his famous stud of greyhounds
+once with the bulldog, which breed was chosen from being deficient in
+scenting powers, and from having what was wanted, courage and perseverance.
+In the course of six or seven generations all traces of the external form
+of the bulldog were eliminated, but courage and perseverance remained.
+Certain pointers have been crossed, as I hear from the Rev. W. D. Fox, with
+the foxhound, to give them dash and speed. Certain strains of Dorking fowls
+have had a slight infusion of Game blood; and I have known a great fancier
+who on a single occasion crossed his turbit-pigeons with barbs, for the
+sake of gaining greater breadth of beak.
+
+In the foregoing cases breeds have been crossed once, for the sake of
+modifying some particular character; but with most of the improved races of
+the pig, which now breed true, there have been repeated crosses,--for
+instance, the improved Essex owes its excellence to repeated crosses with
+the Neapolitan, together probably with some infusion of Chinese blood.[200]
+So with our British sheep: almost all the races, except the Southdown, have
+been largely crossed; "this, in fact, has been the history of our principal
+breeds."[201] To give an example, the "Oxfordshire Downs" now rank as an
+established breed.[202] They were produced about the year 1830 by crossing
+"Hampshire and in some instances Southdown ewes with Cotswold rams:" now
+the Hampshire ram was itself produced by repeated crosses between the
+native {96} Hampshire sheep and Southdowns; and the long-woolled Cotswold
+were improved by crosses with the Leicester, which latter again is believed
+to have been a cross between several long-woolled sheep. Mr. Spooner, after
+considering the various cases which have been carefully recorded, concludes
+"that from a judicious pairing of cross-bred animals it is practicable to
+establish a new breed." On the Continent the history of several crossed
+races of cattle and of other animals has been well ascertained. To give one
+instance: the King of Wurtemberg, after twenty-five years' careful
+breeding, that is after six or seven generations, made a new breed of
+cattle from a cross between a Dutch and Swiss breed, combined with other
+breeds.[203] The Sebright bantam, which breeds as true as any other kind of
+fowl, was formed about sixty years ago by a complicated cross.[204] Dark
+Brahmas, which are believed by some fanciers to constitute a distinct
+species, were undoubtedly formed[205] in the United States, within a recent
+period, by a cross between Chittagongs and Cochins. With plants I believe
+there is little doubt that some kinds of turnips, now extensively
+cultivated, are crossed races; and the history of a variety of wheat which
+was raised from two very distinct varieties, and which after six years'
+culture presented an even sample, has been recorded on good authority.[206]
+
+Until quite lately, cautious and experienced breeders, though not averse to
+a single infusion of foreign blood, were almost universally convinced that
+the attempt to establish a new race, intermediate between two widely
+distinct races, was hopeless: "they clung with superstitious tenacity to
+the doctrine of purity of blood, believing it to be the ark in which alone
+true safety could be found."[207] Nor was this conviction unreasonable:
+when two distinct races are crossed, the offspring of the first generation
+are generally nearly uniform in character; but even this sometimes fails to
+be the case, especially with crossed dogs and fowls, the young of which
+from the first are sometimes much {97} diversified. As cross-bred animals
+are generally of large size and vigorous, they have been raised in great
+numbers for immediate consumption. But for breeding they are found to be
+utterly useless; for though they may be themselves uniform in character,
+when paired together they yield during many generations offspring
+astonishingly diversified. The breeder is driven to despair, and concludes
+that he will never form an intermediate race. But from the cases already
+given, and from others which have been recorded, it appears that patience
+alone is necessary; as Mr. Spooner remarks, "nature opposes no barrier to
+successful admixture; in the course of time, by the aid of selection and
+careful weeding, it is practicable to establish a new breed." After six or
+seven generations the hoped-for result will in most cases be obtained; but
+even then an occasional reversion, or failure to keep true, may be
+expected. The attempt, however, will assuredly fail if the conditions of
+life be decidedly unfavourable to the characters of either
+parent-breed.[208]
+
+Although the grandchildren and succeeding generations of cross-bred animals
+are generally variable in an extreme degree, some curious exceptions to the
+rule have been observed, both with crossed races and species. Thus Boitard
+and Corbie[209] assert that from a Pouter and a Runt "a Cavalier will
+appear, which we have classed amongst pigeons of pure race, because it
+transmits all its qualities to its posterity." The editor of the 'Poultry
+Chronicle'[210] bred some bluish fowls from a black Spanish cock and a
+Malay hen; and these remained true to colour "generation after generation."
+The Himalayan breed of rabbits was certainly formed by crossing two
+sub-varieties of the silver-grey rabbit; although it suddenly assumed its
+present character, which differs much from that of either parent-breed, yet
+it has ever since been easily and truly propagated. I crossed some Labrador
+and Penguin ducks, and recrossed the mongrels with Penguins; afterwards,
+most of the ducks reared during three generations were nearly uniform in
+character, being brown with a white crescentic mark on the lower part of
+the breast, {98} and with some white spots at the base of the beak; so that
+by the aid of a little selection a new breed might easily have been formed.
+In regard to crossed varieties of plants, Mr. Beaton remarks[211] that
+"Melville's extraordinary cross between the Scotch kale and an early
+cabbage is as true and genuine as any on record;" but in this case no doubt
+selection was practised. Gaertner[212] has given five cases of hybrids, in
+which the progeny kept constant; and hybrids between _Dianthus armeria_ and
+_deltoides_ remained true and uniform to the tenth generation. Dr. Herbert
+likewise showed me a hybrid from two species of Loasa which from its first
+production had kept constant during several generations.
+
+We have seen in the earlier chapters, that some of our domesticated
+animals, such as dogs, cattle, pigs, &c., are almost certainly descended
+from more than one species, or wild race, if any one prefers to apply this
+latter term to forms which were enabled to keep distinct in a state of
+nature. Hence the crossing of aboriginally distinct species probably came
+into play at an early period in the formation of our present races. From
+Ruetimeyer's observations there can be little doubt that this occurred with
+cattle; but in most cases some one of the forms which were allowed to cross
+freely, will, it is probable, have absorbed and obliterated the others. For
+it is not likely that semi-civilized men would have taken the necessary
+pains to modify by selection their commingled, crossed, and fluctuating
+stock. Nevertheless, those animals which were best adapted to their
+conditions of life would have survived through natural selection; and by
+this means crossing will often have indirectly aided in the formation of
+primeval domesticated breeds.
+
+Within recent times, as far as animals are concerned, the crossing of
+distinct species has done little or nothing in the formation or
+modification of our races. It is not yet known whether the species of
+silk-moth which have been recently crossed in France will yield permanent
+races. In the fourth chapter I alluded with some hesitation to the
+statement that a new breed, between the hare and rabbit, called leporides,
+had been formed in France, and was found capable of propagating {99}
+itself; but it is now positively affirmed[213] that this is an error. With
+plants which can be multiplied by buds and cuttings, hybridisation has done
+wonders, as with many kinds of Roses, Rhododendrons, Pelargoniums,
+Calceolarias, and Petunias. Nearly all these plants can be propagated by
+seed; most of them freely; but extremely few or none come true by seed.
+
+Some authors believe that crossing is the chief cause of variability,--that
+is, of the appearance of absolutely new characters. Some have gone so far
+as to look at it as the sole cause; but this conclusion is disproved by
+some of the facts given in the chapter on Bud-variation. The belief that
+characters not present in either parent or in their ancestors frequently
+originate from crossing is doubtful; that they occasionally thus arise is
+probable; but this subject will be more conveniently discussed in a future
+chapter on the causes of Variability.
+
+A condensed summary of this and of the three following chapters, together
+with some remarks on Hybridism, will be given in the nineteenth chapter.
+
+       *       *       *       *       *
+
+
+{100}
+
+CHAPTER XVI.
+
+CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OF
+DOMESTICATION ON FERTILITY.
+
+    DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN
+    CROSSED--VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF
+    BREEDING AND SEXUAL PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE
+    WHEN CROSSED--VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS,
+    AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY STERILE--DOMESTICATION
+    ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN
+    CROSSED--ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS
+    FROM DOMESTICATION AND CULTIVATION.
+
+The domesticated races of both animals and plants, when crossed, are with
+extremely few exceptions quite prolific,--in some cases even more so than
+the purely bred parent-races. The offspring, also, raised from such crosses
+are likewise, as we shall see in the following chapter, generally more
+vigorous and fertile than their parents. On the other hand, species when
+crossed, and their hybrid offspring, are almost invariability in some
+degree sterile; and here there seems to exist a broad and insuperable
+distinction between races and species. The importance of this subject as
+bearing on the origin of species is obvious; and we shall hereafter recur
+to it.
+
+It is unfortunate how few precise observations have been made on the
+fertility of mongrel animals and plants during several successive
+generations. Dr. Broca[214] has remarked that no one has observed whether,
+for instance, mongrel dogs, bred _inter se_, are indefinitely fertile; yet,
+if a shade of infertility be detected by careful observation in the
+offspring of natural forms when crossed, it is thought that their specific
+distinction is proved. But so many breeds of sheep, cattle, pigs, dogs, and
+poultry, have been crossed and recrossed in various ways, that any
+sterility, if it had existed, would from being injurious {101} almost
+certainly have been observed. In investigating the fertility of crossed
+varieties many sources of doubt occur. Whenever the least trace of
+sterility between two plants, however closely allied, was observed by
+Koelreuter, and more especially by Gaertner, who counted the exact number
+of seed in each capsule, the two forms were at once ranked as distinct
+species; and if this rule be followed, assuredly it will never be proved
+that varieties when crossed are in any degree sterile. We have formerly
+seen that certain breeds of dogs do not readily pair together; but no
+observations have been made whether, when paired, they produce the full
+number of young, and whether the latter are perfectly fertile _inter se_;
+but, supposing that some degree of sterility were found to exist,
+naturalists would simply infer that these breeds were descended from
+aboriginally distinct species; and it would be scarcely possible to
+ascertain whether or not this explanation was the true one.
+
+The Sebright Bantam is much less prolific than any other breed of fowls,
+and is descended from a cross between two very distinct breeds, recrossed
+by a third sub-variety. But it would be extremely rash to infer that the
+loss of fertility was in any manner connected with its crossed origin, for
+it may with more probability be attributed either to long-continued close
+interbreeding, or to an innate tendency to sterility correlated with the
+absence of hackles and sickle tail-feathers.
+
+Before giving the few recorded cases of forms, which must be ranked as
+varieties, being in some degree sterile when crossed, I may remark that
+other causes sometimes interfere with varieties freely intercrossing. Thus
+they may differ too greatly in size, as with some kinds of dogs and fowls:
+for instance, the editor of the 'Journal of Horticulture, &c.,'[215] says
+that he can keep Bantams with the larger breeds without much danger of
+their crossing, but not with the smaller breeds, such as Games, Hamburgs,
+&c. With plants a difference in the period of flowering serves to keep
+varieties distinct, as with the various kinds of maize and wheat: thus
+Colonel Le Couteur[216] remarks, "the Talavera wheat, from flowering much
+earlier than any other kind, is sure to continue pure." In different parts
+of {102} the Falkland Islands the cattle are breaking up into herds of
+different colours; and those on the higher ground, which are generally
+white, usually breed, as I am informed by Admiral Sulivan, three months
+earlier than those on the lowlands; and this would manifestly tend to keep
+the herds from blending.
+
+Certain domestic races seem to prefer breeding with their own kind; and
+this is a fact of some importance, for it is a step towards that
+instinctive feeling which helps to keep closely allied species in a state
+of nature distinct. We have now abundant evidence that, if it were not for
+this feeling, many more hybrids would be naturally produced than is the
+case. We have seen in the first chapter that the alco dog of Mexico
+dislikes dogs of other breeds; and the hairless dog of Paraguay mixes less
+readily with the European races, than the latter do with each other. In
+Germany the female Spitz-dog is said to receive the fox more readily than
+will other dogs; a female Australian Dingo in England attracted the wild
+male foxes. But these differences in the sexual instinct and attractive
+power of the various breeds may be wholly due to their descent from
+distinct species. In Paraguay the horses have much freedom, and an
+excellent observer[217] believes that the native horses of the same colour
+and size prefer associating with each other, and that the horses which have
+been imported from Entre Rios and Banda Oriental into Paraguay likewise
+prefer associating together. In Circassia six sub-races of the horse are
+known and have received distinct names; and a native proprietor of
+rank[218] asserts that horses of three of these races, whilst living a free
+life, almost always refuse to mingle and cross, and will even attack each
+other.
+
+It has been observed, in a district stocked with heavy Lincolnshire and
+light Norfolk sheep, that both kinds, though bred together, when turned
+out, "in a short time separate to a sheep;" the Lincolnshires drawing off
+to the rich soil, and the Norfolks to their own dry light soil; and as long
+as there is plenty of grass, "the two breeds keep themselves as distinct as
+rooks and pigeons." In this case different habits of {103} life tend to
+keep the races distinct. On one of the Faroe islands, not more than half a
+mile in diameter, the half-wild native black sheep are said not to have
+readily mixed with the imported white sheep. It is a more curious fact that
+the semi-monstrous ancon sheep of modern origin "have been observed to keep
+together, separating themselves from the rest of the flock, when put into
+enclosures with other sheep."[219] With respect to fallow deer, which live
+in a semi-domesticated condition, Mr. Bennett[220] states that the dark and
+pale coloured herds, which have long been kept together in the Forest of
+Dean, in High Meadow Woods, and in the New Forest, have never been known to
+mingle: the dark-coloured deer, it may be added, are believed to have been
+first brought by James I. from Norway, on account of their greater
+hardiness. I imported from the island of Porto Santo two of the feral
+rabbits, which differ, as described in the fourth chapter, from common
+rabbits; both proved to be males, and, though they lived during some years
+in the Zoological Gardens, the superintendent, Mr. Bartlett, in vain
+endeavoured to make them breed with various tame kinds; but whether this
+refusal to breed was due to any change in instinct, or simply to their
+extreme wildness; or whether confinement had rendered them sterile, as
+often occurs, cannot be told.
+
+Whilst matching for the sake of experiment many of the most distinct breeds
+of pigeons, it frequently appeared to me that the birds, though faithful to
+their marriage vow, retained some desire after their own kind. Accordingly
+I asked Mr. Wicking, who has kept a larger stock of various breeds together
+than any man in England, whether he thought that they would prefer pairing
+with their own kind, supposing that there were males and females enough of
+each; and he without hesitation answered that he was convinced that this
+was the case. It has often been noticed that the dovecot pigeon seems to
+have an actual aversion towards the several fancy breeds;[221] yet all have
+{104} certainly sprung from a common progenitor. The Rev. W. D. Fox informs
+me that his flocks of white and common Chinese geese kept distinct.
+
+These facts and statements, though some of them are incapable of proof,
+resting only on the opinion of experienced observers, show that some
+domestic races are led by different habits of life to keep to a certain
+extent separate, and that others prefer coupling with their own kind, in
+the same manner as species in a state of nature, though in a much less
+degree.
+
+    With respect to sterility from the crossing of domestic races, I know
+    of no well-ascertained case with animals. This fact, seeing the great
+    difference in structure between some breeds of pigeons, fowls, pigs,
+    dogs, &c., is extraordinary, in contrast with the sterility of many
+    closely allied natural species when crossed; but we shall hereafter
+    attempt to show that it is not so extraordinary as it at first appears.
+    And it may be well here to recall to mind that the amount of external
+    difference between two species will not safely guide us in foretelling
+    whether or not they will breed together,--some closely allied species
+    when crossed being utterly sterile, and others which are extremely
+    unlike being moderately fertile. I have said that no case of sterility
+    in crossed races rests on satisfactory evidence; but here is one which
+    at first seems trustworthy. Mr. Youatt,[222] and a better authority
+    cannot be quoted, states, that formerly in Lancashire crosses were
+    frequently made between longhorn and shorthorn cattle; the first cross
+    was excellent, but the produce was uncertain; in the third or fourth
+    generation the cows were bad milkers; "in addition to which, there was
+    much uncertainty whether the cows would conceive; and full one-third of
+    the cows among some of these half-breds failed to be in calf." This at
+    first seems a good case; but Mr. Wilkinson states,[223] that a breed
+    derived from this same cross was actually established in another part
+    of England; and if it had failed in fertility, the fact would surely
+    have been noticed. Moreover, supposing that Mr. Youatt had proved his
+    case, it might be argued that the sterility was wholly due to the two
+    parent-breeds being descended from primordially distinct species.
+
+    I will give a case with plants, to show how difficult it is to get
+    sufficient evidence. Mr. Sheriff, who has been so successful in the
+    formation of new races of wheat, fertilised the Hopetoun with the
+    Talavera; in the first and second generations the produce was
+    intermediate in character, but in the fourth generation "it was found
+    to consist of many varieties; nine-tenths of the florets proved barren,
+    and many of the seeds seemed shrivelled abortions, void of vitality,
+    and the whole race was evidently verging to extinction."[224] Now,
+    considering how little these {105} varieties of wheat differ in any
+    important character, it seems to me very improbable that the sterility
+    resulted, as Mr. Sheriff thought, from the cross, but from some quite
+    distinct cause. Until such experiments are many times repeated, it
+    would be rash to trust them; but unfortunately they have been rarely
+    tried even once with sufficient care.
+
+    Gaertner has recorded a more remarkable and trustworthy case: he
+    fertilised thirteen panicles (and subsequently nine others) on a dwarf
+    maize bearing yellow seed[225] with pollen of a tall maize having red
+    seed; and one head alone produced good seed, only five in number.
+    Though these plants are monoecious, and therefore do not require
+    castration, yet I should have suspected some accident in the
+    manipulation had not Gaertner expressly stated that he had during many
+    years grown these two varieties together, and they did not
+    spontaneously cross; and this, considering that the plants are
+    monoecious and abound with pollen, and are well known generally to
+    cross freely, seems explicable only on the belief that these two
+    varieties are in some degree mutually infertile. The hybrid plants
+    raised from the above five seed were intermediate in structure,
+    extremely variable, and perfectly fertile.[226] No one, I believe, has
+    hitherto suspected that these varieties of maize are distinct species;
+    but had the hybrids been in the least sterile, no doubt Gaertner would
+    at once have so classed them. I may here remark, that with undoubted
+    species there is not necessarily any close relation between the
+    sterility of a first cross and that of the hybrid offspring. Some
+    species can be crossed with facility, but produce utterly sterile
+    hybrids; others can be crossed with extreme difficulty, but the hybrids
+    when produced are moderately fertile. I am not aware, however, of any
+    instance quite like this of the maize with natural species, namely, of
+    a first cross made with difficulty, but yielding perfectly fertile
+    hybrids.
+
+    The following case is much more remarkable, and evidently perplexed
+    Gaertner, whose strong wish it was to draw a broad line of distinction
+    between species and varieties. In the genus Verbascum, he made, during
+    eighteen years, a vast number of experiments, and crossed no less than
+    1085 flowers and counted their seeds. Many of these experiments
+    consisted in crossing white and yellow varieties of both _V. lychnitis_
+    and _V. blattaria_ with nine other species and their hybrids. That the
+    white and yellow flowered plants of these two species are really
+    varieties, no one has doubted; and Gaertner actually raised in the case
+    of both species one variety from the seed of the other. Now in two of
+    his works[227] he distinctly asserts that crosses between
+    similarly-coloured flowers yield more seed than between
+    dissimilarly-coloured; so that the yellow-flowered variety of either
+    species (and conversely with the white-flowered variety), when crossed
+    with pollen of its own kind, yields more seed than when crossed with
+    that of the white variety; and so it is when differently coloured
+    species are crossed. The general results may be seen in the Table at
+    the {106} end of his volume. In one instance he gives[228] the
+    following details; but I must premise that Gaertner, to avoid
+    exaggerating the degree of sterility in his crosses, always compares
+    the _maximum_ number obtained from a cross with the _average_ number
+    naturally given by the pure mother-plant. The white-variety of _V.
+    lychnitis_, naturally fertilised by its own pollen, gave from an
+    _average_ of twelve capsules ninety-six good seeds in each; whilst
+    twenty flowers fertilised with pollen from the yellow variety of this
+    same species, gave as the _maximum_ only eighty-nine good seed; so that
+    we have the proportion of 1000 to 908, according to Gaertner's usual
+    scale. I should have thought it possible that so small a difference in
+    fertility might have been accounted for by the evil effects of the
+    necessary castration; but Gaertner shows that the white variety of _V.
+    lychnitis_, when fertilised first by the white variety of _V.
+    blattaria_, and then by the yellow variety of this species, yielded
+    seed in the proportion of 622 to 438; and in both these cases
+    castration was performed. Now the sterility which results from the
+    crossing of the differently coloured varieties of the same species, is
+    fully as great as that which occurs in many cases when distinct species
+    are crossed. Unfortunately Gaertner compared the results of the first
+    unions alone, and not the sterility of the two sets of hybrids produced
+    from the white variety of _V. lychnitis_ when fertilised by the white
+    and yellow varieties of _V. blattaria_, for it is probable that they
+    would have differed in this respect.
+
+    Mr. J. Scott has given me the results of a series of experiments on
+    Verbascum, made by him in the Botanic Gardens of Edinburgh. He repeated
+    some of Gaertner's experiments on distinct species, but obtained only
+    fluctuating results; some confirmatory, but the greater number
+    contradictory; nevertheless these seem hardly sufficient to overthrow
+    the conclusions arrived at by Gaertner from experiments tried on a much
+    larger scale. In the second place Mr. Scott experimented on the
+    relative fertility of unions between similarly and
+    dissimilarly-coloured varieties of the same species. Thus he fertilised
+    six flowers of the yellow variety of _V. lychnitis_ by its own pollen,
+    and obtained six capsules, and calling, for the sake of having a
+    standard of comparison, the average number of good seed in each one
+    hundred, he found that this same yellow variety, when fertilised by the
+    white variety, yielded from seven capsules an average of ninety-four
+    seed. On the same principle, the white variety of _V. lychnitis_ by its
+    own pollen (from six capsules), and by the pollen of the yellow variety
+    (eight capsules), yielded seed in the proportion of 100 to 82. The
+    yellow variety of _V. thapsus_ by its own pollen (eight capsules), and
+    by that of the white variety (only two capsules), yielded seed in the
+    proportion of 100 to 94. Lastly, the white variety of _V. blattaria_ by
+    its own pollen (eight capsules), and by that of the yellow variety
+    (five capsules), yielded seed in the proportion of 100 to 79. So that
+    in every case the unions of dissimilarly-coloured varieties of the same
+    species were less fertile than the unions of similarly-coloured
+    varieties; when all the cases are grouped together, the difference of
+    fertility is as 86 to 100. Some additional trials were made, and
+    altogether thirty-six similarly-coloured unions yielded thirty-five
+    good {107} capsules; whilst thirty-five dissimilarly-coloured unions
+    yielded only twenty-six good capsules. Besides the foregoing
+    experiments, the purple _V. phoeniceum_ was crossed by a rose-coloured
+    and a white variety of the same species; these two varieties were also
+    crossed together, and these several unions yielded less seed than _V.
+    phoeniceum_ by its own pollen. Hence it follows from Mr. Scott's
+    experiments, that in the genus Verbascum the similarly and
+    dissimilarly-coloured varieties of the same species behave, when
+    crossed, like closely allied but distinct species.[229]
+
+    This remarkable fact of the sexual affinity of similarly-coloured
+    varieties, as observed by Gaertner and Mr. Scott, may not be of very
+    rare occurrence; for the subject has not been attended to by others.
+    The following case is worth giving, partly to show how difficult it is
+    to avoid error. Dr. Herbert[230] has remarked that variously-coloured
+    double varieties of the hollyhock (_Althaea rosea_) may be raised with
+    certainty by seed from plants growing close together. I have been
+    informed that nurserymen who raise seed for sale do not separate their
+    plants; accordingly I procured seed of eighteen named varieties; of
+    these, eleven varieties produced sixty-two plants all perfectly true to
+    their kind; and seven produced forty-nine plants, half of which were
+    true and half false. Mr. Masters of Canterbury has given me a more
+    striking case; he saved seed from a great bed of twenty-four named
+    varieties planted in closely adjoining rows, and each variety
+    reproduced itself truly with only sometimes a shade of difference in
+    tint. Now in the hollyhock the pollen, which is abundant, is matured
+    and nearly all shed before the stigma of the same flower is ready to
+    receive it;[231] and as bees covered with pollen incessantly fly from
+    plant to plant, it would appear that adjoining varieties could not
+    escape being crossed. As, however, this does not occur, it appeared to
+    me probable that the pollen {108} of each variety was prepotent on its
+    own stigma over that of all other varieties. But Mr. C. Turner of
+    Slough, well known for his success in the cultivation of this plant,
+    informs me that it is the doubleness of the flowers which prevents the
+    bees gaining access to the pollen and stigma; and he finds that it is
+    difficult even to cross them artificially. Whether this explanation
+    will fully account for varieties in close proximity propagating
+    themselves so truly by seed, I do not know.
+
+    The following cases are worth giving, as they relate to monoecious
+    forms, which do not require, and consequently have not been injured by,
+    castration. Girou de Buzareingues crossed what he designates three
+    varieties of gourd,[232] and asserts that their mutual fertilisation is
+    less easy in proportion to the difference which they present. I am
+    aware how imperfectly the forms in this group were until recently
+    known; but Sageret,[233] who ranked them according to their mutual
+    fertility, considers the three forms above alluded to as varieties, as
+    does a far higher authority, namely, M. Naudin.[234] Sageret[235] has
+    observed that certain melons have a greater tendency, whatever the
+    cause may be, to keep true than others; and M. Naudin, who has had such
+    immense experience in this group, informs me that he believes that
+    certain varieties intercross more readily than others of the same
+    species; but he has not proved the truth of this conclusion; the
+    frequent abortion of the pollen near Paris being one great difficulty.
+    Nevertheless, he has grown close together, during seven years, certain
+    forms of Citrullus, which, as they could be artificially crossed with
+    perfect facility and produced fertile offspring, are ranked as
+    varieties; but these forms when not artificially crossed kept true.
+    Many other varieties, on the other hand, in the same group cross with
+    such facility, as M. Naudin repeatedly insists, that without being
+    grown far apart they cannot be kept in the least true.
+
+    Another case, though somewhat different, may be here given, as it is
+    highly remarkable, and is established on excellent evidence. Koelreuter
+    minutely describes five varieties of the common tobacco,[236] which
+    were reciprocally crossed, and the offspring were intermediate in
+    character and as fertile as their parents: from this fact Koelreuter
+    inferred that they are really varieties; and no one, as far as I can
+    discover, seems to have doubted that such is the case. He also crossed
+    reciprocally these five varieties with _N. glutinosa_, and they yielded
+    very sterile hybrids; but those raised from the _var. perennis_,
+    whether used as the father or mother plant, were not so sterile as the
+    hybrids from the four other varieties.[237] So that the sexual {109}
+    capacity of this one variety has certainly been in some degree
+    modified, so as to approach in nature that of _N. glutinosa_.[238]
+
+These facts with respect to plants show that in some few cases certain
+varieties have had their sexual powers so far modified, that they cross
+together less readily and yield less seed than other varieties of the same
+species. We shall presently see that the sexual functions of most animals
+and plants are eminently liable to be affected by the conditions of life to
+which they are exposed; and hereafter we shall briefly discuss the conjoint
+bearing of this and other facts on the difference in fertility between
+crossed varieties and crossed species.
+
+_Domestication eliminates the tendency to Sterility which is general with
+Species when crossed._
+
+This hypothesis was first propounded by Pallas,[239] and has been adopted
+by several authors. I can find hardly any direct facts in its support; but
+unfortunately no one has compared, in the case of either animals or plants,
+the fertility of anciently domesticated varieties, when crossed with a
+distinct species, with that of the wild parent-species when similarly
+crossed. No one has compared, for instance, the fertility of _Gallus
+bankiva_ and of the domesticated fowl, when crossed with a distinct species
+of Gallus or Phasianus; and the {110} experiment would in all cases be
+surrounded by many difficulties. Dureau de la Malle, who has so closely
+studied classical literature, states[240] that in the time of the Romans
+the common mule was produced with more difficulty than at the present day;
+but whether this statement may be trusted I know not. A much more
+important, though somewhat different, case is given by M. Groenland,[241]
+namely, that plants, known from their intermediate character and sterility
+to be hybrids between Aegilops and wheat, have perpetuated themselves under
+culture since 1857, _with a rapid but varying increase of fertility in each
+generation_. In the fourth generation the plants, still retaining their
+intermediate character, had become as fertile as common cultivated wheat.
+
+The indirect evidence in favour of the Pallasian doctrine appears to me to
+be extremely strong. In the earlier chapters I have attempted to show that
+our various breeds of dogs are descended from several wild species; and
+this probably is the case with sheep. There can no longer be any doubt that
+the Zebu or humped Indian ox belongs to a distinct species from European
+cattle: the latter, moreover, are descended from two or three forms, which
+may be called either species or wild races, but which co-existed in a state
+of nature and kept distinct. We have good evidence that our domesticated
+pigs belong to at least two specific types, _S. scrofa_ and _Indica_, which
+probably lived together in a wild state in South-eastern Europe. Now, a
+widely-extended analogy leads to the belief that if these several allied
+species, in the wild state or when first reclaimed, had been crossed, they
+would have exhibited, both in their first unions and in their hybrid
+offspring, some degree of sterility. Nevertheless the several domesticated
+races descended from them are now all, as far as can be ascertained,
+perfectly fertile together. If this reasoning be trustworthy, and it is
+apparently sound, we must admit the Pallasian doctrine that long-continued
+domestication tends to eliminate that sterility which is natural to species
+when crossed in their aboriginal state.
+
+{111}
+
+_On increased Fertility from Domestication and Cultivation._
+
+Increased fertility from domestication, without any reference to crossing,
+may be here briefly considered. This subject bears indirectly on two or
+three points connected with the modification of organic beings. As Buffon
+long ago remarked,[242] domestic animals breed oftener in the year and
+produce more young at a birth than wild animals of the same species; they,
+also, sometimes breed at an earlier age. The case would hardly have
+deserved further notice, had not some authors lately attempted to show that
+fertility increases and decreases in an inverse ratio with the amount of
+food. This strange doctrine has apparently arisen from individual animals
+when supplied with an inordinate quantity of food, and from plants of many
+kinds when grown on excessively rich soil, as on a dunghill, becoming
+sterile; but to this latter point I shall have occasion presently to
+return. With hardly an exception, our domesticated animals, which have long
+been habituated to a regular and copious supply of food, without the labour
+of searching for it, are more fertile than the corresponding wild animals.
+It is notorious how frequently cats and dogs breed, and how many young they
+produce at a birth. The wild rabbit is said generally to breed four times
+yearly, and to produce from four to eight young; the tame rabbit breeds six
+or seven times yearly, and produces from four to eleven young. The ferret,
+though generally so closely confined, is more prolific than its supposed
+wild prototype. The wild sow is remarkably prolific, for she often breeds
+twice in the year, and produces from four to eight and sometimes even
+twelve young at a birth; but the domestic sow regularly breeds twice a
+year, and would breed oftener if permitted; and a sow that produces less
+than eight at a birth "is worth little, and the sooner she is fattened for
+the butcher the better." The amount of food affects the fertility even of
+the same individual: thus sheep, which on mountains never produce more than
+one lamb at a birth, when brought {112} down to lowland pastures frequently
+bear twins. This difference apparently is not due to the cold of the higher
+land, for sheep and other domestic animals are said to be extremely
+prolific in Lapland. Hard living, also, retards the period at which animals
+conceive; for it has been found disadvantageous in the northern islands of
+Scotland to allow cows to bear calves before they are four years old.[243]
+
+    Birds offer still better evidence of increased fertility from
+    domestication: the hen of the wild _Gallus bankiva_ lays from six to
+    ten eggs, a number which would be thought nothing of with the domestic
+    hen. The wild duck lays from five to ten eggs; the tame one in the
+    course of the year from eighty to one hundred. The wild grey-lag goose
+    lays from five to eight eggs; the tame from thirteen to eighteen, and
+    she lays a second time; as Mr. Dixon has remarked, "high-feeding, care,
+    and moderate warmth induce a habit of prolificacy which becomes in some
+    measure hereditary." Whether the semi-domesticated dovecot pigeon is
+    more fertile than the wild rock-pigeon _C. livia_, I know not; but the
+    more thoroughly domesticated breeds are nearly twice as fertile as
+    dovecots: the latter, however, when caged and highly fed, become
+    equally fertile with house pigeons. The peahen alone of domesticated
+    birds is rather more fertile, according to some accounts, when wild in
+    its native Indian home, than when domesticated in Europe and exposed to
+    our much colder climate.[244]
+
+    With respect to plants, no one would expect wheat to tiller more, and
+    each ear to produce more grain, in poor than in rich soil; or to get in
+    poor soil a heavy crop of peas or beans. Seeds vary so much in number
+    {113} that it is difficult to estimate them; but on comparing beds of
+    carrots saved for seed in a nursery garden with wild plants, the former
+    seemed to produce about twice as much seed. Cultivated cabbages yielded
+    thrice as many pods by measure as wild cabbages from the rocks of South
+    Wales. The excess of berries produced by the cultivated Asparagus in
+    comparison with the wild plant is enormous. No doubt many highly
+    cultivated plants, such as pears, pineapples, bananas, sugar-cane, &c.,
+    are nearly or quite sterile; and I am inclined to attribute this
+    sterility to excess of food and to other unnatural conditions; but to
+    this subject I shall presently recur.
+
+In some cases, as with the pig, rabbit, &c., and with those plants which
+are valued for their seed, the direct selection of the more fertile
+individuals has probably much increased their fertility; and in all cases
+this may have occurred indirectly, from the better chance of the more
+numerous offspring produced by the more fertile individuals having
+survived. But with cats, ferrets, and dogs, and with plants like carrots,
+cabbages, and asparagus, which are not valued for their prolificacy,
+selection can have played only a subordinate part; and their increased
+fertility must be attributed to the more favourable conditions of life
+under which they have long existed.
+
+       *       *       *       *       *
+
+
+{114}
+
+CHAPTER XVII.
+
+ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
+INTERBREEDING.
+
+    DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID
+    TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING,
+    AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY
+    INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME
+    PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS
+    ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS,
+    GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS,
+    FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED
+    SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON
+    CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT,
+    BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH
+    DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION.
+
+The gain in constitutional vigour, derived from an occasional cross between
+individuals of the same variety, but belonging to distinct families, or
+between distinct varieties, has not been so largely or so frequently
+discussed, as have the evil effects of too close interbreeding. But the
+former point is the more important of the two, inasmuch as the evidence is
+more decisive. The evil results from close interbreeding are difficult to
+detect, for they accumulate slowly, and differ much in degree with
+different species; whilst the good effects which almost invariably follow a
+cross are from the first manifest. It should, however, be clearly
+understood that the advantage of close interbreeding, as far as the
+retention of character is concerned, is indisputable, and often outweighs
+the evil of a slight loss of constitutional vigour. In relation to the
+subject of domestication, the whole question is of some importance, as too
+close interbreeding interferes with the improvement of old races, and
+especially with the formation of new ones. It is important as indirectly
+bearing on Hybridism; and perhaps on the extinction of species, when any
+form has become so rare that only a few individuals {115} remain within a
+confined area. It bears in an important manner on the influence of free
+intercrossing, in obliterating individual differences, and thus giving
+uniformity of character to the individuals of the same race or species; for
+if additional vigour and fertility be thus gained, the crossed offspring
+will multiply and prevail, and the ultimate result will be far greater than
+otherwise would have occurred. Lastly, the question is of high interest, as
+bearing on mankind. Hence I shall discuss this subject at full length. As
+the facts which prove the evil effects of close interbreeding are more
+copious, though less decisive, than those on the good effects of crossing,
+I shall, under each group of beings, begin with the former.
+
+There is no difficulty in defining what is meant by a cross; but this is by
+no means easy in regard to "breeding in and in" or "too close
+interbreeding," because, as we shall see, different species of animals are
+differently affected by the same degree of interbreeding. The pairing of a
+father and daughter, or mother and son, or brothers and sisters, if carried
+on during several generations, is the closest possible form of
+interbreeding. But some good judges, for instance Sir J. Sebright, believe
+that the pairing of a brother and sister is closer than that of parents and
+children; for when the father is matched with his daughter he crosses, as
+is said, with only half his own blood. The consequences of close
+interbreeding carried on for too long a time, are, as is generally
+believed, loss of size, constitutional vigour, and fertility, sometimes
+accompanied by a tendency to malformation. Manifest evil does not usually
+follow from pairing the nearest relations for two, three, or even four
+generations; but several causes interfere with our detecting the evil--such
+as the deterioration being very gradual, and the difficulty of
+distinguishing between such direct evil and the inevitable augmentation of
+any morbid tendencies which may be latent or apparent in the related
+parents. On the other hand, the benefit from a cross, even when there has
+not been any very close interbreeding, is almost invariably at once
+conspicuous. There is reason to believe, and this was the opinion of that
+most experienced observer Sir J. Sebright,[245] that the evil effects of
+close interbreeding may be checked by the related individuals {116} being
+separated during a few generations and exposed to different conditions of
+life.
+
+That evil directly follows from any degree of close interbreeding has been
+denied by many persons; but rarely by any practical breeder; and never, as
+far as I know, by one who has largely bred animals which propagate their
+kind quickly. Many physiologists attribute the evil exclusively to the
+combination and consequent increase of morbid tendencies common to both
+parents: that this is an active source of mischief there can be no doubt.
+It is unfortunately too notorious that men and various domestic animals
+endowed with a wretched constitution, and with a strong hereditary
+disposition to disease, if not actually ill, are fully capable of
+procreating their kind. Close interbreeding, on the other hand, induces
+sterility; and this indicates something quite distinct from the
+augmentation of morbid tendencies common to both parents. The evidence
+immediately to be given convinces me that it is a great law of nature, that
+all organic beings profit from an occasional cross with individuals not
+closely related to them in blood; and that, on the other hand,
+long-continued close interbreeding is injurious.
+
+Various general considerations have had much influence in leading me to
+this conclusion; but the reader will probably rely more on special facts
+and opinions. The authority of experienced observers, even when they do not
+advance the grounds of their belief, is of some little value. Now almost
+all men who have bred many kinds of animals and have written on the
+subject, such as Sir J. Sebright, Andrew Knight, &c.,[246] have expressed
+the strongest conviction on the impossibility of long-continued close
+interbreeding. Those who have compiled works on agriculture, and have
+associated much with breeders, such as the sagacious Youatt, Low, &c., have
+strongly declared their opinion to the same effect. Prosper Lucas, trusting
+largely to French authorities, has come to a similar conclusion. The
+distinguished German agriculturist Hermann von Nathusius, who has written
+the most able treatise on this subject which I have met with, concurs; and
+as I shall have to quote from {117} this treatise, I may state that
+Nathusius is not only intimately acquainted with works on agriculture in
+all languages, and knows the pedigrees of our British breeds better than
+most Englishmen, but has imported many of our improved animals, and is
+himself an experienced breeder.
+
+Evidence of the evil effects of close interbreeding can most readily be
+acquired in the case of animals, such as fowls, pigeons, &c., which
+propagate quickly, and, from being kept in the same place, are exposed to
+the same conditions. Now I have inquired of very many breeders of these
+birds, and I have hitherto not met with a single man who was not thoroughly
+convinced that an occasional cross with another strain of the same
+sub-variety was absolutely necessary. Most breeders of highly-improved or
+fancy birds value their own strain, and are most unwilling, at the risk, in
+their opinion, of deterioration, to make a cross. The purchase of a
+first-rate bird of another strain is expensive, and exchanges are
+troublesome; yet all breeders, as far as I can hear, excepting those who
+keep large stocks at different places for the sake of crossing, are driven
+after a time to take this step.
+
+Another general consideration which has had great influence on my mind is,
+that with all hermaphrodite animals and plants, which it might have been
+thought would have perpetually fertilised themselves, and thus have been
+subjected for long ages to the closest interbreeding, there is no single
+species, as far as I can discover, in which the structure ensures
+self-fertilisation. On the contrary, there are in a multitude of cases, as
+briefly stated in the fifteenth chapter, manifest adaptations which favour
+or inevitably lead to an occasional cross between one hermaphrodite and
+another of the same species; and these adaptive structures are utterly
+purposeless, as far as we can see, for any other end.
+
+    With _Cattle_ there can be no doubt that extremely close interbreeding
+    may be long carried on, advantageously with respect to external
+    characters and with no manifestly apparent evil as far as constitution
+    is concerned. The same remark is applicable to sheep. Whether these
+    animals have gradually been rendered less susceptible than others to
+    this evil, in order to permit them to live in herds,--a habit which
+    leads the old and vigorous males to expel all intruders, and in
+    consequence often to pair with their own daughters, I will not pretend
+    to decide. The case of Bakewell's Long-horns, which were closely
+    interbred for a long period, has often been {118} quoted; yet Youatt
+    says[247] the breed "had acquired a delicacy of constitution
+    inconsistent with common management," and "the propagation of the
+    species was not always certain." But the Shorthorns offer the most
+    striking case of close interbreeding; for instance, the famous bull
+    Favourite (who was himself the offspring of a half-brother and sister
+    from Foljambe) was matched with his own daughter, granddaughter, and
+    great-granddaughter; so that the produce of this last union, or the
+    great-great-granddaughter, had 15-16ths, or 93.75 per cent. of the
+    blood of Favourite in her veins. This cow was matched with the bull
+    Wellington, having 62.5 per cent. of Favourite blood in his veins, and
+    produced Clarissa; Clarissa was matched with the bull Lancaster, having
+    68.75 of the same blood, and she yielded valuable offspring.[248]
+    Nevertheless Collings, who reared these animals, and was a strong
+    advocate for close breeding, once crossed his stock with a Galloway,
+    and the cows from this cross realised the highest prices. Bates's herd
+    was esteemed the most celebrated in the world. For thirteen years he
+    bred most closely in and in; but during the next seventeen years,
+    though he had the most exalted notion of the value of his own stock, he
+    thrice infused fresh blood into his herd: it is said that he did this,
+    not to improve the form of his animals, but on account of their
+    lessened fertility. Mr. Bates's own view, as given by a celebrated
+    breeder,[249] was, that "to breed in and in from a bad stock was ruin
+    and devastation; yet that the practice may be safely followed within
+    certain limits when the parents so related are descended from
+    first-rate animals." We thus see that there has been extremely close
+    interbreeding with Shorthorns; but Nathusius, after the most careful
+    study of their pedigrees, says that he can find no instance of a
+    breeder who has strictly followed this practice during his whole life.
+    From this study and his own experience, he concludes that close
+    interbreeding is necessary to ennoble the stock; but that in effecting
+    this the greatest care is necessary, on account of the tendency to
+    infertility and weakness. It may be added, that another high
+    authority[250] asserts that many more calves are born cripples from
+    Shorthorns than from other and less closely interbred races of cattle.
+
+    Although by carefully selecting the best animals (as Nature effectually
+    does by the law of battle) close interbreeding may be long carried on
+    with cattle, yet the good effects of a cross between almost any two
+    breeds is at once shown by the greater size and vigour of the
+    offspring; as Mr. Spooner writes to me, "crossing distinct breeds
+    certainly improves cattle for the butcher." Such crossed animals are of
+    course of no value to the breeder; but they have been raised during
+    many years in several {119} parts of England to be slaughtered;[251]
+    and their merit is now so fully recognised, that at fat-cattle shows a
+    separate class has been formed for their reception. The best fat ox at
+    the great show at Islington in 1862 was a crossed animal.
+
+    The half-wild cattle, which have been kept in British parks probably
+    for 400 or 500 years, or even for a longer period, have been advanced
+    by Culley and others as a case of long-continued interbreeding within
+    the limits of the same herd without any consequent injury. With respect
+    to the cattle at Chillingham, the late Lord Tankerville owned that they
+    were bad breeders.[252] The agent, Mr. Hardy, estimates (in a letter to
+    me, dated May, 1861) that in the herd of about fifty the average number
+    annually slaughtered, killed by fighting, and dying, is about ten, or
+    one in five. As the herd is kept up to nearly the same average number,
+    the annual rate of increase must be likewise about one in five. The
+    bulls, I may add, engage in furious battles, of which battles the
+    present Lord Tankerville has given me a graphic description, so that
+    there will always be rigorous selection of the most vigorous males. I
+    procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton,
+    the following account of the wild cattle kept in the Duke's park in
+    Lanarkshire, which is about 200 acres in extent. The number of cattle
+    varies from sixty-five to eighty; and the number annually killed (I
+    presume by all causes) is from eight to ten; so that the annual rate of
+    increase can hardly be more than one in six. Now in South America,
+    where the herds are half-wild, and therefore offer a nearly fair
+    standard of comparison, according to Azara the natural increase of the
+    cattle on an estancia is from one-third to one-fourth of the total
+    number, or one in between three and four; and this, no doubt, applies
+    exclusively to adult animals fit for consumption. Hence the half-wild
+    British cattle which have long interbred within the limits of the same
+    herd are relatively far less fertile. Although in an unenclosed country
+    like Paraguay there must be some crossing between the different herds,
+    yet even there the inhabitants believe that the occasional introduction
+    of animals from distant localities is necessary to prevent
+    "degeneration in size and diminution of fertility."[253] The decrease
+    in size from ancient times in the Chillingham and Hamilton cattle must
+    have been prodigious, for Professor Ruetimeyer has shown that they are
+    almost certainly the descendants of the gigantic _Bos primigenius_. No
+    doubt this decrease in size may be largely attributed to less
+    favourable conditions of life; yet animals roaming over large parks,
+    and fed during severe winters, can hardly be considered as placed under
+    very unfavourable conditions.
+
+    With _Sheep_ there has often been long-continued interbreeding within
+    the limits of the same flock; but whether the nearest relations have
+    been matched so frequently as in the case of Shorthorn cattle, I do not
+    know. The Messrs. Brown during fifty years have never infused fresh
+    blood into their excellent flock of Leicesters. Since 1810 Mr. Barford
+    has acted on the same principle with the Foscote flock. He asserts that
+    half a century {120} of experience has convinced him that when two
+    nearly related animals are quite sound in constitution, in-and-in
+    breeding does not induce degeneracy; but he adds that he "does not
+    pride himself on breeding from the nearest affinities." In France the
+    Naz flock has been bred for sixty years without the introduction of a
+    single strange ram.[254] Nevertheless, most great breeders of sheep
+    have protested against close interbreeding prolonged for too great a
+    length of time.[255] The most celebrated of recent breeders, Jonas
+    Webb, kept five separate families to work on, thus "retaining the
+    requisite distance of relationship between the sexes."[256]
+
+    Although by the aid of careful selection the near interbreeding of
+    sheep may be long continued without any manifest evil, yet it has often
+    been the practice with farmers to cross distinct breeds to obtain
+    animals for the butcher, which plainly shows that good is derived from
+    this practice. Mr. Spooner sums up his excellent Essay on Crossing by
+    asserting that there is a direct pecuniary advantage in judicious
+    cross-breeding, especially when the male is larger than the female. A
+    former celebrated breeder, Lord Somerville, distinctly states that his
+    half-breeds from Ryelands and Spanish sheep were larger animals than
+    either the pure Ryelands or pure Spanish sheep.[257]
+
+    As some of our British parks are ancient, it occurred to me that there
+    must have been long-continued close interbreeding with the fallow deer
+    (_Cervus dama_) kept in them; but on inquiry I find that it is a common
+    practice to infuse new blood by procuring bucks from other parks. Mr.
+    Shirley,[258] who has carefully studied the management of deer, admits
+    that in some parks there has been no admixture of foreign blood from a
+    time beyond the memory of man. But he concludes "that in the end the
+    constant breeding in-and-in is sure to tell to the disadvantage of the
+    whole herd, though it may take a very long time to prove it; moreover,
+    when we find, as is very constantly the case, that the introduction of
+    fresh blood has been of the very greatest use to deer, both by
+    improving their size and appearance, and particularly by being of
+    service in removing the taint of 'rickback,' if not of other diseases,
+    to which deer are sometimes subject when the blood has not been
+    changed, there can, I think, be no doubt but that a judicious cross
+    with a good stock is of the greatest consequence, and is indeed
+    essential, sooner or later, to the prosperity of every well-ordered
+    park."
+
+    Mr. Meynell's famous foxhounds have been adduced, as showing that no
+    ill effects follow from close interbreeding; and Sir J. Sebright
+    ascertained from him that he frequently bred from father and daughter,
+    mother and {121} son, and sometimes even from brothers and sisters. Sir
+    J. Sebright, however, declares,[259] that by breeding _in-and-in_, by
+    which he means matching brothers and sisters, he has actually seen
+    strong spaniels become weak and diminutive lapdogs. The Rev. W. D. Fox
+    has communicated to me the case of a small lot of bloodhounds, long
+    kept in the same family, which had become very bad breeders, and nearly
+    all had a bony enlargement in the tail. A single cross with a distinct
+    strain of bloodhounds restored their fertility, and drove away the
+    tendency to malformation in the tail. I have heard the particulars of
+    another case with bloodhounds, in which the female had to be held to
+    the male. Considering how rapid is the natural increase of the dog, it
+    is difficult to understand the high price of most highly improved
+    breeds, which almost implies long-continued close interbreeding, except
+    on the belief that this process lessens fertility and increases
+    liability to distemper and other diseases. A high authority, Mr.
+    Scrope, attributes the rarity and deterioration in size of the Scotch
+    deerhound (the few individuals now existing throughout the country
+    being all related) in large part to close interbreeding.
+
+    With all highly-bred animals there is more or less difficulty in
+    getting them to procreate quickly, and all suffer much from delicacy of
+    constitution; but I do not pretend that these effects ought to be
+    wholly attributed to close interbreeding. A great judge of rabbits[260]
+    says, "the long-eared does are often too highly bred or forced in their
+    youth to be of much value as breeders, often turning out barren or bad
+    mothers." Again: "Very long-eared bucks will also sometimes prove
+    barren." These highly-bred rabbits often desert their young, so that it
+    is necessary to have nurse-rabbits.
+
+    With _Pigs_ there is more unanimity amongst breeders on the evil
+    effects of close interbreeding than, perhaps, with any other large
+    animal. Mr. Druce, a great and successful breeder of the Improved
+    Oxfordshires (a crossed race), writes, "without a change of boars of a
+    different tribe, but of the same breed, constitution cannot be
+    preserved." Mr. Fisher Hobbs, the raiser of the celebrated Improved
+    Essex breed, divided his stock into three separate families, by which
+    means he maintained the breed for more than twenty years, "by judicious
+    selection from the _three distinct families_."[261] Lord Western was
+    the first importer of a Neapolitan boar and sow. "From this pair he
+    bred in-and-in, until the breed was in danger of becoming extinct, a
+    sure result (as Mr. Sidney remarks) of in-and-in breeding." Lord
+    Western then crossed his Neapolitan pigs with the old Essex, and made
+    the first great step towards the Improved Essex breed. Here is a more
+    interesting case. Mr. J. Wright, well known as a breeder, crossed[262]
+    the same boar with the daughter, granddaughter, and
+    great-granddaughter, and so on for seven generations. The result was,
+    that in many instances the offspring failed to breed; in others they
+    produced few that lived; and of the latter many were idiotic, without
+    sense {122} even to suck, and when attempting to move could not walk
+    straight. Now it deserves especial notice, that the two last sows
+    produced by this long course of interbreeding were sent to other boars,
+    and they bore several litters of healthy pigs. The best sow in external
+    appearance produced during the whole seven generations was one in the
+    last stage of descent; but the litter consisted of this one sow. She
+    would not breed to her sire, yet bred at the first trial to a stranger
+    in blood. So that, in Mr. Wright's case, long-continued and extremely
+    close interbreeding did not affect the external form or merit of the
+    young; but with many of them the general constitution and mental
+    powers, and especially the reproductive functions, were seriously
+    affected.
+
+    Nathusius gives[263] an analogous and even more striking case: he
+    imported from England a pregnant sow of the large Yorkshire breed, and
+    bred the product closely in-and-in for three generations: the result
+    was unfavourable, as the young were weak in constitution, with impaired
+    fertility. One of the latest sows, which he esteemed a good animal,
+    produced, when paired with her own uncle (who was known to be
+    productive with sows of other breeds), a litter of six, and a second
+    time a litter of only five weak young pigs. He then paired this sow
+    with a boar of a small black breed, which he had likewise imported from
+    England, and which boar, when matched with sows of his own breed,
+    produced from seven to nine young: now, the sow of the large breed,
+    which was so unproductive when paired with her own uncle, yielded to
+    the small black boar, in the first litter twenty-one, and in the second
+    litter eighteen young pigs; so that in one year she produced
+    thirty-nine fine young animals!
+
+    As in the case of several other animals already mentioned, even when no
+    injury is perceptible from moderately close interbreeding, yet, to
+    quote the words of Mr. Coate, a most successful breeder (who five times
+    won the annual gold medal of the Smithfield Club Show for the best pen
+    of pigs), "Crosses answer well for profit to the farmer, as you get
+    more constitution and quicker growth; but for me, who sell a great
+    number of pigs for breeding purposes, I find it will not do, as it
+    requires many years to get anything like purity of blood again."[264]
+
+Before passing on to Birds, I ought to refer to man, though I am unwilling
+to enter on this subject, as it is surrounded by natural prejudices. It has
+moreover been discussed by various authors under many points of view.[265]
+Mr. Tylor[266] has shown {123} that with widely different races, in the
+most distant quarters of the world, marriages between relations--even
+between distant relations--have been strictly prohibited. A few exceptional
+cases can be specified, especially with royal families; and these have been
+enlarged on in a learned article[267] by Mr. W. Adam, and formerly in 1828
+by Hofacker. Mr. Tylor is inclined to believe that the almost universal
+prohibition of closely-related marriages has arisen from their evil effects
+having been observed, and he ingeniously explains some apparent anomalies
+in the prohibition not extending equally to the relations on both the male
+and female side. He admits, however, that other causes, such as the
+extension of friendly alliances, may have come into play. Mr. W. Adam, on
+the other hand, concludes that related marriages are prohibited and viewed
+with repugnance from the confusion which would thus arise in the descent of
+property, and from other still more recondite reasons; but I cannot accept
+this view, seeing that the savages of Australia and South America,[268] who
+have no property to bequeath or fine moral feelings to confuse, hold the
+crime of incest in abhorrence.
+
+It would be interesting to know, if it could be ascertained, as throwing
+light on this question with respect to man, what occurs with the higher
+anthropomorphous apes--whether the young males and females soon wander away
+from their parents, or whether the old males become jealous of their sons
+and expel them, or whether any inherited instinctive feeling, from being
+beneficial, has been generated, leading the young males and females of the
+same family to prefer pairing with distinct families, and to dislike
+pairing with each other. A considerable body of evidence has already been
+advanced, showing that the offspring from parents which are not related are
+more vigorous and fertile than those from parents which are closely
+related; hence any slight feeling, arising from the sexual excitement of
+novelty or other cause, which led to the former rather than to the latter
+unions, would be augmented through natural selection, and thus might become
+instinctive; for those individuals which had an innate preference of this
+kind would increase in number. It seems more probable, that degraded
+savages should {124} thus unconsciously have acquired their dislike and
+even abhorrence of incestuous marriages, rather than that they should have
+discovered by reasoning and observation the evil results. The abhorrence
+occasionally failing is no valid argument against the feeling being
+instinctive, for any instinct may occasionally fail or become vitiated, as
+sometimes occurs with parental love and the social sympathies. In the case
+of man, the question whether evil follows from close interbreeding will
+probably never be answered by direct evidence, as he propagates his kind so
+slowly and cannot be subjected to experiment; but the almost universal
+practice of all races at all times of avoiding closely-related marriages is
+an argument of considerable weight; and whatever conclusion we arrive at in
+regard to the higher animals may be safely extended to man.
+
+    Turning now to Birds: in the case of the _Fowl_ a whole array of
+    authorities could be given against too close interbreeding. Sir J.
+    Sebright positively asserts that he made many trials, and that his
+    fowls, when thus treated, became long in the legs, small in the body,
+    and bad breeders.[269] He produced the famous Sebright Bantams by
+    complicated crosses, and by breeding in-and-in; and since his time
+    there has been much close interbreeding with these Bantams; and they
+    are now notoriously bad breeders. I have seen Silver Bantams, directly
+    descended from his stock, which had become almost as barren as hybrids;
+    for not a single chicken had been that year hatched from two full nests
+    of eggs. Mr. Hewitt says that with these Bantams the sterility of the
+    male stands, with rare exceptions, in the closest relation with their
+    loss of certain secondary male characters: he adds, "I have noticed, as
+    a general rule, that even the slightest deviation from feminine
+    character in the tail of the male Sebright--say the elongation by only
+    half an inch of the two principal tail-feathers--brings with it
+    improved probability of increased fertility."[270]
+
+    Mr. Wright states[271] that Mr. Clark, "whose fighting-cocks were so
+    notorious, continued to breed from his own kind till they lost their
+    disposition to fight, but stood to be cut up without making any
+    resistance, and were so reduced in size as to be under those weights
+    required for the best prizes; but on obtaining a cross from Mr.
+    Leighton, they again resumed their former courage and weight." It
+    should be borne in mind that game-cocks before they fought were always
+    weighed, so that nothing was left to the imagination about any
+    reduction or increase of {125} weight. Mr. Clark does not seem to have
+    bred from brothers and sisters, which is the most injurious kind of
+    union; and he found, after repeated trials, that there was a greater
+    reduction in weight in the young from a father paired with his
+    daughter, than from a mother with her son. I may add that Mr. Eyton, of
+    Eyton, the well-known ornithologist, who is a large breeder of Grey
+    Dorkings, informs me that they certainly diminish in size, and become
+    less prolific, unless a cross with another strain is occasionally
+    obtained. So it is with Malays, according to Mr. Hewitt, as far as size
+    is concerned.[272]
+
+    An experienced writer[273] remarks that the same amateur, as is well
+    known, seldom long maintains the superiority of his birds; and this, he
+    adds, undoubtedly is due to all his stock "being of the same blood;"
+    hence it is indispensable that he should occasionally procure a bird of
+    another strain. But this is not necessary with those who keep a stock
+    of fowls at different stations. Thus, Mr. Ballance, who has bred Malays
+    for thirty years, and has won more prizes with these birds than any
+    other fancier in England, says that breeding in-and-in does not
+    necessarily cause deterioration; "but all depends upon how this is
+    managed." "My plan has been to keep about five or six distinct runs,
+    and to rear about two hundred or three hundred chickens each year, and
+    select the best birds from each run for crossing. I thus secure
+    sufficient crossing to prevent deterioration."[274]
+
+    We thus see that there is almost complete unanimity with
+    poultry-breeders that, when fowls are kept at the same place, evil
+    quickly follows from interbreeding carried on to an extent which would
+    be disregarded in the case of most quadrupeds. On the other hand, it is
+    a generally received opinion that cross-bred chickens are the hardiest
+    and most easily reared.[275] Mr. Tegetmeier, who has carefully attended
+    to poultry of all breeds, says[276] that Dorking hens, allowed to run
+    with Houdan or Crevecoeur cocks, "produce in the early spring chickens
+    that for size, hardihood, early maturity, and fitness for the market,
+    surpass those of any pure breed that we have ever raised." Mr. Hewitt
+    gives it as a general rule with fowls, that crossing the breed
+    increases their size. He makes this remark after stating that hybrids
+    from the pheasant and fowl are considerably larger than either
+    progenitor: so again, hybrids from the male golden pheasant and hen
+    common pheasant "are of far larger size than either parent-bird."[277]
+    To this subject of the increased size of hybrids I shall presently
+    return.
+
+    With _Pigeons_, breeders are unanimous, as previously stated, that it
+    is absolutely indispensable, notwithstanding the trouble and expense
+    thus caused, occasionally to cross their much-prized birds with
+    individuals of another strain, but belonging, of course, to the same
+    variety. It deserves {126} notice that, when large size is one of the
+    desired characters, as with pouters,[278] the evil effects of close
+    interbreeding are much sooner perceived than when small birds, such as
+    short-faced tumblers, are valued. The extreme delicacy of the high
+    fancy breeds, such as these tumblers and improved English carriers, is
+    remarkable; they are liable to many diseases, and often die in the egg
+    or during the first moult; and their eggs have generally to be hatched
+    under foster-mothers. Although these highly-prized birds have
+    invariably been subjected to much close interbreeding, yet their
+    extreme delicacy of constitution cannot perhaps be thus fully
+    explained. Mr. Yarrell informed me that Sir J. Sebright continued
+    closely interbreeding some owl-pigeons, until from their extreme
+    sterility he as nearly as possible lost the whole family. Mr.
+    Brent[279] tried to raise a breed of trumpeters, by crossing a common
+    pigeon, and recrossing the daughter, granddaughter,
+    great-granddaughter, and great-great-granddaughter, with the same male
+    trumpeter, until he obtained a bird with 15/16ths of trumpeter's blood;
+    but then the experiment failed, for "breeding so close stopped
+    reproduction." The experienced Neumeister[280] also asserts that the
+    offspring from dovecotes and various other breeds are "generally very
+    fertile and hardy birds:" so again, MM. Boitard and Corbie,[281] after
+    forty-five years' experience, recommend persons to cross their breeds
+    for amusement; for, if they fail to make interesting birds, they will
+    succeed under an economical point of view, "as it is found that
+    mongrels are more fertile than pigeons of pure race."
+
+    I will refer only to one other animal, namely, the Hive-bee, because a
+    distinguished entomologist has advanced this as a case of inevitable
+    close interbreeding. As the hive is tenanted by a single female, it
+    might have been thought that her male and female offspring would always
+    have bred together, more especially as bees of different hives are
+    hostile to each other; a strange worker being almost always attacked
+    when trying to enter another hive. But Mr. Tegetmeier has shown[282]
+    that this instinct does not apply to drones, which are permitted to
+    enter any hive; so that there is no _a priori_ improbability of a queen
+    receiving a foreign drone. The fact of the union invariably and
+    necessarily taking place on the wing, during the queen's nuptial
+    flight, seems to be a special provision against continued
+    interbreeding. However this may be, experience has shown, since the
+    introduction of the yellow-banded Ligurian race into Germany and
+    England, that bees freely cross: Mr. Woodbury, who introduced Ligurian
+    bees into Devonshire, found during a single season that three stocks,
+    at distances of from one to two miles from his hives, were crossed by
+    his drones. In one case the Ligurian drones must have flown over the
+    city of Exeter, and over several intermediate hives. On another
+    occasion several common black queens were crossed by Ligurian drones at
+    a distance of from one to three and a half miles.[283]
+
+{127}
+
+_Plants._
+
+    When a single plant of a new species is introduced into any country, if
+    propagated by seed, many individuals will soon be raised, so that if
+    the proper insects be present there will be crossing. With
+    newly-introduced trees or other plants not propagated by seed we are
+    not here concerned. With old-established plants it is an almost
+    universal practice occasionally to make exchanges of seed, by which
+    means individuals which have been exposed to different conditions of
+    life,--and this, as we have seen, diminishes the evil from close
+    interbreeding,--will occasionally be introduced into each district.
+
+    Experiments have not been tried on the effects of fertilising flowers
+    with their own pollen during _several_ generations. But we shall
+    presently see that certain plants, either normally or abnormally, are
+    more or less sterile, even in the first generation, when fertilised by
+    their own pollen. Although nothing is directly known on the evil
+    effects of long-continued close interbreeding with plants, the converse
+    proposition that great good is derived from crossing is well
+    established.
+
+    With respect to the crossing of individuals belonging to the same
+    sub-variety, Gaertner, whose accuracy and experience exceeded that of
+    all other hybridisers, states[284] that he has many times observed good
+    effects from this step, especially with exotic genera, of which the
+    fertility is somewhat impaired, such as Passiflora, Lobelia, and
+    Fuchsia. Herbert also says,[285] "I am inclined to think that I have
+    derived advantage from impregnating the flower from which I wished to
+    obtain seed with pollen from another individual of the same variety, or
+    at least from another flower, rather than with its own." Again,
+    Professor Lecoq asserts that he has ascertained that crossed offspring
+    are more vigorous and robust than their parents.[286]
+
+    General statements of this kind, however, can seldom be fully trusted;
+    consequently I have begun a series of experiments, which, if they
+    continue to give the same results as hitherto, will for ever settle the
+    question of the good effects of crossing two distinct plants of the
+    same variety, and of the evil effects of self-fertilisation. A clear
+    light will thus also be thrown on the fact that flowers are invariably
+    constructed so as to permit, or favour, or necessitate the union of two
+    individuals. We shall clearly understand why monoecious and
+    dioecious,--why dimorphic and trimorphic plants exist, and many other
+    such cases. The plan which I have followed in my experiments is to grow
+    plants in the same pot, or in pots of the same size, or close together
+    in the open ground; to carefully exclude insects; and then to fertilise
+    some of the flowers with pollen from the same flower, and others on the
+    same plant with pollen from a distinct but adjoining plant. In many,
+    but not all, of these experiments, the crossed plants yielded much more
+    seed than the self-fertilised plants; and I have never seen the {128}
+    reversed case. The self-fertilised and crossed seeds thus obtained were
+    allowed to germinate in the same glass vessel on damp sand; and as the
+    seeds successively germinated, they were planted in pairs on opposite
+    sides of the same pot, with a superficial partition between them, and
+    were placed so as to be equally exposed to the light. In other cases
+    the self-fertilised and crossed seeds were simply sown on opposite
+    sides of the same small pot. I have, in short, followed different
+    plans, but in every case have taken all the precautions which I could
+    think of, so that the two lots should be equally favoured. Now, I have
+    carefully observed the growth of plants raised from crossed and
+    self-fertilised seed, from their germination to maturity, in species of
+    the following genera, namely, Brassica, Lathyrus, Lupinus, Lobelia,
+    Lactuca, Dianthus, Myosotis, Petunia, Linaria, Calceolaria, Mimulus,
+    and Ipomoea, and the difference in their powers of growth, and of
+    withstanding in certain cases unfavourable conditions, was most
+    manifest and strongly marked. It is of importance that the two lots of
+    seed should be sown or planted on opposite sides of the same pot, so
+    that the seedlings may struggle against each other; for if sown
+    separately in ample and good soil, there is often but little difference
+    in their growth.
+
+    I will briefly describe the two most striking cases as yet observed by
+    me. Six crossed and six self-fertilised seeds of _Ipomoea purpurea_,
+    from plants treated in the manner above described, were planted as soon
+    as they had germinated, in pairs on opposite sides of two pots, and
+    rods of equal thickness were given them to twine up. Five of the
+    crossed plants grew from the first more quickly than the opposed
+    self-fertilised plants; the sixth, however, was weakly and was for a
+    time beaten, but at last its sounder constitution prevailed and it shot
+    ahead of its antagonist. As soon as each crossed plant reached the top
+    of its seven-foot rod its fellow was measured, and the result was that,
+    when the crossed plants were seven feet high, the self-fertilised had
+    attained the average height of only five feet four and a half inches.
+    The crossed plants flowered a little before, and more profusely than
+    the self-fertilised plants. On opposite sides of another _small_ pot a
+    large number of crossed and self-fertilised seeds were sown, so that
+    they had to struggle for bare existence; a single rod was given to each
+    lot: here again the crossed plants showed from the first their
+    advantage; they never quite reached the summit of the seven-foot rod,
+    but relatively to the self-fertilised plants their average height was
+    as seven feet to five feet two inches. The experiment was repeated in
+    the two following generations with plants raised from the
+    self-fertilised and crossed plants, treated in exactly the same manner,
+    and with nearly the same result. In the second generation, the crossed
+    plants, which were again crossed, produced 121 seed-capsules, whilst
+    the self-fertilised plants, again self-fertilised, produced only 84
+    capsules.
+
+    Some flowers of the _Mimulus luteus_ were fertilised with their own
+    pollen, and others were crossed with pollen from distinct plants
+    growing in the same pot. The seeds after germinating were thickly
+    planted on opposite sides of a pot. The seedlings were at first equal
+    in height; but when the young crossed plants were exactly half an inch,
+    the {129} self-fertilised plants were only a quarter of an inch high.
+    But this inequality did not continue, for, when the crossed plants were
+    four and a half inches high, the self-fertilised were three inches; and
+    they retained the same relative difference till their growth was
+    complete. The crossed plants looked far more vigorous than the
+    uncrossed, and flowered before them; they produced also a far greater
+    number of flowers, which yielded capsules (judging, however, from only
+    a few) containing more seeds. As in the former case, the experiment was
+    repeated in the same manner during the next two generations, and with
+    exactly the same result. Had I not watched these plants of the Mimulus
+    and Ipomoea during their whole growth, I could not have believed it
+    possible, that a difference apparently so slight, as that of the pollen
+    being taken from the same flower, and from a distinct plant growing in
+    the same small pot, could have made so wonderful a difference in the
+    growth and vigour of the plants thus produced. This, under a
+    physiological point of view, is a most remarkable phenomenon.
+
+       *       *       *       *       *
+
+    With respect to the benefit derived from crossing distinct varieties,
+    plenty of evidence has been published. Sageret[287] repeatedly speaks
+    in strong terms of the vigour of melons raised by crossing different
+    varieties, and adds that they are more easily fertilised than common
+    melons, and produce numerous good seed. Here follows the evidence of an
+    English gardener:[288] "I have this summer met with better success in
+    my cultivation of melons, in an unprotected state, from the seeds of
+    hybrids (_i.e._ mongrels) obtained by cross impregnation, than with old
+    varieties. The offspring of three different hybridisations (one more
+    especially, of which the parents were the two most dissimilar varieties
+    I could select) each yielded more ample and finer produce than any one
+    of between twenty and thirty established varieties."
+
+    Andrew Knight[289] believed that his seedlings from crossed varieties
+    of the apple exhibited increased vigour and luxuriance; and M.
+    Chevreul[290] alludes to the extreme vigour of some of the crossed
+    fruit-trees raised by Sageret.
+
+    By crossing reciprocally the tallest and shortest peas, Knight[291]
+    says, "I had in this experiment a striking instance of the stimulative
+    effects of crossing the breeds; for the smallest variety, whose height
+    rarely exceeded two feet, was increased to six feet; whilst the height
+    of the large and luxuriant kind was very little diminished." Mr. Laxton
+    gave me seed-peas produced from crosses between four distinct kinds;
+    and the plants thus raised were extraordinarily vigorous, being in each
+    case from one to two or three feet taller than the parent-forms growing
+    close alongside them.
+
+    {130}
+
+    Wiegmann[292] made many crosses between several varieties of cabbage;
+    and he speaks with astonishment of the vigour and height of the
+    mongrels, which excited the amazement of all the gardeners who beheld
+    them. Mr. Chaundy raised a great number of mongrels by planting
+    together six distinct varieties of cabbage. These mongrels displayed an
+    infinite diversity of character; "But the most remarkable circumstance
+    was, that, while all the other cabbages and borecoles in the nursery
+    were destroyed by a severe winter, these hybrids were little injured,
+    and supplied the kitchen when there was no other cabbage to be had."
+
+    Mr. Maund exhibited before the Royal Agricultural Society[293]
+    specimens of crossed wheat, together with their parent varieties; and
+    the editor states that they were intermediate in character, "united
+    with that greater vigour of growth, which it appears, in the vegetable
+    as in the animal world, is the result of a first cross." Knight also
+    crossed several varieties of wheat,[294] and he says "that in the years
+    1795 and 1796, when almost the whole crop of corn in the island was
+    blighted, the varieties thus obtained, and these only, escaped in this
+    neighbourhood, though sown in several different soils and situations."
+
+    Here is a remarkable case: M. Clotzsch[295] crossed _Pinus sylvestris_
+    and _nigricans_, _Quercus robur_ and _pedunculata, Alnus glutinosa_ and
+    _incana_, _Ulmus campestris_ and _effusa_; and the cross-fertilised
+    seeds, as well as seeds of the pure parent-trees, were all sown at the
+    same time and in the same place. The result was, that after an interval
+    of eight years, the hybrids were one-third taller than the pure trees!
+
+       *       *       *       *       *
+
+    The facts above given refer to undoubted varieties, excepting the trees
+    crossed by Clotzsch, which are ranked by various botanists as
+    strongly-marked races, sub-species, or species. That true hybrids
+    raised from entirely distinct species, though they lose in fertility,
+    often gain in size and constitutional vigour, is certain. It would be
+    superfluous to quote any facts; for all experimenters, Koelreuter,
+    Gaertner, Herbert, Sageret, Lecoq, and Naudin, have been struck with
+    the wonderful vigour, height, size, tenacity of life, precocity, and
+    hardiness of their hybrid productions. Gaertner[296] sums up his
+    conviction on this head in the strongest terms. Koelreuter[297] gives
+    numerous precise measurements of the weight and height of his hybrids
+    in comparison with measurements of both parent-forms; and speaks with
+    astonishment of their "_statura portentosa_," their "_ambitus
+    vastissimus ac altitudo valde conspicua_." Some exceptions to the rule
+    in the case of very sterile hybrids have, however, been noticed by
+    Gaertner and {131} Herbert; but the most striking exceptions are given
+    by Max Wichura,[298] who found that hybrid willows were generally
+    tender in constitution, dwarf, and short-lived.
+
+    Koelreuter explains the vast increase in the size of the roots, stems,
+    &c., of his hybrids, as the result of a sort of compensation due to
+    their sterility, in the same way as many emasculated animals are larger
+    than the perfect males. This view seems at first sight extremely
+    probable, and has been accepted by various authors;[299] but
+    Gaertner[300] has well remarked that there is much difficulty in fully
+    admitting it; for with many hybrids there is no parallelism between the
+    degree of their sterility and their increased size and vigour. The most
+    striking instances of luxuriant growth have been observed with hybrids
+    which were not sterile in any extreme degree. In the genus Mirabilis,
+    certain hybrids are unusually fertile, and their extraordinary
+    luxuriance of growth, together with their enormous roots,[301] have
+    been transmitted to their progeny. The increased size of the hybrids
+    produced between the fowl and pheasant, and between the distinct
+    species of pheasants, has been already noticed. The result in all cases
+    is probably in part due to the saving of nutriment and vital force
+    through the sexual organs not acting, or acting imperfectly, but more
+    especially to the general law of good being derived from a cross. For
+    it deserves especial attention that mongrel animals and plants, which
+    are so far from being sterile that their fertility is often actually
+    augmented, have, as previously shown, their size, hardiness, and
+    constitutional vigour generally increased. It is not a little
+    remarkable that an accession of vigour and size should thus arise under
+    the opposite contingencies of increased and diminished fertility.
+
+    It is a perfectly well ascertained fact[302] that hybrids will
+    invariably breed more readily with either pure parent, and not rarely
+    with a distinct species, than with each other. Herbert is inclined to
+    explain even this fact by the advantage derived from a cross; but
+    Gaertner more justly accounts for it by the pollen of the hybrid, and
+    probably its ovules, being in some degree vitiated, whereas the pollen
+    and ovules of both pure parents and of any third species are sound.
+    Nevertheless there are some well-ascertained and remarkable facts,
+    which, as we shall immediately see, show that the act of crossing in
+    itself undoubtedly tends to increase or re-establish the fertility of
+    hybrids.
+
+_On certain Hermaphrodite Plants which, either normally or abnormally,
+require to be fertilised by pollen from a distinct individual or species._
+
+The facts now to be given differ from those hitherto detailed, as the
+self-sterility does not here result from long-continued, {132} close
+interbreeding. These facts are, however, connected with our present
+subject, because a cross with a distinct individual is shown to be either
+necessary or advantageous. Dimorphic and trimorphic plants, though they are
+hermaphrodites, must be reciprocally crossed, one set of forms by the
+other, in order to be fully fertile, and in some cases to be fertile in any
+degree. But I should not have noticed these plants, had it not been for the
+following cases given by Dr. Hildebrand:[303]--
+
+    _Primula sinensis_ is a reciprocally dimorphic species: Dr. Hildebrand
+    fertilised twenty-eight flowers of both forms, each by pollen of the
+    other form, and obtained the full number of capsules containing on an
+    average 42.7 seed per capsule; here we have complete and normal
+    fertility. He then fertilised forty-two flowers of both forms with
+    pollen of the same form, but taken from a distinct plant, and all
+    produced capsules containing on an average only 19.6 seed. Lastly, and
+    here we come to our more immediate point, he fertilised forty-eight
+    flowers of both forms with pollen of the same form, taken from the same
+    flower, and now he obtained only thirty-two capsules, and these
+    contained on an average 18.6 seed, or one less per capsule than in the
+    former case. So that, with these illegitimate unions, the act of
+    impregnation is less assured, and the fertility slightly less, when the
+    pollen and ovules belong to the same flower, than when belonging to two
+    distinct individuals of the same form. Dr. Hildebrand has recently made
+    analogous experiments on the long-styled form of _Oxalis rosea_, with
+    the same result.[304]
+
+It has recently been discovered that certain plants, whilst growing in
+their native country under natural conditions, cannot be fertilised with
+pollen from the same plant. They are sometimes so utterly self-impotent,
+that, though they can readily be fertilised by the pollen of a distinct
+species or even distinct genus, yet, wonderful as the fact is, they never
+produce a single seed by their own pollen. In some cases, moreover, the
+plant's own pollen and stigma mutually act on each other in a deleterious
+manner. Most of the facts to be given relate to Orchids, but I will
+commence with a plant belonging to a widely different family.
+
+    Sixty-three flowers of _Corydalis cava_, borne on distinct plants, were
+    fertilised by Dr. Hildebrand[305] with pollen from other plants of the
+    same species; and fifty-eight capsules were obtained, including on an
+    average {133} 4.5 seed in each. He then fertilised sixteen flowers
+    produced by the same raceme, one with another, but obtained only three
+    capsules, one of which alone contained any good seeds, namely, two in
+    number. Lastly, he fertilised twenty-seven flowers, each with its own
+    pollen; he left also fifty-seven flowers to be spontaneously
+    fertilised, and this would certainly have ensued if it had been
+    possible, for the anthers not only touch the stigma, but the
+    pollen-tubes were seen by Dr. Hildebrand to penetrate it; nevertheless
+    these eighty-four flowers did not produce a single seed-capsule! This
+    whole case is highly instructive, as it shows how widely different the
+    action of the same pollen is, according as it is placed on the stigma
+    of the same flower, or on that of another flower on the same raceme, or
+    on that of a distinct plant.
+
+    With exotic Orchids several analogous cases have been observed, chiefly
+    by Mr. John Scott.[306] _Oncidium sphacelatum_ has effective pollen,
+    for with it Mr. Scott fertilised two distinct species; its ovules are
+    likewise capable of impregnation, for they were readily fertilised by
+    the pollen of _O. divaricatum_; nevertheless, between one and two
+    hundred flowers fertilised by their own pollen did not produce a single
+    capsule, though the stigmas were penetrated by the pollen-tubes. Mr.
+    Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also informs
+    me (1864) that a hundred and twenty flowers of this same species were
+    fertilised by him with their own pollen, and did not produce a capsule,
+    but eight flowers fertilised by the pollen of _O. divaricatum_ produced
+    four fine capsules: again, between two and three hundred flowers of _O.
+    divaricatum_, fertilised by their own pollen, did not set a capsule,
+    but twelve flowers fertilised by _O. flexuosum_ produced eight fine
+    capsules: so that here we have three utterly self-impotent species,
+    with their male and female organs perfect, as shown by their mutual
+    fertilisation. In these cases fertilisation was effected only by the
+    aid of a distinct species. But, as we shall presently see, distinct
+    plants, raised from seed, of _Oncidium flexuosum_, and probably of the
+    other species, would have been perfectly capable of fertilising each
+    other, for this is the natural process. Again, Mr. Scott found that the
+    pollen of a plant of _O. microchilum_ was good, for with it he
+    fertilised two distinct species; he found its ovules good, for they
+    could be fertilised by the pollen of one of these species, and by the
+    pollen of a distinct plant of _O. microchilum_; but they could not be
+    fertilised by pollen of the same plant, though the pollen-tubes
+    penetrated the stigma. An analogous case has been recorded by M.
+    Riviere,[307] with two plants of _O. Cavendishianum_, which were both
+    self-sterile, but reciprocally fertilised each other. All these cases
+    refer to the genus Oncidium, but Mr. Scott found that _Maxillaria
+    atro-rubens_ was "totally insusceptible of fertilisation with its own
+    pollen," but fertilised, and was fertilised by, a widely distinct
+    species, viz. _M. squalens_.
+
+    As these orchids had grown under unnatural conditions, in {134}
+    hot-houses, I concluded without hesitation that their self-sterility
+    was due to this cause. But Fritz Mueller informs me that at Desterro,
+    in Brazil, he fertilised above one hundred flowers of the
+    above-mentioned _Oncidium flexuosum_, which is there endemic, with its
+    own pollen, and with that taken from distinct plants; all the former
+    were sterile, whilst those fertilised by pollen from any _other plant_
+    of the same species were fertile. During the first three days there was
+    no difference in the action of the two kinds of pollen: that placed on
+    the stigma of the same plant separated in the usual manner into grains,
+    and emitted tubes which penetrated the column, and the stigmatic
+    chamber shut itself; but the flowers alone which had been fertilised by
+    pollen taken from a distinct plant produced seed-capsules. On a
+    subsequent occasion these experiments were repeated on a large scale
+    with the same result. Fritz Mueller found that four other endemic
+    species of Oncidium were in like manner utterly sterile with their own
+    pollen, but fertile with that from any other plant: some of them
+    likewise produced seed-capsules when impregnated with pollen of widely
+    distinct genera, such as Leptotes, Cyrtopodium, and Rodriguezia!
+    _Oncidium crispum_, however, differs from the foregoing species in
+    varying much in its self-sterility; some plants producing fine pods
+    with their own pollen, others failing to do so; in two or three
+    instances, Fritz Mueller observed that the pods produced by pollen
+    taken from a distinct flower on the same plant, were larger than those
+    produced by the flower's own pollen. In _Epidendrum cinnabarinum_, an
+    orchid belonging to another division of the family, fine pods were
+    produced by the plant's own pollen, but they contained by weight only
+    about half as much seed as the capsules which had been fertilized by
+    pollen from a distinct plant, and in one instance from a distinct
+    species; moreover, a very large proportion, and in some cases nearly
+    all the seed produced by the plant's own pollen, was embryonless and
+    worthless. Some self-fertilized capsules of a Maxillaria were in a
+    similar state.
+
+    Another observation made by Fritz Mueller is highly remarkable, namely,
+    that with various orchids the plant's own pollen not only fails to
+    impregnate the flower, but acts on the stigma, and is acted on, in an
+    injurious or poisonous manner. This is shown by the surface of the
+    stigma in contact with the pollen, and by the pollen itself, becoming
+    in from three to five days dark brown, and then decaying. The
+    discolouration and decay are not caused by parasitic cryptogams, which
+    were observed by Fritz Mueller in only a single instance. These changes
+    are well shown by placing on the same stigma, at the same time, the
+    plant's own pollen and that from a distinct plant of the same species,
+    or of another species, or even of another and widely remote genus.
+    Thus, on the stigma of _Oncidium flexuosum_, the plant's own pollen and
+    that from a distinct plant were placed side by side, and in five days'
+    time the latter was perfectly fresh, whilst the plant's own pollen was
+    brown. On the other hand, when the pollen of a distinct plant of the
+    _Oncidium flexuosum_, and of the _Epidendrum zebra_ (_nov. spec.?_),
+    were placed together on the same stigma, they behaved in exactly the
+    same manner, the grains separating, emitting tubes, and penetrating the
+    stigma, so that the two {135} pollen-masses, after an interval of
+    eleven days, could not be distinguished except by the difference of
+    their caudicles, which, of course, undergo no change. Fritz Mueller
+    has, moreover, made a large number of crosses between orchids belonging
+    to distinct species and genera, and he finds that in all cases when the
+    flowers are not fertilised their footstalks first begin to wither; and
+    the withering slowly spreads upwards until the germens fall off, after
+    an interval of one or two weeks, and in one instance of between six and
+    seven weeks; but even in this latter case, and in most other cases, the
+    pollen and stigma remained in appearance fresh. Occasionally, however,
+    the pollen becomes brownish, generally on the external surface, and not
+    in contact with the stigma, as is invariably the case when the plant's
+    own pollen is applied.
+
+    Fritz Mueller observed the poisonous action of the plant's own pollen
+    in the above-mentioned _Oncidium flexuosum_, _O. unicorne, pubes_
+    (_?_), and in two other unnamed species. Also in two species of
+    Rodriguezia, in two of Notylia, in one of Burlingtonia, and of a fourth
+    genus in the same group. In all these cases, except the last, it was
+    proved that the flowers were, as might have been expected, fertile with
+    pollen from a distinct plant of the same species. Numerous flowers of
+    one species of Notylia were fertilized with pollen from the same
+    raceme; in two days' time they all withered, the germens began to
+    shrink, the pollen-masses became dark brown, and not one pollen-grain
+    emitted a tube. So that in this orchid the injurious action of the
+    plant's own pollen is more rapid than with _Oncidium flexuosum_. Eight
+    other flowers on the same raceme were fertilized with pollen from a
+    distinct plant of the same species: two of these were dissected, and
+    their stigmas were found to be penetrated by numberless pollen-tubes;
+    and the germens of the other six flowers became well developed. On a
+    subsequent occasion many other flowers were fertilized with their own
+    pollen, and all fell off dead in a few days; whilst some flowers on the
+    same raceme which had been left simply unfertilised adhered and long
+    remained fresh. We have seen that in cross-unions between extremely
+    distinct orchids the pollen long remains undecayed; but Notylia behaved
+    in this respect differently; for when its pollen was placed on the
+    stigma of _Oncidium flexuosum_, both the stigma and pollen quickly
+    became dark brown, in the same manner as if the plant's own pollen had
+    been applied.
+
+    Fritz Mueller suggests that, as in all these cases the plant's own
+    pollen is not only impotent (thus effectually preventing
+    self-fertilization), but likewise prevents, as was ascertained in the
+    case of the Notylia and _Oncidium flexuosum_, the action of
+    subsequently applied pollen from a distinct individual, it would be an
+    advantage to the plant to have its own pollen rendered more and more
+    deleterious; for the germens would thus quickly be killed, and,
+    dropping off, there would be no further waste in nourishing a part
+    which ultimately could be of no avail. Fritz Mueller's discovery that a
+    plant's own pollen and stigma in some cases act on each other as if
+    mutually poisonous, is certainly most remarkable.
+
+We now come to cases closely analogous with those just {136} given, but
+different, inasmuch as individual plants alone of the species are
+self-impotent. This self-impotence does not depend on the pollen or ovules
+being in a state unfit for fertilisation, for both have been found
+effective in union with other plants of the same or of a distinct species.
+The fact of these plants having spontaneously acquired so peculiar a
+constitution, that they can be fertilised more readily by the pollen of a
+distinct species than by their own, is remarkable. These abnormal cases, as
+well as the foregoing normal cases, in which certain orchids, for instance,
+can be much more easily fertilised by the pollen of a distinct species than
+by their own, are exactly the reverse of what occurs with all ordinary
+species. For in these latter the two sexual elements of the same individual
+plant are capable of freely acting on each other; but are so constituted
+that they are more or less impotent when brought into union with the sexual
+elements of a distinct species, and produce more or less sterile hybrids.
+It would appear that the pollen or ovules, or both, of the individual
+plants which are in this abnormal state, have been affected in some strange
+manner by the conditions to which they themselves or their parents have
+been exposed; but whilst thus rendered self-sterile, they have retained the
+capacity common to most species of partially fertilizing and being
+partially fertilized by allied forms. However this may be, the subject, to
+a certain extent, is related to our general conclusion that good is derived
+from the act of crossing.
+
+    Gaertner experimented on two plants of _Lobelia fulgens_, brought from
+    separate places, and found[308] that their pollen was good, for he
+    fertilised with it _L. cardinalis_ and _syphilitica_; their ovules were
+    likewise good, for they were fertilised by the pollen of these same two
+    species; but these two plants of _L. fulgens_ could not be fertilised
+    by their own pollen, as can generally be effected with perfect ease
+    with this species. Again, the pollen of a plant of _Verbascum nigrum_
+    grown in a pot was found by Gaertner[309] capable of fertilising _V.
+    lychnitis_ and _V. Austriacum_; the ovules could be fertilised by the
+    pollen of _V. thapsus_; but the flowers could not be fertilised by
+    their own pollen. Koelreuter, also,[310] gives the case of three {137}
+    garden plants of _Verbascum phoeniceum_, which bore during two years
+    many flowers; these he successfully fertilised by the pollen of no less
+    than four distinct species, but they produced not a seed with their own
+    apparently good pollen; subsequently these same plants, and others
+    raised from seed, assumed a strangely fluctuating condition, being
+    temporarily sterile on the male or female side, or on both sides, and
+    sometimes fertile on both sides; but two of the plants were perfectly
+    fertile throughout the summer.
+
+    It appears[311] that certain flowers on certain plants of _Lilium
+    candidum_ can be fertilised more easily by pollen from a distinct
+    individual than by their own. So, again, with the varieties of the
+    potato. Tinzmann,[312] who made many trials with this plant, says that
+    pollen from another variety sometimes "exerts a powerful influence, and
+    I have found sorts of potatoes which would not bear seed from
+    impregnation with the pollen of their own flowers, would bear it when
+    impregnated with other pollen." It does not, however, appear to have
+    been proved that the pollen which failed to act on the flower's own
+    stigma was in itself good.
+
+    In the genus Passiflora it has long been known that several species do
+    not produce fruit, unless fertilised by pollen taken from distinct
+    species: thus, Mr. Mowbray[313] found that he could not get fruit from
+    _P. alata_ and _racemosa_ except by reciprocally fertilising them with
+    each other's pollen. Similar facts have been observed in Germany and
+    France;[314] and I have received two authentic accounts of _P.
+    quadrangularis_, which never produced fruit with its own pollen, but
+    would do so freely when fertilised in one case with the pollen of _P.
+    coerulea_, and in another case with that of _P. edulis_. So again, with
+    respect to _P. laurifolia_, a cultivator of much experience has
+    recently remarked[315] that the flowers "must be fertilised with the
+    pollen of _P. coerulea_, or of some other common kind, as their own
+    pollen will not fertilise them." But the fullest details on this
+    subject have been given by Mr. Scott:[316] plants of _Passiflora
+    racemosa_, _coerulea_, and _alata_ flowered profusely during many years
+    in the Botanic Gardens of Edinburgh, and, though repeatedly fertilised
+    by Mr. Scott and by others with their own pollen, never produced any
+    seed; yet this occurred at once with all three species when they were
+    crossed together in various ways. But in the case of _P. coerulea_,
+    three plants, two of which grew in the Botanic Gardens, were all
+    rendered fertile, merely by impregnating the one with pollen of the
+    other. The same result was attained in the same manner with _P. alata_,
+    but only with one plant out of three. As so many self-sterile species
+    have been mentioned, it may be stated that in the case of _P.
+    gracilis_, which is an annual, the flowers are nearly as fertile with
+    their own pollen as with that from a distinct plant; thus sixteen
+    flowers {138} spontaneously self-fertilised produced fruit, each
+    containing on an average 21.3 seed, whilst fruit from fourteen crossed
+    flowers contained 24.1 seed.
+
+    Returning to _P. alata_, I have received (1866) some interesting
+    details from Mr. Robinson Munro. Three plants, including one in
+    England, have already been mentioned which were inveterately
+    self-sterile, and Mr. Munro informs me of several others which, after
+    repeated trials during many years, have been found in the same
+    predicament. At some other places, however, this species fruits readily
+    when fertilised with its own pollen. At Taymouth Castle there is a
+    plant which was formerly grafted by Mr. Donaldson on a distinct
+    species, name unknown, and ever since the operation it has produced
+    fruit in abundance by its own pollen; so that this small and unnatural
+    change in the state of this plant has restored its self-fertility! Some
+    of the seedlings from the Taymouth Castle plant were found to be not
+    only sterile with their own pollen, but with each other's pollen, and
+    with the pollen of distinct species. Pollen from the Taymouth plant
+    failed to fertilise certain plants of the same species, but was
+    successful on one plant in the Edinburgh Botanic Gardens. Seedlings
+    were raised from this latter union, and some of their flowers were
+    fertilised by Mr. Munro with their own pollen; but they were found to
+    be as self-impotent as the mother-plant had always proved, except when
+    fertilised by the grafted Taymouth plant, and except, as we shall see,
+    when fertilised by her own seedlings. For Mr. Munro fertilised eighteen
+    flowers on the self-impotent mother-plant with pollen from these her
+    own self-impotent seedlings, and obtained, remarkable as the fact is,
+    eighteen fine capsules full of excellent seed! I have met with no case
+    in regard to plants which shows so well as this of _P. alata_, on what
+    small and mysterious causes complete fertility or complete sterility
+    depends.
+
+The facts hitherto given relate to the much-lessened or completely
+destroyed fertility of pure species when impregnated with their own pollen,
+in comparison with their fertility when impregnated by distinct individuals
+or distinct species; but closely analogous facts have been observed with
+hybrids.
+
+    Herbert states[317] that having in flower at the same time nine hybrid
+    Hippeastrums, of complicated origin, descended from several species, he
+    found that "almost every flower touched with pollen from another cross
+    produced seed abundantly, and those which were touched with their own
+    pollen either failed entirely, or formed slowly a pod of inferior size,
+    with fewer seeds." In the 'Horticultural Journal' he adds that, "the
+    admission of the pollen of another cross-bred Hippeastrum (however
+    complicated the cross) to any _one_ flower of the number, is almost
+    sure to check the fructification of the others." In a letter written to
+    me in 1839, Dr. Herbert says that he had already tried these
+    experiments during five consecutive years, and he subsequently repeated
+    them, with the same invariable result. {139} He was thus led to make an
+    analogous trial on a pure species, namely, on the _Hippeastrum
+    aulicum_, which he had lately imported from Brazil: this bulb produced
+    four flowers, three of which were fertilised by their own pollen, and
+    the fourth by the pollen of a triple cross between _H. bulbulosum_,
+    _reginae_, and _vittatum_; the result was, that "the ovaries of the
+    three first flowers soon ceased to grow, and after a few days perished
+    entirely: whereas the pod impregnated by the hybrid made vigorous and
+    rapid progress to maturity, and bore good seed, which vegetated
+    freely." This is, indeed, as Herbert remarks, "a strange truth," but
+    not so strange as it then appeared.
+
+    As a confirmation of these statements, I may add that Mr. M.
+    Mayes,[318] after much experience in crossing the species of Amaryllis
+    (Hippeastrum), says, "neither the species nor the hybrids will, we are
+    well aware, produce seed so abundantly from their own pollen as from
+    that of others." So, again, Mr. Bidwell, in New South Wales,[319]
+    asserts that _Amaryllis belladonna_ bears many more seeds when
+    fertilised by the pollen of _Brunswigia_ (_Amaryllis_ of some authors)
+    _Josephinae_ or of _B. multiflora_, than when fertilised by its own
+    pollen. Mr. Beaton dusted four flowers of a Cyrtanthus with their own
+    pollen, and four with the pollen of _Vallota_ (_Amaryllis_) _purpurea_;
+    on the seventh day "those which received their own pollen slackened
+    their growth, and ultimately perished; those which were crossed with
+    the Vallota held on."[320] These latter cases, however, relate to
+    uncrossed species, like those before given with respect to Passiflora,
+    Orchids, &c., and are here referred to only because the plants belong
+    to the same group of Amaryllidaceae.
+
+    In the experiments on the hybrid Hippeastrums, if Herbert had found
+    that the pollen of two or three kinds alone had been more efficient on
+    certain kinds than their own pollen, it might have been argued that
+    these, from their mixed parentage, had a closer mutual affinity than
+    the others; but this explanation is inadmissible, for the trials were
+    made reciprocally backwards and forwards on nine different hybrids; and
+    a cross, whichever way taken, always proved highly beneficial. I can
+    add a striking and analogous case from experiments made by the Rev. A.
+    Rawson, of Bromley Common, with some complex hybrids of Gladiolus. This
+    skilful horticulturist possessed a number of French varieties,
+    differing from each other only in the colour and size of the flowers,
+    all descended from Gandavensis, a well-known old hybrid, said to be
+    descended from _G. Natalensis_ by the pollen of _G.
+    oppositiflorus_.[321] Mr. Rawson, after repeated trials, found that
+    none of the varieties would set seed with their own pollen, although
+    {140} taken from distinct plants of the same variety, which had, of
+    course, been propagated by bulbs, but that they all seeded freely with
+    pollen from any other variety. To give two examples: Ophir did not
+    produce a capsule with its own pollen, but when fertilised with that of
+    Janire, Brenchleyensis, Vulcain, and Linne, it produced ten fine
+    capsules; but the pollen of Ophir was good, for when Linne was
+    fertilised by it seven capsules were produced. This later variety, on
+    the other hand, was utterly barren with its own pollen, which we have
+    seen was perfectly efficient on Ophir. Altogether, Mr. Rawson, in the
+    year 1861, fertilised twenty-six flowers borne by four varieties with
+    pollen taken from other varieties, and every single flower produced a
+    fine seed-capsule; whereas fifty-two flowers on the same plants,
+    fertilised at the same time with their own pollen, did not yield a
+    single seed-capsule. Mr. Rawson fertilised, in some cases, the
+    alternate flowers, and in other cases all those down one side of the
+    spike, with pollen of other varieties, and the remaining flowers with
+    their own pollen; I saw these plants when the capsules were nearly
+    mature, and their curious arrangement at once brought full conviction
+    to the mind that an immense advantage had been derived from crossing
+    these hybrids.
+
+    Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made
+    numerous experiments in crossing the species of Cistus, but as not yet
+    published the results, that, when any of these hybrids are fertile,
+    they may be said to be, in regard to function, dioecious; "for the
+    flowers are always sterile when the pistil is fertilised by pollen
+    taken from the same flower or from flowers on the same plant. But they
+    are often fertile if pollen be employed from a distinct individual of
+    the same hybrid nature, or from a hybrid made by a reciprocal cross."
+
+_Conclusion._--The facts just given, which show that certain plants are
+self-sterile, although both sexual elements are in a fit state for
+reproduction when united with distinct individuals of the same or other
+species, appear at first sight opposed to all analogy. The sexual elements
+of the same flower have become, as already remarked, differentiated in
+relation to each other, almost like those of two distinct species.
+
+With respect to the species which, whilst living under their natural
+conditions, have their reproductive organs in this peculiar state, we may
+conclude that it has been naturally acquired for the sake of effectually
+preventing self-fertilisation. The case is closely analous with dimorphic
+and trimorphic plants, which can be fully fertilised only by plants belong
+to the opposite form, and not, as in the foregoing cases, in differently by
+any other plant. Some of these dimorphic plants are completely sterile with
+pollen taken from the same plant or from the same {141} form. It is
+interesting to observe the graduated series from plants which, when
+fertilised by their own pollen, yield the full number of seed, but with the
+seedlings a little dwarfed in stature--to plants which when self-fertilised
+yield few seeds--to those with yield none--and, lastly, to those in which
+the plant's own pollen and stigma act on each other like poison. This
+peculiar state of the reproductive organs, when occurring in certain
+individuals alone, is evidently abnormal; and as it chiefly affects exotic
+plants, or indigenous plants cultivated in pots, we may attribute it to
+some change in the conditions of life, acting on the plants themselves or
+on their parents. The self-impotent _Passiflora alata_, which recovered its
+self-fertility after having been grafted on a distinct stock, shows how
+small a change is sufficient to act powerfully on the reproductive system.
+The possibility of a plant becoming under culture self-impotent is
+interesting as throwing light on the occurrence of this same condition in
+natural species. A cultivated plant in this state generally remains so
+during its whole life; and from this fact we may infer that the state is
+probably congenital.
+
+Koelreuter, however, has described some plants of Verbascum which varied in
+this respect even during the same season. As in all the normal cases, and
+in many, probably in most, of the abnormal cases, any two self-impotent
+plants can reciprocally fertilize each other, we may infer that a very
+slight difference in the nature of their sexual elements suffices to give
+fertility; but in other instances, as with some Passifloras and the hybrid
+Gladioli, a greater degree of differentiation appears to be necessary, for
+with these plants fertility is gained only by the union of distinct
+species, or of hybrids of distinct parentage. These facts all point to the
+same general conclusion, namely, that good is derived from a cross between
+individuals, which either innately, or from exposure to dissimilar
+conditions, have come to differ in sexual constitution.
+
+Exotic animals confined in menageries are sometimes in nearly the same
+state as the above-described self-impotent plants; for, as we shall see in
+the following chapter, certain monkeys, the larger carnivora, several
+finches, geese, and pheasants, cross together, quite as freely as, or even
+more freely than, the individuals of the same species breed together. Cases
+will, {142} also, be given of sexual incompatibility between certain male
+and female domesticated animals, which, nevertheless, are fertile when
+matched with any other individual of the same kind.
+
+In the early part of this chapter it was shown that the crossing of
+distinct forms, whether closely or distantly allied, gives increased size
+and constitutional vigour, and, except in the case of crossed species,
+increased fertility, to the offspring. The evidence rests on the universal
+testimony of breeders (for it should be observed that I am not here
+speaking of the evil results of close interbreeding), and is practically
+exemplified in the higher value of cross-bred animals for immediate
+consumption. The good results of crossing have also been demonstrated, in
+the case of some animals and of numerous plants, by actual weight and
+measurement. Although animals of pure blood will obviously be deteriorated
+by crossing, as far as their characteristic qualities are concerned, there
+seems to be no exception to the rule that advantages of the kind just
+mentioned are thus gained, even when there has not been any previous close
+interbreeding. The rule applies to all animals, even to cattle and sheep,
+which can long resist breeding in-and-in between the nearest
+blood-relations. It applies to individuals of the same sub-variety but of
+distinct families, to varieties or races, to sub-species, as well as to
+quite distinct species.
+
+In this latter case, however, whilst size, vigour, precocity, and hardiness
+are, with rare exceptions, gained, fertility, in a greater or less degree,
+is lost; but the gain cannot be exclusively attributed to the principle of
+compensation; for there is no close parallelism between the increased size
+and vigour of the offspring and their sterility. Moreover it has been
+clearly proved that mongrels which are perfectly fertile gain these same
+advantages as well as sterile hybrids.
+
+The evil consequences of long-continued close interbreeding are not so
+easily recognised as the good effects from crossing, for the deterioration
+is gradual. Nevertheless it is the general opinion of those who have had
+most experience, especially with animals which propagate quickly, that evil
+does inevitably follow sooner or later, but at different rates with
+different animals. No doubt a false belief may widely prevail like a
+superstition; yet it is difficult to suppose that so many acute and
+original {143} observers have all been deceived at the expense of much cost
+and trouble. A male animal may sometimes be paired with his daughter,
+granddaughter, and so on, even for seven generations, without any manifest
+bad result; but the experiment has never been tried of matching brothers
+and sisters, which is considered the closest form of interbreeding, for an
+equal number of generations. There is good reason to believe that by
+keeping the members of the same family in distinct bodies, especially if
+exposed to somewhat different conditions of life, and by occasionally
+crossing these families, the evil results may be much diminished, or quite
+eliminated. These results are loss of constitutional vigour, size, and
+fertility; but there is no necessary deterioration in the general form of
+the body, or in other good qualities. We have seen that with pigs
+first-rate animals have been produced after long-continued close
+interbreeding, though they had become extremely infertile when paired with
+their near relations. The loss of fertility, when it occurs, seems never to
+be absolute, but only relative to animals of the same blood; so that this
+sterility is to a certain extent analogous with that of self-impotent
+plants which cannot be fertilised by their own pollen, but are perfectly
+fertile with pollen of any other plant of the same species. The fact of
+infertility of this peculiar nature being one of the results of
+long-continued interbreeding, shows that interbreeding does not act merely
+by combining and augmenting various morbid tendencies common to both
+parents; for animals with such tendencies, if not at the time actually ill,
+can generally propagate their kind. Although offspring descended from the
+nearest blood-relations are not necessarily deteriorated in structure, yet
+some authors[322] believe that they are eminently liable to malformations;
+and this is not improbable, as everything which lessens the vital powers
+acts in this manner. Instances of this kind have been recorded in the case
+of pigs, bloodhounds, and some other animals.
+
+Finally, when we consider the various facts now given which plainly show
+that good follows from crossing, and less plainly {144} that evil follows
+from close interbreeding, and when we bear in mind that throughout the
+whole organic world elaborate provision has been made for the occasional
+union of distinct individuals, the existence of a great law of nature is,
+if not proved, at least rendered in the highest degree probable; namely,
+that the crossing of animals and plants which are not closely related to
+beach other is highly beneficial or even necessary, and that interbreeding
+prolonged during many generations is highly injurious.
+
+       *       *       *       *       *
+
+
+{145}
+
+CHAPTER XVIII.
+
+ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:
+STERILITY FROM VARIOUS CAUSES.
+
+    ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF
+    LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE
+    COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF
+    SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF
+    STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM CHANGED
+    CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF
+    PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE
+    ANTHERS--MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE
+    FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE DEVELOPMENT OF
+    THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY
+    BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND
+    SEEDLESS FRUIT.
+
+_On the Good derived from slight Changes in the Conditions of Life._--In
+considering whether any facts were known which might throw light on the
+conclusion arrived at in the last chapter, namely, that benefits ensue from
+crossing, and that it is a law of nature that all organic beings should
+occasionally cross, it appeared to me probable that the good derived from
+slight changes in the conditions of life, from being an analogous
+phenomenon, might serve this purpose. No two individuals, and still less no
+two varieties, are absolutely alike in constitution and structure; and when
+the germ of one is fertilised by the male element of another, we may
+believe that it is acted on in a somewhat similar manner as an individual
+when exposed to slightly changed conditions. Now, every one must have
+observed the remarkable influence on convalescents of a change of
+residence, and no medical man doubts the truth of this fact. Small farmers
+who hold but little land are convinced that their cattle derive great
+benefit from a change of pasture. In the case of plants, the evidence is
+strong that a great advantage is derived from exchanging seeds, tubers,
+bulbs, and cuttings from one soil or place to another as different as
+possible. {146}
+
+    The belief that plants are thus benefited, whether or not well founded,
+    has been firmly maintained from the time of Columella, who wrote
+    shortly after the Christian era, to the present day; and it now
+    prevails in England, France, and Germany.[323] A sagacious observer,
+    Bradley, writing in 1724,[324] says, "When we once become Masters of a
+    good Sort of Seed, we should at least put it into Two or Three Hands,
+    where the Soils and Situations are as different as possible; and every
+    Year the Parties should change with one another; by which Means, I find
+    the Goodness of the Seed will be maintained for several Years. For Want
+    of this Use many Farmers have failed in their Crops and been great
+    Losers." He then gives his own practical experience on this head. A
+    modern writer[325] asserts, "Nothing can be more clearly established in
+    agriculture than that the continual growth of any one variety in the
+    same district makes it liable to deterioration either in quality or
+    quantity." Another writer states that he sowed close together in the
+    same field two lots of wheat-seed, the product of the same original
+    stock, one of which had been grown on the same land, and the other at a
+    distance, and the difference in favour of the crop from the latter seed
+    was remarkable. A gentleman in Surrey who has long made it his business
+    to raise wheat to sell for seed, and who has constantly realised in the
+    market higher prices than others, assures me that he finds it
+    indispensable continually to change his seed; and that for this purpose
+    he keeps two farms differing much in soil and elevation.
+
+    With respect to the tubers of the potato, I find that at the present
+    day the practice of exchanging sets is almost everywhere followed. The
+    great growers of potatoes in Lancashire formerly used to get tubers
+    from Scotland, but they found that "a change from the moss-lands, and
+    _vice versa_, was generally sufficient." In former times in France the
+    crop of potatoes in the Vosges had become reduced in the course of
+    fifty or sixty years in the proportion from 120-150 to 30-40 bushels;
+    and the famous Oberlin attributed the surprising good which he effected
+    in large part to changing the sets.[326]
+
+    A well-known practical gardener, Mr. Robson[327] positively states that
+    he has himself witnessed decided advantage from obtaining bulbs of the
+    onion, tubers of the potato, and various seeds, all of the same kind,
+    from different soils and distant parts of England. He further states
+    that with {147} plants propagated by cuttings, as with the Pelargonium,
+    and especially the Dahlia, manifest advantage is derived from getting
+    plans of the same variety, which have been cultivated in another place;
+    or, "where the extent of the place allows, to take cuttings from one
+    description of soil to plant on another, so as to afford the change
+    that seems so necessary to the well-being of the plants." He maintains
+    that after a time an exchange of this nature is "forced on the grower,
+    whether he be prepared for it or not." Similar remarks have been made
+    by another excellent gardener, Mr. Fish, namely, that cuttings of the
+    same variety of Calceolaria, which he obtained from a neighbour,
+    "showed much greater vigour than some of his own that were treated in
+    exactly the same manner," and he attributed this solely to his own
+    plants having become "to a certain extent worn out or tired of their
+    quarters." Something of this kind apparently occurs in grafting and
+    budding fruit-trees; for, according to Mr. Abbey, grafts or buds
+    generally take on a distinct variety or even species, or on a stock
+    previously grafted, with greater facility than on stocks raised from
+    seeds of the variety which is to be grafted; and he believes this
+    cannot be altogether explained by the stocks in question being better
+    adapted to the soil and climate of the place. It should, however, be
+    added, that varieties grafted or budded on very distinct kinds, though
+    they may take more readily and grow at first more vigorously than when
+    grafted on closely allied stocks, afterwards often become unhealthy.
+
+    I have studied M. Tessier's careful and elaborate experiments,[328]
+    made to disprove the common belief that good is derived from a change
+    of seed; and he certainly shows that the same seed may with care be
+    cultivated on the same farm (it is not stated whether on exactly the
+    same soil) for ten consecutive years without loss. Another excellent
+    observer, Colonel Le Couteur,[329] has come to the same conclusion; but
+    then he expressly adds, if the same seed be used, "that which is grown
+    on land manured from the mixen one year becomes seed for land prepared
+    with lime, and that again becomes seed for land dressed with ashes,
+    then for land dressed with mixed manure, and so on." But this in effect
+    is a systematic exchange of seed, within the limits of the same farm.
+
+On the whole the belief, which has long been held by many skilful
+cultivators, that good follows from exchanging seed, tubers, &c., seems to
+be fairly well founded. Considering the small size of most seeds, it seems
+hardly credible that the advantage thus derived can be due to the seeds
+obtaining in one soil some chemical element deficient in the other soil. As
+plants after once germinating naturally become fixed to the same spot, it
+might have been anticipated that they would show the good effects of a
+change more plainly than animals, which continually wander about; and this
+apparently is the {148} case. Life depending on, or consisting in, an
+incessant play of the most complex forces, it would appear that their
+action is in some way stimulated by slight changes in the circumstances to
+which each organism is exposed. All forces throughout nature, as Mr.
+Herbert Spencer[330] remarks, tend towards an equilibrium, and for the life
+of each being it is necessary that this tendency should be checked. If
+these views and the foregoing facts can be trusted, they probably throw
+light, on the one hand, on the good effects of crossing the breed, for the
+germ will be thus slightly modified or acted on by new forces; and on the
+other hand, on the evil effects of close interbreeding prolonged during
+many generations, during which the germ will be acted on by a male having
+almost identically the same constitution.
+
+_Sterility from changed Conditions of Life._
+
+I will now attempt to show that animals and plants, when removed from their
+natural conditions, are often rendered in some degree infertile or
+completely barren; and this occurs even when the conditions have not been
+greatly changed. This conclusion is not necessarily opposed to that at
+which we have just arrived, namely, that lesser changes of other kinds are
+advantageous to organic beings. Our present subject is of some importance,
+from having an intimate connexion with the causes of variability.
+Indirectly it perhaps bears on the sterility of species when crossed: for
+as, on the one hand, slight changes in the conditions of life are
+favourable to plants and animals, and the crossing of varieties adds to the
+size, vigour, and fertility of their offspring; so, on the other hand,
+certain other changes in the conditions of life cause sterility; and as
+this likewise ensues from crossing much-modified forms or species, we have
+a parallel and double series of facts, which apparently stand in close
+relation to each other.
+
+It is notorious that many animals, though perfectly tamed, {149} refuse to
+breed in captivity. Isidore Geoffroy St. Hilaire[331] consequently has
+drawn a broad distinction between tamed animals which will not breed under
+captivity, and truly domesticated animals which breed freely--generally
+more freely, as shown in the sixteenth chapter, than in a state of nature.
+It is possible and generally easy to tame most animals; but experience has
+shown that it is difficult to get them to breed regularly, or even at all.
+I shall discuss this subject in detail; but will give only those cases
+which seem most illustrative. My materials are derived from notices
+scattered through various works, and especially from a Report, drawn up for
+me by the kindness of the officers of the Zoological Society of London,
+which has especial value, as it records all the cases, during nine years
+from 1838-46, in which the animals were seen to couple but produced no
+offspring, as well as the cases in which they never, as far as known,
+coupled. This MS. Report I have corrected by the annual Reports
+subsequently published. Many facts are given on the breeding of the animals
+in that magnificent work, 'Gleanings from the Menageries of Knowsley Hall,'
+by Dr. Gray. I made, also, particular inquiries from the experienced keeper
+of the birds in the old Surrey Zoological Gardens. I should premise that a
+slight change in the treatment of animals sometimes makes a great
+difference in their fertility; and it is probable that the results observed
+in different menageries would differ. Indeed some animals in our Zoological
+Gardens have become more productive since the year 1846. It is, also,
+manifest from F. Cuvier's account of the Jardin des Plantes,[332] that the
+animals formerly bred much less freely there than with us; for instance, in
+the Duck tribe, which is highly prolific, only one species had at that
+period produced young.
+
+    The most remarkable cases, however, are afforded by animals kept in
+    their native country, which, though perfectly tamed, quite healthy, and
+    allowed some freedom, are absolutely incapable of breeding.
+    Rengger,[333] who in Paraguay particularly attended to this subject,
+    specifies six quadrupeds in this condition; and he mentions two or
+    three others which most rarely {150} breed. Mr. Bates, in his admirable
+    work on the Amazons, strongly insists on similar cases;[334] and he
+    remarks, that the fact of thoroughly tamed native mammals and birds not
+    breeding when kept by the Indians, cannot be wholly accounted for by
+    their negligence or indifference, for the turkey is valued by them, and
+    the fowl has been adopted by the remotest tribes. In almost every part
+    of the world--for instance, in the interior of Africa, and in several
+    of the Polynesian islands--the natives are extremely fond of taming the
+    indigenous quadrupeds and birds; but they rarely or never succeed in
+    getting them to breed.
+
+    The most notorious case of an animal not breeding in captivity is that
+    of the elephant. Elephants are kept in large numbers in their native
+    Indian home, live to old age, and are vigorous enough for the severest
+    labour; yet, with one or two exceptions, they have never been known
+    even to couple, though both males and females have their proper
+    periodical seasons. If, however, we proceed a little eastward to Ava,
+    we hear from Mr. Crawfurd[335] that their "breeding in the domestic
+    state, or at least in the half-domestic state in which the female
+    elephants are generally kept, is of every-day occurrence;" and Mr.
+    Crawfurd informs me that he believes that the difference must be
+    attributed solely to the females being allowed to roam the forests with
+    some degree of freedom. The captive rhinoceros, on the other hand,
+    seems from Bishop Heber's account[336] to breed in India far more
+    readily than the elephant. Four wild species of the horse genus have
+    bred in Europe, though here exposed to a great change in their natural
+    habits of life; but the species have generally been crossed one with
+    another. Most of the members of the pig family breed readily in our
+    menageries: even the Red River hog (_Potamochoerus penicillatus_), from
+    the sweltering plains of West Africa, has bred twice in the Zoological
+    Gardens. Here also the Peccary (_Dicotyles torquatus_) has bred several
+    times; but another species, the _D. labiatus_, though rendered so tame
+    as to be half-domesticated, breeds so rarely in its native country of
+    Paraguay, that according to Rengger[337] the fact requires
+    confirmation. Mr. Bates remarks that the tapir, though often kept tame
+    in Amazonia by the Indians, never breeds.
+
+    Ruminants generally breed quite freely in England, though brought from
+    widely different climates, as may be seen in the Annual Reports of the
+    Zoological Gardens, and in the Gleanings from Lord Derby's menagerie.
+
+    The Carnivora, with the exception of the Plantigrade division,
+    generally breed (though with capricious exceptions) almost as freely as
+    ruminants. Many species of Felidae have bred in various menageries,
+    although imported from various climates and closely confined. Mr.
+    Bartlett, the present superintendent of the Zoological Gardens,[338]
+    remarks that the lion appears to breed more frequently and to bring
+    forth more young at a birth than any other species of the family. He
+    adds that the tiger has rarely bred; {151} "but there are several
+    well-authenticated instances of the female tiger breeding with the
+    lion." Strange as the fact may appear, many animals under confinement
+    unite with distinct species and produce hybrids quite as freely as, or
+    even more freely than, with their own species. On inquiring from Dr.
+    Falconer and others, it appears that the tiger when confined in India
+    does not breed, though it has been known to couple. The cheetah (_Felis
+    jubata_) has never been known by Mr. Bartlett to breed in England, but
+    it has bred at Frankfort; nor does it breed in India, where it is kept
+    in large numbers for hunting; but no pains would be taken to make them
+    breed, as only those animals which have hunted for themselves in a
+    state of nature are serviceable and worth training.[339] According to
+    Rengger, two species of wild cats in Paraguay, though thoroughly tamed,
+    have never bred. Although so many of the Felidae breed readily in the
+    Zoological Gardens, yet conception by no means always follows union: in
+    the nine-year Report, various species are specified which were observed
+    to couple seventy-three times, and no doubt this must have passed many
+    times unnoticed; yet from the seventy-three unions only fifteen births
+    ensued. The Carnivora in the Zoological Gardens were formerly less
+    freely exposed to the air and cold than at present, and this change of
+    treatment, as I was assured by the former superintendent, Mr. Miller,
+    greatly increased their fertility. Mr. Bartlett, and there cannot be a
+    more capable judge, says, "it is remarkable that lions breed more
+    freely in travelling collections than in the Zoological Gardens;
+    probably the constant excitement and irritation produced by moving from
+    place to place, or change of air, may have considerable influence in
+    the matter."
+
+    Many members of the Dog family breed readily when confined. The Dhole
+    is one of the most untameable animals in India, yet a pair kept there
+    by Dr. Falconer produced young. Foxes, on the other hand, rarely breed,
+    and I have never heard of such an occurrence with the European fox: the
+    silver fox of North America (_Canis argentatus_), however, has bred
+    several times in the Zoological Gardens. Even the otter has bred there.
+    Every one knows how readily the semi-domesticated ferret breeds, though
+    shut up in miserably small cages; but other species of Viverra and
+    Paradoxurus absolutely refuse to breed in the Zoological Gardens. The
+    Genetta has bred both here and in the Jardin des Plantes, and produced
+    hybrids. The _Herpestes fasciatus_ has likewise bred; but I was
+    formerly assured that the _H. griseus_, though many were kept in the
+    Gardens, never bred.
+
+    The Plantigrade Carnivora breed under confinement much less freely,
+    without our being able to assign any reason, than other members of the
+    group. In the nine-year Report it is stated that the bears had been
+    seen in the Zoological Gardens to couple freely, but previously to 1848
+    had most rarely conceived. In the Reports published since this date
+    three species have produced young (hybrids in one case), and, wonderful
+    to relate, the white Polar bear has produced young. The badger (_Meles
+    taxus_) has bred several times in the Gardens; but I have not heard of
+    this {152} occurring elsewhere in England, and the event must be very
+    rare, for an instance in Germany has been thought worth recording.[340]
+    In Paraguay the native Nasua, though kept in pairs during many years
+    and perfectly tamed, has never been known, according to Rengger, to
+    breed or show any sexual passion; nor, as I hear from Mr. Bates, does
+    this animal, or the Cercoleptes, breed in the region of the Amazons.
+    Two other plantigrade genera, Procyon and Gulo, though often kept tame
+    in Paraguay, never breed there. In the Zoological Gardens species of
+    Nasua and Procyon have been seen to couple; but they did not produce
+    young.
+
+    As domesticated rabbits, guinea-pigs, and white mice breed so
+    abundantly when closely confined under various climates, it might have
+    been thought that most other members of the Rodent order would have
+    bred in captivity, but this is not the case. It deserves notice, as
+    showing how the capacity to breed sometimes goes by affinity, that the
+    one native rodent of Paraguay, which there breeds _freely_ and has
+    yielded successive generations, is the _Cavia aperea_; and this animal
+    is so closely allied to the guinea-pig, that it has been erroneously
+    thought to be the parent-form.[341] In the Zoological Gardens, some
+    rodents have coupled, but have never produced young; some have neither
+    coupled nor bred; but a few have bred, as the porcupine more than once,
+    the Barbary mouse, lemming, chinchilla, and the agouti (_Dasyprocta
+    aguti_), several times. This latter animal has also produced young in
+    Paraguay, though they were born dead and ill-formed; but in Amazonia,
+    according to Mr. Bates, it never breeds, though often kept tame about
+    the houses. Nor does the paca (_Coelogenys paca_) breed there. The
+    common hare when confined has, I believe, never bred in Europe;[342]
+    though, according to a recent statement, it has crossed with the
+    rabbit. I have never heard of the dormouse breeding in confinement. But
+    squirrels offer a more curious case: with one exception, no species has
+    ever bred in the Zoological Gardens, yet as many as fourteen
+    individuals of _S. palmarum_ were kept together during several years.
+    The _S. cinerea_ has been seen to couple, but it did not produce young;
+    nor has this species, when rendered extremely tame in its native
+    country, North America, been ever known to breed.[343] At Lord Derby's
+    menagerie squirrels of many kinds were kept in numbers, but Mr.
+    Thompson, the superintendent, told me that none had ever bred there, or
+    elsewhere as far as he knew. I have never heard of the English squirrel
+    breeding in confinement. But the species which has bred more than once
+    in the Zoological Gardens is the one which perhaps might have been
+    least expected, namely, the flying squirrel (_Sciuropterus volucella_):
+    it has, also, bred several times {153} near Birmingham; but the female
+    never produced more than two young at a birth, whereas in its native
+    American home she bears from three to six young.[344]
+
+    Monkeys, in the nine-year Report from the Zoological Gardens, are
+    stated to unite most freely, but during this period, though many
+    individuals were kept, there were only seven births. I have heard of
+    one American monkey alone, the Ouistiti, breeding in Europe.[345] A
+    Macacus, according to Flourens, bred in Paris; and more than one
+    species of this genus has produced young in London, especially the
+    _Macacus rhesus_, which everywhere shows a special capacity to breed
+    under confinement. Hybrids have been produced both in Paris and London
+    from this same genus. The Arabian baboon, or _Cynocephalus
+    hamadryas_,[346] and a Cercopithecus have bred in the Zoological
+    Gardens, and the latter species at the Duke of Northumberland's.
+    Several members of the family of Lemurs have produced hybrids in the
+    Zoological Gardens. It is much more remarkable that monkeys very rarely
+    breed when confined in their native country; thus the Cay (_Cebus
+    azarae_) is frequently and completely tamed in Paraguay, but
+    Rengger[347] says that it breeds so rarely, that he never saw more than
+    two females which had produced young. A similar observation has been
+    made with respect to the monkeys which are frequently tamed by the
+    aborigines in Brazil.[348] In the region of the Amazons, these animals
+    are so often kept in a tame state, that Mr. Bates in walking through
+    the streets of Para counted thirteen species; but, as he asserts, they
+    have never been known to breed in captivity.[349]
+
+_Birds._
+
+    Birds offer in some respects better evidence than quadrupeds, from
+    their breeding more rapidly and being kept in greater numbers. We have
+    seen that carnivorous animals are more fertile under confinement than
+    most other mammals. The reverse holds good with carnivorous birds. It
+    is said[350] that as many as eighteen species have been used in Europe
+    for hawking, and several others in Persia and India;[351] they have
+    been kept in their native country in the finest condition, and have
+    been flown during six, eight, or nine years;[352] yet there is no
+    record of their having ever produced young. As these birds were
+    formerly caught whilst young, at great expense, being imported from
+    Iceland, Norway, and Sweden, there can {154} be little doubt that, if
+    possible, they would have been propagated. In the Jardin des Plantes,
+    no bird of prey has been known to couple.[353] No hawk, vulture, or owl
+    has ever produced fertile eggs in the Zoological Gardens, or in the old
+    Surrey Gardens, with the exception, in the former place on one
+    occasion, of a condor and a kite (_Milvus niger_). Yet several species,
+    namely, the _Aquila fusca_, _Haliaetus leucocephalus_, _Falco
+    tinnunculus_, _F. subbuteo_, and _Buteo vulgaris_, have been seen to
+    couple in the Zoological Gardens. Mr. Morris[354] mentions as a unique
+    fact that a kestrel (_Falco tinnunculus_) bred in an aviary. The one
+    kind of owl which has been known to couple in the Zoological Gardens
+    was the Eagle Owl (_Bubo maximus_); and this species shows a special
+    inclination to breed in captivity; for a pair at Arundel Castle, kept
+    more nearly in a state of nature "than ever fell to the lot of an
+    animal deprived of its liberty,"[355] actually reared their young. Mr.
+    Gurney has given another instance of this same owl breeding in
+    confinement; and he records the case of a second species of owl, the
+    _Strix passerina_, breeding in captivity.[356]
+
+    Of the smaller graminivorous birds, many kinds have been kept tame in
+    their native countries, and have lived long; yet, as the highest
+    authority on cage-birds[357] remarks, their propagation is "uncommonly
+    difficult." The canary-bird shows that there is no inherent difficulty
+    in these birds breeding freely in confinement; and Audubon says[358]
+    that the _Fringilla_ (_Spiza_) _ciris_ of North America breeds as
+    perfectly as the canary. The difficulty with the many finches which
+    have been kept in confinement is all the more remarkable as more than a
+    dozen species could be named which have yielded hybrids with the
+    canary; but hardly any of these, with the exception of the siskin
+    (_Fringilla spinus_), have reproduced their own kind. Even the
+    bullfinch (_Loxia pyrrhula_) has bred as frequently with the canary,
+    though belonging to a distinct genus, as with its own species.[359]
+    With respect to the skylark (_Alauda arvensis_), I have heard of birds
+    living for seven years in an aviary, which never produced young; and a
+    great London bird-fancier assured me that he had never known an
+    instance of their breeding; nevertheless one case has been
+    recorded.[360] In the nine-year Report from the Zoological Society,
+    twenty-four incessorial species are enumerated which had not bred, and
+    of these only four were known to have coupled.
+
+    Parrots are singularly long-lived birds; and Humboldt mentions the
+    curious fact of a parrot in South America, which spoke the language of
+    {155} an extinct Indian tribe, so that this bird preserved the sole
+    relic of a lost language. Even in this country there is reason to
+    believe[361] that parrots have lived to the age of nearly one hundred
+    years; yet, though many have been kept in Europe, they breed so rarely
+    that the event has been thought worth recording in the gravest
+    publications.[362] According to Bechstein[363] the African _Psittacus
+    erithacus_ breeds oftener than any other species: the _P. macoa_
+    occasionally lays fertile eggs, but rarely succeeds in hatching them;
+    this bird, however, has the instinct of incubation sometimes so
+    strongly developed, that it will hatch the eggs of fowls or pigeons. In
+    the Zoological Gardens and in the old Surrey Gardens some few species
+    have coupled, but, with the exception of three species of parrakeets,
+    none have bred. It is a much more remarkable fact that in Guiana
+    parrots of two kinds, as I am informed by Sir E. Schomburgk, are often
+    taken from the nests by the Indians and reared in large numbers; they
+    are so tame that they fly freely about the houses, and come when called
+    to be fed, like pigeons; yet he has never heard of a single instance of
+    their breeding.[364] In Jamaica, a resident naturalist, Mr. R.
+    Hill,[365] says, "no birds more readily submit to human dependence than
+    the parrot-tribe, but no instance of a parrot breeding in this tame
+    life has been known yet." Mr. Hill specifies a number of other native
+    birds kept tame in the West Indies, which never breed in this state.
+
+    The great pigeon family offers a striking contrast with parrots: in the
+    nine-year Report thirteen species are recorded as having bred, and,
+    what is more noticeable, only two were seen to couple without any
+    result. Since the above date every annual Report gives many cases of
+    various pigeons breeding. The two magnificent crowned pigeons (_Goura
+    coronata_ and _Victoriae_) produced hybrids; nevertheless, of the
+    former species more than a dozen birds were kept, as I am informed by
+    Mr. Crawfurd, in a park at Penang, under a perfectly well-adapted
+    climate, but never once bred. The _Columba migratoria_ in its native
+    country, North America, invariably lays two eggs, but in Lord Derby's
+    menagerie never more than one. The same fact has been observed with the
+    _C. leucocephala_.[366]
+
+    Gallinaceous birds of many genera likewise show an eminent capacity for
+    breeding under captivity. This is particularly the case with pheasants;
+    yet our English species seldom lays more than ten eggs in confinement;
+    whilst from eighteen to twenty is the usual number in the wild
+    state.[367] With the Gallinaceae, as with all other orders, there are
+    marked and {156} inexplicable exceptions in regard to the fertility of
+    certain species and genera under confinement. Although many trials have
+    been made with the common partridge, it has rarely bred, even when
+    reared in large aviaries; and the hen will never hatch her own
+    eggs.[368] The American tribe of Guans or Cracidae are tamed with
+    remarkable ease, but are very shy breeders in this country;[369] but
+    with care various species were formerly made to breed rather freely in
+    Holland.[370] Birds of this tribe are often kept in a perfectly tamed
+    condition in their native country by the Indians, but they never
+    breed.[371] It might have been expected that grouse from their habits
+    of life would not have bred in captivity, more especially as they are
+    said soon to languish and die.[372] But many cases are recorded of
+    their breeding: the capercailzie (_Tetrao urogallus_) has bred in the
+    Zoological Gardens; it breeds without much difficulty when confined in
+    Norway, and in Russia five successive generations have been reared:
+    _Tetrao tetrix_ has likewise bred in Norway; _T. Scoticus_ in Ireland;
+    _T. umbellus_ at Lord Derby's; and _T. cupido_ in North America.
+
+    It is scarcely possible to imagine a greater change in habits than that
+    which the members of the ostrich family must suffer, when cooped up in
+    small enclosures under a temperate climate, after freely roaming over
+    desert and tropical plains or entangled forests. Yet almost all the
+    kinds, even the mooruk (_Casuarius  Bennettii_) from New Ireland, has
+    frequently produced young in the various European menageries. The
+    African ostrich, though perfectly healthy and living long in the South
+    of France, never lays more than from twelve to fifteen eggs, though in
+    its native country it lays from twenty-five to thirty.[373] Here we
+    have another instance of fertility impaired, but not lost, under
+    confinement, as with the flying squirrel, the hen-pheasant, and two
+    species of American pigeons.
+
+    Most Waders can be tamed, as the Rev. E. S. Dixon informs me, with
+    remarkable facility; but several of them are short-lived under
+    confinement, so that their sterility in this state is not surprising.
+    The cranes breed more readily than other genera: _Grus montigresia_ has
+    bred several times in Paris and in the Zoological Gardens, as has _G.
+    cinerea_ at the latter place, and _G. antigone_ at Calcutta. Of other
+    members of this great order, _Tetrapteryx paradisea_ has bred at
+    Knowsley, a Porphyrio in Sicily, and the _Gallinula chloropus_ in the
+    Zoological Gardens. On the other hand, several {157} birds belonging to
+    this order will not breed in their native country, Jamaica; and the
+    Psophia, though often kept by the Indians of Guiana about their houses,
+    "is seldom or never known to breed."[374]
+
+    No birds breed with such complete facility under confinement as the
+    members of the great Duck family; yet, considering their aquatic and
+    wandering habits, and the nature of their food, this could not have
+    been anticipated. Even some time ago above two dozen species had bred
+    in the Zoological Gardens; and M. Selys-Longchamps has recorded the
+    production of hybrids from forty-four different members of the family;
+    and to these Professor Newton has added a few more cases.[375] "There
+    is not," says Mr. Dixon,[376] "in the wide world, a goose which is not
+    in the strict sense of the word domesticable;" that is, capable of
+    breeding under confinement; but this statement is probably too bold.
+    The capacity to breed sometimes varies in individuals of the same
+    species; thus Audubon[377] kept for more than eight years some wild
+    geese (_Anser Canadensis_), but they would not mate; whilst other
+    individuals of the same species produced young during the second year.
+    I know of but one instance in the whole family of a species which
+    absolutely refuses to breed in captivity, namely, the _Dendrocygna
+    viduata_, although, according to Sir R. Schomburgk,[378] it is easily
+    tamed, and is frequently kept by the Indians of Guiana. Lastly, with
+    respect to Gulls, though many have been kept in the Zoological Gardens
+    and in the old Surrey Gardens, no instance was known before the year
+    1848 of their coupling or breeding; but since that period the herring
+    gull (_Larus argentatus_) has bred many times in the Zoological Gardens
+    and at Knowsley.
+
+    There is reason to believe that insects are affected by confinement
+    like the higher animals. It is well known that the Sphingidae rarely
+    breed when thus treated. An entomologist[379] in Paris kept twenty-five
+    specimens of _Saturnia pyri_, but did not succeed in getting a single
+    fertile egg. A number of females of _Orthosia munda_ and of _Mamestra
+    suasa_ reared in confinement were unattractive to the males.[380] Mr.
+    Newport kept nearly a hundred individuals of two species of Vanessa,
+    but not one paired; this, however, might have been due to their habit
+    of coupling on the wing.[381] Mr. Atkinson could never succeed in India
+    in making the Tarroo silk-moth breed in confinement.[382] It appears
+    that a number of moths, especially the Sphingidae, when hatched in the
+    autumn out of their proper season, {158} are completely barren; but
+    this latter case is still involved in some obscurity.[383]
+
+Independently of the fact of many animals under confinement not coupling,
+or, if they couple, not producing young, there is evidence of another kind,
+that their sexual functions are thus disturbed. For many cases have been
+recorded of the loss by male birds when confined of their characteristic
+plumage. Thus the common linnet (_Linota cannabina_) when caged does not
+acquire the fine crimson colour on its breast, and one of the buntings
+(_Emberiza passerina_) loses the black on its head. A Pyrrhula and an
+Oriolus have been observed to assume the quiet plumage of the hen-bird; and
+the _Falco albidus_ returned to the dress of an earlier age.[384] Mr.
+Thomson, the superintendent of the Knowsley menagerie, informed me that he
+had often observed analogous facts. The horns of a male deer (_Cervus
+Canadensis_) during the voyage from America were badly developed; but
+subsequently in Paris perfect horns were produced.
+
+When conception takes place under confinement, the young are often born
+dead, or die soon, or are ill-formed. This frequently occurs in the
+Zoological Gardens, and, according to Rengger, with native animals confined
+in Paraguay. The mother's milk often fails. We may also attribute to the
+disturbance of the sexual functions the frequent occurrence of that
+monstrous instinct which leads the mother to devour her own offspring,--a
+mysterious case of perversion, as it at first appears.
+
+Sufficient evidence has now been advanced to prove that animals when first
+confined are eminently liable to suffer in their reproductive systems. We
+feel at first naturally inclined to attribute the result to loss of health,
+or at least to loss of vigour; but this view can hardly be admitted when we
+reflect how healthy, long-lived, and vigorous many animals are under {159}
+captivity, such as parrots, and hawks when used for hawking, chetahs when
+used for hunting, and elephants. The reproductive organs themselves are not
+diseased; and the diseases, from which animals in menageries usually
+perish, are not those which in any way affect their fertility. No domestic
+animal is more subject too disease than the sheep, yet it is remarkably
+prolific. The failure of animals to breed under confinement has been
+sometimes attributed exclusively to a failure in their sexual instincts:
+this may occasionally come into play, but there is no obvious reason why
+this instinct should be especially liable to be affected with perfectly
+tamed animals, except indeed indirectly through the reproductive system
+itself being disturbed. Moreover, numerous cases have been given of various
+animals which couple freely under confinement, but never conceive; or, if
+they conceive and produce young, these are fewer in number than is natural
+to the species. In the vegetable kingdom instinct of course can play no
+part; and we shall presently see that plants when removed from their
+natural conditions are affected in nearly the same manner as animals.
+Change of climate cannot be the cause of the loss of fertility, for, whilst
+many animals imported into Europe from extremely different climates breed
+freely, many others when confined in their native land are completely
+sterile. Change of food cannot be the chief cause; for ostriches, ducks,
+and many other animals, which must have undergone a great change in this
+respect, breed freely. Carnivorous birds when confined are extremely
+sterile; whilst most carnivorous mammals, except plantigrades, are
+moderately fertile. Nor can the amount of food be the cause; for a
+sufficient supply will certainly be given to valuable animals; and there is
+no reason to suppose that much more food would be given to them, than to
+our choice domestic productions which retain their full fertility. Lastly,
+we may infer from the case of the elephant, chetah, various hawks, and of
+many animals which are allowed to lead an almost free life in their native
+land, that want of exercise is not the sole cause.
+
+It would appear that any change in the habits of life, whatever these
+habits may be, if great enough, tends to affect in an inexplicable manner
+the powers of reproduction. The result {160} depends more on the
+constitution of the species than on the nature of the change; for certain
+whole groups are affected more than others; but exceptions always occur,
+for some species in the most fertile groups refuse to breed, and some in
+the most sterile groups breed freely. Those animals which usually breed
+freely under confinement, rarely breed, as I was assured, in the Zoological
+Gardens, within a year or two after their first importation. When an animal
+which is generally sterile under confinement happens to breed, the young
+apparently do not inherit this power; for had this been the case, various
+quadrupeds and birds, which are valuable for exhibition, would have become
+common. Dr. Broca even affirms[385] that many animals in the Jardin des
+Plantes, after having produced young for three or four successive
+generations, become sterile; but this may be the result of too close
+interbreeding. It is a remarkable circumstance that many mammals and birds
+have produced hybrids under confinement quite as readily as, or even more
+readily than, they have procreated their own kind. Of this fact many
+instances have been given;[386] and we are thus reminded of those plants
+which when cultivated refuse to be fertilised by their own pollen, but can
+easily be fertilised by that of a distinct species. Finally, we must
+conclude, limited as the conclusion is, that changed conditions of life
+have an especial power of acting injuriously on the reproductive system.
+The whole case is quite peculiar, for these organs, though not diseased,
+are thus rendered incapable of performing their proper functions, or
+perform them imperfectly.
+
+    _Sterility of Domesticated Animals from changed conditions._--With
+    respect to domesticated animals, as their domestication mainly depends
+    on the accident of their breeding freely under captivity, we ought not
+    to expect that their reproductive system would be affected by any
+    moderate degree of change. Those orders of quadrupeds and birds, of
+    which the wild species breed most readily in our menageries, have
+    afforded us the greatest number of domesticated productions. Savages in
+    most parts of the world are fond of taming animals;[387] and if any of
+    these regularly produced {161} young, and were at the same time useful,
+    they would be at once domesticated. If, when their masters migrated
+    into other countries, they were in addition found capable of
+    withstanding various climates, they would be still more valuable; and
+    it appears that the animals which breed readily in captivity can
+    generally withstand different climates. Some few domesticated animals,
+    such as the reindeer and camel, offer an exception to this rule. Many
+    of our domesticated animals can bear with undiminished fertility the
+    most unnatural conditions; for instance, rabbits, guinea-pigs, and
+    ferrets breed in miserably confined hutches. Few European dogs of any
+    kind withstand without degeneration the climate of India; but as long
+    as they survive, they retain, as I hear from Mr. Falconer, their
+    fertility; so it is, according to Dr. Daniell, with English dogs taken
+    to Sierra Leone. The fowl, a native of the hot jungles of India,
+    becomes more fertile than its parent-stock in every quarter of the
+    world, until we advance as far north as Greenland and Northern Siberia,
+    where this bird will not breed. Both fowls and pigeons, which I
+    received during the autumn direct from Sierra Leone, were at once ready
+    to couple.[388] I have, also, seen pigeons breeding as freely as the
+    common kinds within a year after their importation from the Upper Nile.
+    The guinea-fowl, an aboriginal of the hot and dry deserts of Africa,
+    whilst living under our damp and cool climate, produces a large supply
+    of eggs.
+
+    Nevertheless, our domesticated animals under new conditions
+    occasionally show signs of lessened fertility. Roulin asserts that in
+    the hot valleys of the equatorial Cordillera sheep are not fully
+    fecund;[389] and according to Lord Somerville,[390] the merino-sheep
+    which he imported from Spain were not at first perfectly fertile. It is
+    said[391] that mares brought up on dry food in the stable, and turned
+    out to grass, do not at first breed. The peahen, as we have seen, is
+    said not to lay so many eggs in England as in India. It was long before
+    the canary-bird was fully fertile, and even now first-rate breeding
+    birds are not common.[392] In the hot and dry province of Delhi, the
+    eggs of the turkey, as I hear from Dr. Falconer, though placed under a
+    hen, are extremely liable to fail. According to Roulin, geese taken
+    within a recent period to the lofty plateau of Bogota, at first laid
+    seldom, and then only a few eggs; of these scarcely a fourth were
+    hatched, and half the young birds died: in the second generation they
+    were more fertile; and when Roulin wrote they were becoming as {162}
+    fertile as our geese in Europe. In the Philippine Archipelago the
+    goose, it is asserted, will not breed or even lay eggs.[393] A more
+    curious case is that of the fowl, which, according to Roulin, when
+    first introduced would not breed at Cusco in Bolivia, but subsequently
+    became quite fertile; and the English Game fowl, lately introduced, had
+    not as yet arrived a its full fertility, for to raise two or three
+    chickens from a nest of eggs was thought fortunate. In Europe close
+    confinement has a marked effect on the fertility of the fowl: it has
+    been found in France that with fowls allowed considerable freedom only
+    twenty per cent. of the eggs failed; when allowed less freedom forty
+    per cent. failed; and in close confinement sixty out of the hundred
+    were not hatched.[394] So we see that unnatural and changed conditions
+    of life produce some effect on the fertility of our most thoroughly
+    domesticated animals, in the same manner, though in a far less degree,
+    as with captive wild animals.
+
+    It is by no means rare to find certain males and females which will not
+    breed together, though both are known to be perfectly fertile with
+    other males and females. We have no reason to suppose that this is
+    caused by these animals having been subjected to any change in their
+    habits of life; therefore such cases are hardly related to our present
+    subject. The cause apparently lies in an innate sexual incompatibility
+    of the pair which are matched. Several instances have been communicated
+    to me by Mr. W. C. Spooner (well known for his essay on
+    Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and othe
+    breeders, and especially by Mr. Waring of Chelsfield, in relation to
+    horses, cattle, pigs, foxhounds, other dogs, and pigeons.[395] In these
+    cases, females, which either previously or subsequently were proved to
+    be fertile, failed to breed with certain males, with whom it was
+    particularly desired to match them. A change in the constitution of the
+    female may sometimes have occurred before she was put to the second
+    male; but in other cases this explanation is hardly tenable, for a
+    female, known not to be barren, has been unsuccessfully paired seven or
+    eight times with the same male likewise known to be perfectly fertile.
+    With cart-mares, which sometimes will not breed with stallions of pure
+    blood, but subsequently have bred with cart-stallions, Mr. Spooner is
+    inclined to attribute the failure to the lesser sexual power of the
+    race-horse. But I have heard from the greatest breeder of race-horses
+    at the present day, through Mr. Waring, that "it frequently occurs with
+    a mare to be put several times during one or two seasons to a
+    particular stallion of acknowledged power, and yet prove barren; the
+    mare afterwards breeding at once with some other horse." These facts
+    are worth recording, as they show, like so many previous facts, on what
+    slight constitutional differences the fertility of an animal often
+    depends.
+
+{163}
+
+_Sterility of Plants from changed Conditions of Life, and from other
+causes._
+
+In the vegetable kingdom cases of sterility frequently occur, analogous
+with those previously given in the animal kingdom. But the subject is
+obscured by several circumstances, presently to be discussed, namely, the
+contabescence of the anthers, as Gaertner has named a certain
+affection--monstrosities--doubleness of the flower--much-enlarged
+fruit--and long-continued or excessive propagation by buds.
+
+    It is notorious that many plants in our gardens and hot-houses, though
+    preserved in the most perfect health, rarely or never produce seed. I
+    do not allude to plants which run to leaves, from being kept too damp,
+    or too warm, or too much manured; for these do not produce the
+    reproductive individual or flower, and the case may be wholly
+    different. Nor do I allude to fruit not ripening from want of heat, or
+    rotting from too much moisture. But many exotic plants, with their
+    ovules and pollen appearing perfectly sound, will not set any seed. The
+    sterility in many cases, as I know from my own observation, is simply
+    due to the absence of the proper insects for carrying the pollen to the
+    stigma. But after excluding the several cases just specified, there are
+    many plants in which the reproductive system has been seriously
+    affected by the altered conditions of life to which they have been
+    subjected.
+
+    It would be tedious to enter on many details. Linnaeus long ago
+    observed[396] that Alpine plants, although naturally laded with seed,
+    produce either few or none when cultivated in gardens. But exceptions
+    often occur: the _Draba sylvestris_, one of our most thoroughly Alpine
+    plants, multiplies itself by seed in Mr. H. C. Watson's garden, near
+    London; and Kerner, who has particularly attended to the cultivation of
+    Alpine plants, found that various kinds, when cultivated, spontaneously
+    sowed themselves.[397] Many plants which naturally grow in peat-earth
+    are entirely sterile in our gardens. I have noticed the same fact with
+    several liliaceous plants, which nevertheless grew vigorously.
+
+    Too much manure renders some kinds utterly sterile, as I have myself
+    observed. The tendency to sterility from this cause runs in families;
+    thus, according to Gaertner,[398] it is hardly possible to give too
+    much manure to most Gramineae, Cruciferae, and Leguminosae, whilst
+    succulent and bulbous-rooted plants are easily affected. Extreme
+    poverty of soil is less {164} apt to induce sterility; but dwarfed
+    plants of _Trifolium minus_ and _repens_, growing on a lawn often mown
+    and never manured, did not produce any seed. The temperature of the
+    soil, and the season at which plants are watered, often have a marked
+    effect on their fertility, as was observed by Koelreuter in the case of
+    Mirabilis.[399] Mr. Scott in the Botanic Gardens of Edinburgh observed
+    that _Oncidium divaricatum_ would not set seed when grown in a basket
+    in which it throve, but was capable of fertilisation in a pot where it
+    was a little damper. _Pelargonium fulgidum_, for many years after its
+    introduction, seeded freely; it then became sterile; now it is
+    fertile[400] if kept in a dry stove during the winter. Other varieties
+    of pelargonium are sterile and others fertile without our being able to
+    assign any cause. Very slight changes in the position of a plant,
+    whether planted on a bank or at its base, sometimes make all the
+    difference in its producing seed. Temperature apparently has a much
+    more powerful influence on the fertility of plants than on that of
+    animals. Nevertheless it is wonderful what changes some few plants will
+    withstand with undiminished fertility: thus the _Zephyranthes candida_,
+    a native of the moderately warm banks of the Plata, sows itself in the
+    hot dry country near Lima, and in Yorkshire resists the severest
+    frosts, and I have seen seeds gathered from pods which had been covered
+    with snow during three weeks.[401] _Berberis Wallichii_, from the hot
+    Khasia range in India, is uninjured by our sharpest frosts, and ripens
+    its fruit under our cool summers. Nevertheless I presume we must
+    attribute to change of climate the sterility of many foreign plants;
+    thus the Persian and Chinese lilacs (_Syringa Persica_ and
+    _Chinensis_), though perfectly hardly, never here produce a seed; the
+    common lilac (_S. vulgaris_) seeds with us moderately well, but in
+    parts of Germany the capsules never contain seed.[402]
+
+    Some of the cases, given in the last chapter, of self-impotent plants,
+    which are fertile both on the male and female side when united with
+    distinct individuals or species, might have been here introduced; for
+    as this peculiar form of sterility generally occurs with exotic plants
+    or with endemic plants cultivated in pots, and as it disappeared in the
+    _Passiflora alata_ when grafted, we may conclude that in these cases it
+    is the result of the treatment to which the plants or their parents
+    have been exposed.
+
+    The liability of plants to be affected in their fertility by slightly
+    changed conditions is the more remarkable, as the pollen when once in
+    process of formation is not easily injured; a plant may be
+    transplanted, or a branch with flower-buds be cut off and placed in
+    water, and the pollen will be matured. Pollen, also, when once mature,
+    may be kept for weeks or even months.[403] The female organs are more
+    sensitive, for Gaertner[404] found that dicotyledonous plants, when
+    carefully removed so that they did not in the least flag, could seldom
+    be fertilised; this occurred even with potted {165} plants if the roots
+    had grown out of the hole at the bottom. In some few cases, however, as
+    with Digitalis, transplantation did not prevent fertilisation; and
+    according to the testimony of Mawz, _Brassica rapa_, when pulled up by
+    its roots and placed in water, ripened its seed. Flower-stems of
+    several monocotyledonous plants when cut off and placed in water
+    likewise produce seed. But in these cases I presume that the flowers
+    had been already fertilised, for Herbert[405] found with the Crocus
+    that the plants might be removed or mutilated after the act of
+    fertilisation, and would still perfect their seeds; but that, if
+    transplanted before being fertilised, the application of pollen was
+    powerless.
+
+    Plants which have been long cultivated can generally endure with
+    undiminished fertility various and great changes; but not in most cases
+    so great a change of climate as domesticated animals. It is remarkable
+    that many plants under these circumstances are so much affected that
+    the proportions and the nature of their chemical ingredients are
+    modified, yet their fertility is unimpaired. Thus, as Dr. Falconer
+    informs me, there is a great difference in the character of the fibre
+    in hemp, in the quantity of oil in the seed of the Linum, in the
+    proportion of narcotin to morphine in the poppy, in gluten to starch in
+    wheat, when these plants are cultivated on the plains and on the
+    mountains of India; nevertheless, they all remain fully fertile.
+
+    _Contabescence._--Gaertner has designated by this term a peculiar
+    condition of the anthers in certain plants, in which they are
+    shrivelled, or become brown and tough, and contain no good pollen. When
+    in this state they exactly resemble the anthers of the most sterile
+    hybrids. Gaertner,[406] in his discussion on this subject, has shown
+    that plants of many orders are occasionally thus affected; but the
+    Caryophyllaceae and Liliaceae suffer most, and to these orders, I
+    think, the Ericaceae may be added. Contabescence varies in degree, but
+    on the same plant all the flowers are generally affected to nearly the
+    same extent. The anthers are affected at a very early period in the
+    flower-bud, and remain in the same state (with one recorded exception)
+    during the life of the plant. The affection cannot be cured by any
+    change of treatment, and is propagated by layers, cuttings, &c., and
+    perhaps even by seed. In contabescent plants the female organs are
+    seldom affected, or merely become precocious in their development. The
+    cause of this affection is doubtful, and is different in different
+    cases. Until I read Gaertner's discussion I attributed it, as
+    apparently did Herbert, to the unnatural treatment of the plants; but
+    its permanence under changed conditions, and the female organs not
+    being affected, seem incompatible with this view. The fact of several
+    endemic plants becoming contabescent in our gardens seems, at first
+    sight, equally incompatible with this view; but Koelreuter believes
+    that this is the result of their transplantation. The contabescent
+    plants of Dianthus and Verbascum, found wild by Wiegmann, grew on a dry
+    and sterile bank. The fact that exotic {166} plants are eminently
+    liable to this affection also seems to show that it is in some manner
+    caused by their unnatural treatment. In some instances, as with Silene,
+    Gaertner's view seems the most probable, namely, that it is caused by
+    an inherent tendency in the species to become dioecious. I can add
+    another cause, namely, the illegitimate unions of reciprocally
+    dimorphic or trimorphic plants, for I have observed seedlings of three
+    species of Primula and of _Lythrum salicaria_, which had been raised
+    from plants illegitimately fertilised by their own-form pollen, with
+    some or all their anthers in a contabescent state. There is perhaps an
+    additional cause, namely, self-fertilisation; for many plants of
+    Dianthus and Lobelia, which had been raised from self-fertilised seeds,
+    had their anthers in this state; but these instances are not
+    conclusive, as both genera are liable from other causes to this
+    affection.
+
+    Cases of an opposite nature likewise occur, namely, plants with the
+    female organs struck with sterility, whilst the male organs remain
+    perfect. _Dianthus Japonicus_, a Passiflora, and Nicotiana, have been
+    described by Gaertner[407] as being in this unusual condition.
+
+    _Monstrosities as a cause of Sterility._--Great deviations of
+    structure, even when the reproductive organs themselves are not
+    seriously affected, sometimes cause plants to become sterile. But in
+    other cases plants may become monstrous to an extreme degree and yet
+    retain their full fertility. Gallesio, who certainly had great
+    experience,[408] often attributes sterility to this cause; but it may
+    be suspected that in some of his cases sterility was the cause, and not
+    the result, of the monstrous growths. The curious St. Valery apple,
+    although it bears fruit, rarely produces seed. The wonderfully
+    anomalous flowers of _Begonia frigida_, formerly described, though they
+    appear fit for fructification, are sterile.[409] Species of Primulae,
+    in which the calyx is brightly coloured, are said[410] to be often
+    sterile, though I have known them to be fertile. On the other hand,
+    Verlot gives several cases of proliferous flowers which can be
+    propagated by seed. This was the case with a poppy, which had become
+    monopetalous by the union of its petals.[411] Another extraordinary
+    poppy, with the stamens replaced by numerous small supplementary
+    capsules, likewise reproduces itself by seed. This has also occurred
+    with a plant of _Saxifraga geum_, in which a series of adventitious
+    carpels, bearing ovules on their margins, had been developed between
+    the stamens and the normal carpels.[412] Lastly, with respect to
+    peloric flowers, which depart wonderfully from the natural
+    structure,--those of _Linaria vulgaris_ seem generally to be more or
+    less sterile, whilst those before described of _Antirrhinum majus_,
+    when artificially fertilised with their own pollen, are perfectly {167}
+    fertile, though sterile when left to themselves, for bees are unable to
+    crawl into the narrow tubular flower. The peloric flowers of _Corydalis
+    solida_, according to Godron,[413] are barren; whilst those of Gloxinia
+    are well known to yield plenty of seed. In our greenhouse Pelargoniums,
+    the central flower of the truss is often peloric, and Mr. Masters
+    informs me that he tried in vain during several years to get seed from
+    these flowers. I likewise made many vain attempts, but sometimes
+    succeeded in fertilising them with pollen from a normal flower of
+    another variety; and conversely I several times fertilised ordinary
+    flowers with peloric pollen. Only once I succeeded in raising a plant
+    from a peloric flower fertilised by pollen from a peloric flower borne
+    by another variety; but the plant, it may be added, presented nothing
+    particular in its structure. Hence we may conclude that no general rule
+    can be laid down; but any great deviation from the normal structure,
+    even when the reproductive organs themselves are not seriously
+    affected, certainly often leads to sexual impotence.
+
+    _Double Flowers._--When the stamens are converted into petals, the
+    plant becomes on the male side sterile; when both stamens and pistils
+    are thus changed, the plant becomes completely barren. Symmetrical
+    flowers having numerous stamens and petals are the most liable to
+    become double, as perhaps follows from all multiple organs being the
+    most subject to variability. But flowers furnished with only a few
+    stamens, and others which are asymmetrical in structure, sometimes
+    become double, as we see with the double gorse or Ulex, Petunia, and
+    Antirrhinum. The Compositae bear what are called double flowers by the
+    abnormal development of the corolla of their central florets.
+    Doubleness is sometimes connected with prolification,[414] or the
+    continued growth of the axis of the flower. Doubleness is strongly
+    inherited. No one has produced, as Lindley remarks,[415] double flowers
+    by promoting the perfect health of the plant. On the contrary,
+    unnatural conditions of life favour their production. There is some
+    reason to believe that seeds kept during many years, and seeds believed
+    to be imperfectly fertilised, yield double flowers more freely than
+    fresh and perfectly fertilised seed.[416] Long-continued cultivation in
+    rich soil seems to be the commonest exciting cause. A double narcissus
+    and a double _Anthemis nobilis_, transplanted into very poor soil, have
+    been observed to become single;[417] and I have seen a completely
+    double white primrose rendered permanently single by being divided and
+    transplanted whilst in full flower. It has been observed by Professor
+    Morren that doubleness of the flowers and variegation of the leaves are
+    antagonistic states; but so many exceptions to the rule have lately
+    been recorded,[418] that, though general, it cannot be looked at as
+    invariable. {168} Variegation seems generally to result from a feeble
+    or atrophied condition of the plant, and a large proportion of the
+    seedlings raised from parents both of which are variegated usually
+    perish at an early age; hence we may perhaps infer that doubleness,
+    which is the antagonistic state, commonly arises from a plethoric
+    condition. On the other hand, extremely poor soil sometimes, though
+    rarely, appears to cause doubleness: I formerly described[419] some
+    completely double, bud-like, flowers produced in large numbers by
+    stunted wild plants of _Gentiana amarella_ growing on a poor chalky
+    bank. I have also noticed a distinct tendency to doubleness in the
+    flowers of a Ranunculus, Horse-chesnut, and Bladder-nut (_Ranunculus
+    repens_, _Aesculus pavia_, and _Staphylea_), growing under very
+    unfavourable conditions. Professor Lehman[420] found several wild
+    plants growing near a hot spring with double flowers. With respect to
+    the cause of doubleness, which arises, as we see, under widely
+    different circumstances, I shall presently attempt to show that the
+    most probable view is that unnatural conditions first give a tendency
+    to sterility, and that then, on the principle of compensation, as the
+    reproductive organs do not perform their proper functions, they either
+    become developed into petals, or additional petals are formed. This
+    view has lately been supported by Mr. Laxton,[421] who advances the
+    case of some common peas, which, after long-continued heavy rain,
+    flowered a second time, and produced double flowers.
+
+    _Seedless Fruit._--Many of our most valuable fruits, although
+    consisting in a homological sense of widely different organs, are
+    either quite sterile, or produce extremely few seeds. This is
+    notoriously the case with our best pears, grapes, and figs, with the
+    pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms, and
+    some members of the orange-tribe. Poorer varieties of these same fruits
+    either habitually or occasionally yield seed.[422] Most horticulturists
+    look at the great size and anomalous development of the fruit as the
+    cause, and sterility as the result; but the opposite view, as we shall
+    presently see, is more probable.
+
+    _Sterility from the excessive development of the Organs of Growth or
+    Vegetation._--Plants which from any cause grow too luxuriantly, and
+    produce leaves, stems, runners, suckers, tubers, bulbs, &c., in excess,
+    sometimes do not flower, or if they flower do not yield seed. To make
+    European vegetables under the hot climate of India yield seed, it is
+    necessary to check their growth; and, when one-third grown, they are
+    taken up, and their stems and {169} tap-roots are cut or
+    mutilated.[423] So it is with hybrids; for instance, Prof. Lecoq[424]
+    had three plants of Mirabilis, which, though they grew luxuriantly and
+    flowered, were quite sterile; but after beating one with a stick until
+    a few branches alone were left, these at once yielded good seed. The
+    sugar-cane, which grows vigorously and produces a large supply of
+    succulent stems, never, according to various observers, bears seed in
+    the West Indies, Malaga, India, Cochin China, or the Malay
+    Archipelago.[425] Plants which produce a large number of tubers are apt
+    to be sterile, as occurs, to a certain extent, with the common potato;
+    and Mr. Fortune informs me that the sweet potato (_Convolvulus
+    batatas_) in China never, as far as he has seen, yields seed. Dr. Royle
+    remarks[426] that in India the _Agave vivipara_, when grown in rich
+    soil, invariably produces bulbs, but no seeds; whilst a poor soil and
+    dry climate leads to an opposite result. In China, according to Mr.
+    Fortune, an extraordinary number of little bulbs are developed in the
+    axils of the leaves of the yam, and this plant does not bear seed.
+    Whether in these cases, as in those of double flowers and seedless
+    fruit, sexual sterility from changed conditions of life is the primary
+    cause which leads to the excessive development of the organs of
+    vegetation, is doubtful; though some evidence might be advanced in
+    favour of this view. It is perhaps a more probable view that plants
+    which propagate themselves largely by one method, namely by buds, have
+    not sufficient vital power or organised matter for the other method of
+    sexual generation.
+
+    Several distinguished botanists and good practical judges believe that
+    long-continued propagation by cuttings, runners, tubers, bulbs, &c.,
+    independently of any excessive development of these parts, is the cause
+    of many plants failing to produce flowers and of others failing to
+    produce fertile flowers,--it is as if they had lost the habit of sexual
+    generation.[427] That many plants when thus propagated are sterile
+    there can be no doubt, but whether the long continuance of this form of
+    propagation is the actual cause of their sterility, I will not venture,
+    from the want of sufficient evidence, to express an opinion.
+
+    That plants may be propagated for long periods by buds, without the aid
+    of sexual generation, we may safely infer from this being the case with
+    many plants which must have long survived in a state of nature. As I
+    have had occasion before to allude to this subject, I will here give
+    such cases as I have collected. Many alpine plants ascend mountains
+    beyond the height at which they can produce seed.[428] Certain species
+    of {170} Poa and Festuca, when growing on mountain-pastures, propagate
+    themselves, as I hear from Mr. Bentham, almost exclusively by bulblets.
+    Kalm gives a more curious instance[429] of several American trees,
+    which grow so plentifully in marshes or in thick woods, that they are
+    certainly well adapted for these stations, yet scarcely ever produce
+    seeds; but when accidentally growing on the outside of the marsh or
+    wood, are loaded with seed. The common ivy is found in Northern Sweden
+    and Russia, but flowers and fruits only in the southern provinces. The
+    _Acorus calamus_ extends over a large portion of the globe, but so
+    rarely perfects its fruit that this has been seen but by few
+    botanists.[430] The _Hypericum calycinum_, which propagates itself so
+    freely in our shrubberies by rhizomas and is naturalised in Ireland,
+    blossoms profusely, but sets no seed; nor did it set any when
+    fertilised in my garden by pollen from plants growing at a distance.
+    The _Lysimachia nummularia_, which is furnished with long runners, so
+    seldom produces seed-capsules, that Prof. Decaisne,[431] who has
+    especially attended to this plant, has never seen it in fruit. The
+    _Carex rigida_ often fails to perfect its seed in Scotland, Lapland,
+    Greenland, Germany, and New Hampshire in the United States.[432] The
+    periwinkle (_Vinca minor_), which spreads largely by runners, is said
+    scarcely ever to produce fruit in England;[433] but this plant requires
+    insect-aid for its fertilisation, and the proper insects may be absent
+    or rare. The _Jussiaea grandiflora_ has become naturalised in Southern
+    France, and has spread by its rhizomas so extensively as to impede the
+    navigation of the waters, but never produces fertile seed.[434] The
+    horse-radish (_Cochlearia armoracia_) spreads pertinaciously and is
+    naturalised in various parts of Europe; though it bears flowers, these
+    rarely produce capsules: Professor Caspary also informs me that he has
+    watched this plant since 1851, but has never seen its fruit; nor is
+    this surprising, as he finds scarcely a grain of good pollen. The
+    common little _Ranunculus ficaria_ rarely, and some say never, bears
+    seed in England, France, or Switzerland; but in 1863 I observed seeds
+    on several plants growing near my house. According to M. Chatin, there
+    are two forms of this Ranunculus; and it is the bulbiferous form which
+    does not yield seed from producing no pollen.[435] Other cases {171}
+    analogous with the foregoing could be given; for instance, some kinds
+    of mosses and lichens have never been seen to fructify in France.
+
+    Some of these endemic and naturalised plants are probably rendered
+    sterile from excessive multiplication by buds, and their consequent
+    incapacity to produce and nourish seed. But the sterility of others
+    more probably depends on the peculiar conditions under which they live,
+    as in the case of the ivy in the northern parts of Europe, and of the
+    trees in the swamps of the United States; yet these plants must be in
+    some respects eminently well adapted for the stations which they
+    occupy, for they hold their places against a host of competitors.
+
+Finally, when we reflect on the sterility which accompanies the doubling of
+flowers,--the excessive development of fruit,--and a great increase in the
+organs of vegetation, we must bear in mind that the whole effect has seldom
+been caused at once. An incipient tendency is observed, and continued
+selection completes the work, as is known to be the case with our double
+flowers and best fruits. The view which seems the most probable, and which
+connects together all the foregoing facts and brings them within our
+present subject, is, that changed and unnatural conditions of life first
+give a tendency to sterility; and in consequence of this, the organs of
+reproduction being no longer able fully to perform their proper functions,
+a supply of organised matter, not required for the development of the seed,
+flows either into these same organs and renders them foliaceous, or into
+the fruit, stems, tubers, &c., increasing their size and succulency. But I
+am far from wishing to deny that there exists, independently of any
+incipient sterility, an antagonism between the two forms of reproduction,
+namely, by seed and by buds, when either is carried to an extreme degree.
+That incipient sterility plays an important part in the doubling of
+flowers, and in the other cases just specified, I infer chiefly from the
+following facts. When fertility is lost from a wholly different cause,
+namely, from hybridism, there is a strong tendency, as Gaertner[436]
+affirms, for flowers to become double, and this tendency is inherited.
+Moreover it is notorious that with hybrids the male organs become sterile
+before the female organs, and with double flowers the stamens first become
+{172} foliaceous. This latter fact is well shown by the male flowers of
+dioecious plants, which, according to Gallesio,[437] first become double.
+Again, Gaertner[438] often insists that the flowers of even utterly sterile
+hybrids, which do not produce any seed, generally yield perfect capsules or
+fruit,--a fact which has likewise been repeatedly observed by Naudin with
+the Cucurbitaceae; so that the production of fruit by plants rendered
+sterile through any other and distinct cause is intelligible. Koelreuter
+has also expressed his unbounded astonishment at the size and development
+of the tubers in certain hybrids; and all experimentalists[439] have
+remarked on the strong tendency in hybrids to increase by roots, runners,
+and suckers. Seeing that hybrid plants, which from their nature are more or
+less sterile, thus tend to produce double flowers; that they have the parts
+including the seed, that is the fruit, perfectly developed, even when
+containing no seed; that they sometimes yield gigantic roots; that they
+almost invariably tend to increase largely by suckers and other such
+means;--seeing this, and knowing, from the many facts given in the earlier
+parts of this chapter, that almost all organic beings when exposed to
+unnatural conditions tend to become more or less sterile, it seems much the
+most probable view that with cultivated plants sterility is the exciting
+cause, and double flowers, rich seedless fruit, and in some cases
+largely-developed organs of vegetation, &c., are the indirect
+results--these results having been in most cases largely increased through
+continued selection by man.
+
+       *       *       *       *       *
+
+
+{173}
+
+CHAPTER XIX.
+
+SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.
+
+    ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON
+    FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED
+    CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON
+    THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND
+    VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON
+    HYBRIDISM BY THE ILLEGITIMATE PROGENY OF DIMORPHIC AND TRIMORPHIC
+    PLANTS--STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE
+    REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS
+    WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS
+    BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND
+    CROSSED VARIETIES--CONCLUSION.
+
+It was shown in the fifteenth chapter that when individuals of the same
+variety, or even of a distinct variety, are allowed freely to intercross,
+uniformity of character is ultimately acquired. Some few characters,
+however, are incapable of fusion, but these are unimportant, as they are
+almost always of a semi-monstrous nature, and have suddenly appeared.
+Hence, to preserve our domesticated breeds true, or to improve them by
+methodical selection, it is obviously necessary that they should be kept
+separate. Nevertheless, through unconscious selection, a whole body of
+individuals may be slowly modified, as we shall see in a future chapter,
+without separating them into distinct lots. Domestic races have often been
+intentionally modified by one or two crosses, made with some allied race,
+and occasionally even by repeated crosses with very distinct races; but in
+almost all such cases, long-continued and careful selection has been
+absolutely necessary, owing to the excessive variability of the crossed
+offspring, due to the principle of reversion. In a few instances, however,
+mongrels have retained a uniform character from their first production.
+
+When two varieties are allowed to cross freely, and one is {174} much more
+numerous than the other, the former will ultimately absorb the latter.
+Should both varieties exist in nearly equal numbers, it is probable that a
+considerable period would elapse before the acquirement of a uniform
+character; and the character ultimately acquired would largely depend on
+prepotency of transmission, and on the conditions of life; for the nature
+of these conditions would generally favour one variety more than another,
+so that a kind of natural selection would come into play. Unless the
+crossed offspring were slaughtered by man without the least discrimination,
+some degree of unmethodical selection would likewise come into action. From
+these several considerations we may infer, that when two or more closely
+allied species first came into the possession of the same tribe, their
+crossing will not have influenced, in so great a degree as has often been
+supposed, the character of the offspring in future times; although in some
+cases it probably has had a considerable effect.
+
+Domestication, as a general rule, increases the prolificness of animals and
+plants. It eliminates the tendency to sterility which is common to species
+when first taken from a state of nature and crossed. On this latter head we
+have no direct evidence; but as our races of dogs, cattle, pigs, &c., are
+almost certainly descended from aboriginally distinct stocks, and as these
+races are now fully fertile together, or at least incomparably more fertile
+than most species when crossed, we may with much confidence accept this
+conclusion.
+
+Abundant evidence has been given that crossing adds to the size, vigour,
+and fertility of the offspring. This holds good when there has been no
+previous close interbreeding. It applies to the individuals of the same
+variety but belonging to different families, to distinct varieties,
+sub-species, and partially even to species. In the latter case, though size
+is often gained, fertility is lost; but the increased size, vigour, and
+hardiness of many hybrids cannot be accounted for solely on the principle
+of compensation from the inaction of the reproductive system. Certain
+plants, both of pure and hybrid origin, though perfectly healthy, have
+become self-impotent, apparently from the unnatural conditions to which
+they have been exposed; and such plants, as well as others in their normal
+state, can be stimulated to {175} fertility only by crossing them with
+other individuals of the same species or even of a distinct species.
+
+On the other hand, long-continued close interbreeding between the nearest
+relations diminishes the constitutional vigour, size, and fertility of the
+offspring; and occasionally leads to malformations, but not necessarily to
+general deterioration of form or structure. This failure of fertility shows
+that the evil results of interbreeding are independent of the augmentation
+of morbid tendencies common to both parents, though this augmentation no
+doubt is often highly injurious. Our belief that evil follows from close
+interbreeding rests to a large extent on the experience of practical
+breeders, especially of those who have reared many animals of the kinds
+which can be propagated quickly; but it likewise rests on several carefully
+recorded experiments. With some animals close interbreeding may be carried
+on for a long period with impunity by the selection of the most vigorous
+and healthy individuals; but sooner or later evil follows. The evil,
+however, comes on so slowly and gradually that it easily escapes
+observation, but can be recognised by the almost instantaneous manner in
+which size, constitutional vigour, and fertility are regained when animals
+that have long been interbred are crossed with a distinct family.
+
+These two great classes of facts, namely, the good derived from crossing,
+and the evil from close interbreeding, with the consideration of the
+innumerable adaptations throughout nature for compelling, or favouring, or
+at least permitting, the occasional union of distinct individuals, taken
+together, lead to the conclusion that it is a law of nature that organic
+beings shall not fertilise themselves for perpetuity. This law was first
+plainly hinted at in 1799, with respect to plants, by Andrew Knight,[440]
+and, not long afterwards, that sagacious observer Koelreuter, after showing
+how well the Malvaceae are adapted for {176} crossing, asks, "an id aliquid
+in recessu habeat, quod hujuscemodi flores nunquam proprio suo pulvere, sed
+semper eo aliarum suae speciei impregnentur, merito quaeritur? Certe natura
+nil facit frustra." Although we may demur to Koelreuter's saying that
+nature does nothing in vain, seeing how many organic beings retain
+rudimentary and useless organs, yet undoubtedly the argument from the
+innumerable contrivances, which favour the crossing of distinct individuals
+of the same species, is of the greatest weight. The most important result
+of this law is that it leads to uniformity of character in the individuals
+of the same species. In the case of certain hermaphrodites, which probably
+intercross only at long intervals of time, and with unisexual animals
+inhabiting somewhat separated localities, which can only occasionally come
+into contact and pair, the greater vigour and fertility of the crossed
+offspring will ultimately prevail in giving uniformity of character to the
+individuals of the same species. But when we go beyond the limits of the
+same species, free intercrossing is barred by the law of sterility.
+
+In searching for facts which might throw light on the cause of the good
+effects from crossing, and of the evil effects from close interbreeding, we
+have seen that, on the one hand, it is a widely prevalent and ancient
+belief that animals and plants profit from slight changes in their
+condition of life; and it would appear that the germ, in a somewhat
+analogous manner, is more effectually stimulated by the male element, when
+taken from a distinct individual, and therefore slightly modified in
+nature, than when taken from a male having the same identical constitution.
+On the other hand, numerous facts have been given, showing that when
+animals are first subjected to captivity, even in their native land, and
+although allowed much liberty, their reproductive functions are often
+greatly impaired or quite annulled. Some groups of animals are more
+affected than others, but with apparently capricious exceptions in every
+group. Some animals never or rarely couple: some couple freely, but never
+or rarely conceive. The secondary male characters, the maternal functions
+and instincts, are occasionally affected. With plants, when first subjected
+to cultivation, analogous facts have been observed. We probably owe our
+double flowers, rich seedless {177} fruits, and in some cases greatly
+developed tubers, &c., to incipient sterility of the above nature combined
+with a copious supply of nutriment. Animals which have long been
+domesticated, and plants which have long been cultivated, can generally
+withstand with unimpaired fertility great changes in their conditions of
+life; though both are sometimes slightly affected. With animals the
+somewhat rare capacity of breeding freely under confinement has mainly
+determined, together with their utility, the kinds which have been
+domesticated.
+
+We can in no case precisely say what is the cause of the diminished
+fertility of an animal when first captured, or of a plant when first
+cultivated; we can only infer that it is caused by a change of some kind in
+the natural conditions of life. The remarkable susceptibility of the
+reproductive system to such changes,--a susceptibility not common to any
+other organ,--apparently has an important bearing on Variability, as we
+shall see in a future chapter.
+
+It is impossible not to be struck with the double parallelism between the
+two classes of facts just alluded to. On the one hand, slight changes in
+the conditions of life, and crosses between slightly modified forms or
+varieties, are beneficial as far as prolificness and constitutional vigour
+are concerned. On the other hand, changes in the conditions greater in
+degree, or of a different nature, and crosses between forms which have been
+slowly and greatly modified by natural means,--in other words, between
+species,--are highly injurious, as far as the reproductive system is
+concerned, and in some few instances as far as constitutional vigour is
+concerned. Can this parallelism be accidental? Does it not rather indicate
+some real bond of connection? As a fire goes out unless it be stirred up,
+so the vital forces are always tending, according to Mr. Herbert Spencer,
+to a state of equilibrium, unless disturbed and renovated through the
+action of other forces.
+
+In some few cases varieties tend to keep distinct, by breeding at different
+periods, by great differences in size, or by sexual preference,--in this
+latter respect more especially resembling species in a state of nature. But
+the actual crossing of varieties, far from diminishing, generally adds to
+the fertility of both the first union and the mongrel offspring. Whether
+all {178} the most widely distinct domestic varieties are invariably quite
+fertile when crossed, we do not positively know; much time and trouble
+would be requisite for the necessary experiments, and many difficulties
+occur, such as the descent of the various races from aboriginally distinct
+species, and the doubts whether certain forms ought to be ranked as species
+or varieties. Nevertheless, the wide experience of practical breeders
+proves that the great majority of varieties, even if some should hereafter
+prove not to be indefinitely fertile _inter se_, are far more fertile when
+crossed, than the vast majority of closely allied natural species. A few
+remarkable cases have, however, been given on the authority of excellent
+observers, showing that with plants certain forms, which undoubtedly must
+be ranked as varieties, yield fewer seeds when crossed than is natural to
+the parent-species. Other varieties have had their reproductive powers so
+far modified that they are either more or less fertile than are their
+parents, when crossed with a distinct species.
+
+Nevertheless, the fact remains indisputable that domesticated varieties of
+animals and of plants, which differ greatly from each other in structure,
+but which are certainly descended from the same aboriginal species, such as
+the races of the fowl, pigeon, many vegetables, and a host of other
+productions, are extremely fertile when crossed; and this seems to make a
+broad and impassable barrier between domestic varieties and natural
+species. But, as I will now attempt to show, the distinction is not so
+great and overwhelmingly important as it at first appears.
+
+_On the Difference in Fertility between Varieties and Species when
+crossed._
+
+This work is not the proper place for fully treating the subject of
+hybridism, and I have already given in my 'Origin of Species' a moderately
+full abstract. I will here merely enumerate the general conclusions which
+may be relied on, and which bear on our present point.
+
+_Firstly_, the laws governing the production of hybrids are identical, or
+nearly identical, in the animal and vegetable kingdoms.
+
+_Secondly_, the sterility of distinct species when first united, {179} and
+that of their hybrid offspring, graduates, by an almost infinite number of
+steps, from zero, when the ovule is never impregnated and a seed-capsule is
+never formed, up to complete fertility. We can only escape the conclusion
+that some species are fully fertile when crossed, by determining to
+designate as varieties all the forms which are quite fertile. This high
+degree of fertility is, however, rare. Nevertheless plants, which have been
+exposed to unnatural conditions, sometimes become modified in so peculiar a
+manner, that they are much more fertile when crossed by a distinct species
+than when fertilised by their own pollen. Success in effecting a first
+union between two species, and the fertility of their hybrids, depends in
+an eminent degree on the conditions of life being favourable. The innate
+sterility of hybrids of the same parentage and raised from the same
+seed-capsule often differs much in degree.
+
+_Thirdly_, the degree of sterility of a first cross between two species
+does not always run strictly parallel with that of their hybrid offspring.
+Many cases are known of species which can be crossed with ease, but yield
+hybrids excessively sterile; and conversely some which can be crossed with
+great difficulty, but produce fairly fertile hybrids. This is an
+inexplicable fact, on the view that species have been specially endowed
+with mutual sterility in order to keep them distinct.
+
+_Fourthly_, the degree of sterility often differs greatly in two species
+when reciprocally crossed; for the first will readily fertilise the second;
+but the latter is incapable, after hundreds of trials, of fertilising the
+former. Hybrids produced from reciprocal crosses between the same two
+species, likewise sometimes differ in their degree of sterility. These
+cases also are utterly inexplicable on the view of sterility being a
+special endowment.
+
+_Fifthly_, the degree of sterility of first crosses and of hybrids runs, to
+a certain extent, parallel with the general or systematic affinity of the
+forms which are united. For species belonging to distinct genera can
+rarely, and those belonging to distinct families can never, be crossed. The
+parallelism, however, is far from complete; for a multitude of closely
+allied species will not unite, or unite with extreme difficulty, whilst
+other species, widely different from each other, can be crossed with
+perfect facility. Nor does the difficulty depend on ordinary {180}
+constitutional differences, for annual and perennial plants, deciduous and
+evergreen trees, plants flowering at different seasons, inhabiting
+different stations, and naturally living under the most opposite climates,
+can often be crossed with ease. The difficulty or facility apparently
+depends exclusively on the sexual constitution of the species which are
+crossed; or on their sexual elective affinity, _i. e._ _Wahlverwandtschaft_
+of Gaertner. As species rarely or never become modified in one character,
+without being at the same time modified in many, and as systematic affinity
+includes all visible resemblances and dissimilarities, any difference in
+sexual constitution between two species would naturally stand in more or
+less close relation with their systematic position.
+
+_Sixthly_, the sterility of species when first crossed, and that of
+hybrids, may possibly depend to a certain extent on distinct causes. With
+pure species the reproductive organs are in a perfect condition, whilst
+with hybrids they are often plainly deteriorated. A hybrid embryo which
+partakes of the constitution of its father and mother is exposed to
+unnatural conditions, as long as it is nourished within the womb, or egg,
+or seed of the mother-form; and as we know that unnatural conditions often
+induce sterility, the reproductive organs of the hybrid might at this early
+age be permanently affected. But this cause has no bearing on the
+infertility of first unions. The diminished number of the offspring from
+first unions may often result, as is certainly sometimes the case, from the
+premature death of most of the hybrid embryos. But we shall immediately see
+that a law of an unknown nature apparently exists, which causes the
+offspring from unions, which are infertile, to be themselves more or less
+infertile; and this at present is all that can be said.
+
+_Seventhly_, hybrids and mongrels present, with the one great exception of
+fertility, the most striking accordance in all other respects; namely, in
+the laws of their resemblance to their two parents, in their tendency to
+reversion, in their variability, and in being absorbed through repeated
+crosses by either parent-form.
+
+Since arriving at the foregoing conclusions, condensed from my former work,
+I have been led to investigate a subject which throws considerable light on
+hybridism, namely, the fertility of {181} reciprocally dimorphic and
+trimorphic plants, when illegitimately united. I have had occasion several
+times to allude to these plants, and I may here give a brief abstract[441]
+of my observations. Several plants belonging to distinct orders present two
+forms, which exist in about equal numbers, and which differ in no respect
+except in their reproductive organs; one form having a long pistil with
+short stamens, the other a short pistil with long stamens; both with
+differently sized pollen-grains. With trimorphic plants there are three
+forms likewise differing in the lengths of their pistils and stamens, in
+the size and colour of the pollen-grains, and in some other respects; and
+as in each of the three forms there are two sets of stamens, there are
+altogether six sets of stamens and three kinds of pistils. These organs are
+so proportioned in length to each other that, in any two of the forms, half
+the stamens in each stand on a level with the stigma of the third form. Now
+I have shown, and the result has been confirmed by other observers, that,
+in order to obtain full fertility with these plants, it is necessary that
+the stigma of the one form should be fertilised by pollen taken from the
+stamens of corresponding height in the other form. So that with dimorphic
+species two unions, which may be called legitimate, are fully fertile, and
+two, which may be called illegitimate, are more or less infertile. With
+trimorphic species six unions are legitimate or fully fertile, and twelve
+are illegitimate or more or less infertile.
+
+The infertility which may be observed in various dimorphic and trimorphic
+plants, when they are illegitimately fertilised, that is, by pollen taken
+from stamens not corresponding in height with the pistil, differs much in
+degree, up to absolute and utter sterility; just in the same manner as
+occurs in crossing distinct species. As the degree of sterility in the
+latter case depends in an eminent degree on the conditions of life being
+more or less favourable, so I have found it with illegitimate unions. It is
+well known that if pollen of a distinct species be placed on the stigma of
+a flower, and its own pollen be afterwards, even {182} after a considerable
+interval of time, placed on the same stigma, its action is so strongly
+prepotent that it generally annihilates the effect of the foreign pollen;
+so it is with the pollen of the several forms of the same species, for
+legitimate pollen is strongly prepotent over illegitimate pollen, when both
+are placed on the same stigma. I ascertained this by fertilising several
+flowers, first illegitimately, and twenty-four hours afterwards
+legitimately, with pollen taken from a peculiarly coloured variety, and all
+the seedlings were similarly coloured; this shows that the legitimate
+pollen, though applied twenty-four hours subsequently, had wholly destroyed
+or prevented the action of the previously applied illegitimate pollen.
+Again, as, in making reciprocal crosses between the same two species, there
+is occasionally a great difference in the result, so something analogous
+occurs with dimorphic plants; for a short-styled cowslip (_P. veris_)
+yields more seed when fertilised by the long-styled form, and less seed
+when fertilised by its own form, compared with a long-styled cowslip when
+fertilised in the two corresponding methods.
+
+In all these respects the forms of the same undoubted species, when
+illegitimately united, behave in exactly the same manner as do two distinct
+species when crossed. This led me carefully to observe during four years
+many seedlings, raised from several illegitimate unions. The chief result
+is that these illegitimate plants, as they may be called, are not fully
+fertile. It is possible to raise from dimorphic species, both long-styled
+and short-styled illegitimate plants, and from trimorphic plants all three
+illegitimate forms. These can then be properly united in a legitimate
+manner. When this is done, there is no apparent reason why they should not
+yield as many seeds as did their parents when legitimately fertilised. But
+such is not the case; they are all infertile, but in various degrees; some
+being so utterly and incurably sterile that they did not yield during four
+seasons a single seed or even seed-capsule. These illegitimate plants,
+which are so sterile, although united with each other in a legitimate
+manner, may be strictly compared with hybrids when crossed _inter se_, and
+it is well known how sterile these latter generally are. When, on the other
+hand, a hybrid is crossed with either pure parent-species, the sterility is
+usually much lessened: and so it is when an illegitimate plant is
+fertilised by {183} a legitimate plant. In the same manner as the sterility
+of hybrids does not always run parallel with the difficulty of making the
+first cross between the two parent species, so the sterility of certain
+illegitimate plants was unusually great, whilst the sterility of the union
+from which they were derived was by no means great. With hybrids raised
+from the same seed-capsule the degree of sterility is innately variable, so
+it is in a marked manner with illegitimate plants. Lastly, many hybrids are
+profuse and persistent flowerers, whilst other and more sterile hybrids
+produce few flowers, and are weak, miserable dwarfs; exactly similar cases
+occur with the illegitimate offspring of various dimorphic and trimorphic
+plants.
+
+Altogether there is the closest identity in character and behaviour between
+illegitimate plants and hybrids. It is hardly an exaggeration to maintain
+that the former are hybrids, but produced within the limits of the same
+species by the improper union of certain forms, whilst ordinary hybrids are
+produced from an improper union between so-called distinct species. We have
+already seen that there is the closest similarity in all respects between
+first illegitimate unions, and first crosses between distinct species. This
+will perhaps be made more fully apparent by an illustration: we may suppose
+that a botanist found two well-marked varieties (and such occur) of the
+long-styled form of the trimorphic _Lythrum salicaria_, and that he
+determined to try by crossing whether they were specifically distinct. He
+would find that they yielded only about one-fifth of the proper number of
+seed, and that they behaved in all the other above-specified respects as if
+they had been two distinct species. But to make the case sure, he would
+raise plants from his supposed hybridised seed, and he would find that the
+seedlings were miserably dwarfed and utterly sterile, and that they behaved
+in all other respects like ordinary hybrids. He might then maintain that he
+had actually proved, in accordance with the common view, that his two
+varieties were as good and as distinct species as any in the world; but he
+would be completely mistaken.
+
+The facts now given on dimorphic and trimorphic plants are important,
+because they show us, firstly, that the physiological {184} test of
+lessened fertility, both in first crosses and in hybrids, is no safe
+criterion of specific distinction; secondly, because we may conclude that
+there must be some unknown law or bond connecting the infertility of
+illegitimate unions with that of their illegitimate offspring, and we are
+thus led to extend this view to first crosses and hybrids; thirdly, because
+we find, and this seems to me of especial importance, that with trimorphic
+plants three forms of the same species exist, which when crossed in a
+particular manner are infertile, and yet these forms differ in no respect
+from each other, except in their reproductive organs,--as in the relative
+length of the stamens and pistils, in the size, form, and colour of the
+pollen-grains, in the structure of the stigma, and in, the number and size
+of the seeds. With these differences and no others, either in organisation
+or constitution, we find that the illegitimate unions and the illegitimate
+progeny of these three forms are more or less sterile, and closely resemble
+in a whole series of relations the first unions and hybrid offspring of
+distinct species. From this we may infer that the sterility of species when
+crossed and of their hybrid progeny is likewise in all probability
+exclusively due to differences confined to the reproductive system. We have
+indeed been brought to a similar conclusion by observing that the sterility
+of crossed species does not strictly coincide with their systematic
+affinity, that is, with the sum of their external resemblances; nor does it
+coincide with their similarity in general constitution. But we are more
+especially led to this same conclusion by considering reciprocal crosses,
+in which the male of one species cannot be united, or can be united with
+extreme difficulty, with the female of a second species, whilst the
+converse cross can be effected with perfect facility; for this difference
+in the facility of making reciprocal crosses, and in the fertility of their
+offspring, must be attributed either to the male or female element in the
+first species having been differentiated with reference to the sexual
+element of the second species in a higher degree than in the converse case.
+In so complex a subject as Hybridism it is of considerable importance thus
+to arrive at a definitive conclusion, namely, that the sterility which
+almost invariably follows the union of distinct {185} species depends
+exclusively on differences in their sexual constitution.
+
+       *       *       *       *       *
+
+On the principle which makes it necessary for man, whilst he is selecting
+and improving his domestic varieties, to keep them separate, it would
+clearly be advantageous to varieties in a state of nature, that is to
+incipient species, if they could be kept from blending, either through
+sexual aversion, or by becoming mutually sterile. Hence it at one time
+appeared to me probable, as it has to others, that this sterility might
+have been acquired through natural selection. On this view we must suppose
+that a shade of lessened fertility first spontaneously appeared, like any
+other modification, in certain individuals of a species when crossed with
+other individuals of the same species; and that successive slight degrees
+of infertility, from being advantageous, were slowly accumulated. This
+appears all the more probable, if we admit that the structural differences
+between the forms of dimorphic and trimorphic plants, as the length and
+curvature of the pistil, &c., have been co-adapted through natural
+selection; for if this be admitted, we can hardly avoid extending the same
+conclusion to their mutual infertility. Sterility moreover has been
+acquired through natural selection for other and widely different purposes,
+as with neuter insects in reference to their social economy. In the case of
+plants, the flowers on the circumference of the truss in the guelder-rose
+(_Viburnum opulus_) and those on the summit of the spike in the
+feather-hyacinth (_Muscari comosum_) have been rendered conspicuous, and
+apparently in consequence sterile, in order that insects might easily
+discover and visit the other flowers. But when we endeavour to apply the
+principle of natural selection to the acquirement by distinct species of
+mutual sterility, we meet with great difficulties. In the first place, it
+may be remarked that separate regions are often inhabited by groups of
+species or by single species, which when brought together and crossed are
+found to be more or less sterile; now it could clearly have been of no
+advantage to such separated species to have been rendered mutually sterile,
+and consequently this could not have been effected through natural
+selection; but it may perhaps be argued, that, if a species were rendered
+sterile with {186} some one compatriot, sterility with other species would
+follow as a necessary consequence. In the second place, it is as much
+opposed to the theory of natural selection, as to the theory of special
+creation, that in reciprocal crosses the male element of one form should
+have been rendered utterly impotent on a second form, whilst at the same
+time the male element of this second form is enabled freely to fertilise
+the first form; for this peculiar state of the reproductive system could
+not possibly be advantageous to either species.
+
+In considering the probability of natural selection having come into action
+in rendering species mutually sterile, one great difficulty will be found
+to lie in the existence of many graduated steps from slightly lessened
+fertility to absolute sterility. It may be admitted, on the principle above
+explained, that it would profit an incipient species if it were rendered in
+some slight degree sterile when crossed with its parent-form or with some
+other variety; for thus fewer bastardised and deteriorated offspring would
+be produced to commingle their blood with the new species in process of
+formation. But he who will take the trouble to reflect on the steps by
+which this first degree of sterility could be increased through natural
+selection to that higher degree which is common to so many species, and
+which is universal with species which have been differentiated to a generic
+or family rank, will find the subject extraordinarily complex. After mature
+reflection it seems to me that this could not have been effected through
+natural selection; for it could have been of no direct advantage to an
+individual animal to breed badly with another individual of a different
+variety, and thus leave few offspring; consequently such individuals could
+not have been preserved or selected. Or take the case of two species which
+in their present state, when crossed, produce few and sterile offspring;
+now, what is there which could favour the survival of those individuals
+which happened to be endowed in a slightly higher degree with mutual
+infertility and which thus approached by one small step towards absolute
+sterility? yet an advance of this kind, if the theory of natural selection
+be brought to bear, must have incessantly occurred with many species, for a
+multitude are mutually quite barren. With sterile neuter insects we have
+reason to {187} believe that modifications in their structure have been
+slowly accumulated by natural selection, from an advantage having been thus
+indirectly given to the community to which they belonged over other
+communities of the same species; but an individual animal, if rendered
+slightly sterile when crossed with some other variety, would not thus in
+itself gain any advantage, or indirectly give any advantage to its nearest
+relatives or to other individuals of the same variety, leading to their
+preservation. I infer from these considerations that, as far as animals are
+concerned, the various degrees of lessened fertility which occur with
+species when crossed cannot have been slowly accumulated by means of
+natural selection.
+
+With plants, it is possible that the case may be somewhat different. With
+many kinds, insects constantly carry pollen from neighbouring plants to the
+stigmas of each flower; and with some species this is effected by the wind.
+Now, if the pollen of a variety, when deposited on the stigma of the same
+variety, should become by spontaneous variation in ever so slight a degree
+prepotent over the pollen of other varieties, this would certainly be an
+advantage to the variety; for its own pollen would thus obliterate the
+effects of the pollen of other varieties, and prevent deterioration of
+character. And the more prepotent the variety's own pollen could be
+rendered through natural selection, the greater the advantage would be. We
+know from the researches of Gaertner that, with species which are mutually
+sterile, the pollen of each is always prepotent on its own stigma over that
+of the other species; but we do not know whether this prepotency is a
+consequence of the mutual sterility, or the sterility a consequence of the
+prepotency. If the latter view be correct, as the prepotency became
+stronger through natural selection, from being advantageous to a species in
+process of formation, so the sterility consequent on prepotency would at
+the same time be augmented; and the final result would be various degrees
+of sterility, such as occurs with existing species. This view might be
+extended to animals, if the female before each birth received several
+males, so that the sexual element of the prepotent male of her own variety
+obliterated the effects of the access of previous males belonging to other
+varieties; but we have no reason to believe, at least {188} with
+terrestrial animals, that this is the ease; as most males and females pair
+for each birth, and some few for life.
+
+On the whole we may conclude that with animals the sterility of crossed
+species has not been slowly augmented through natural selection; and as
+this sterility follows the same general laws in the vegetable as in the
+animal kingdom, it is improbable, though apparently possible, that with
+plants crossed species should have been rendered sterile by a different
+process. From this consideration, and remembering that species which have
+never co-existed in the same country, and which therefore could not have
+received any advantage from having been rendered mutually infertile, yet
+are generally sterile when crossed; and bearing in mind that in reciprocal
+crosses between the same two species there is sometimes the widest
+difference in their sterility, we must give up the belief that natural
+selection has come into play.
+
+As species have not been rendered mutually infertile through the
+accumulative action of natural selection, and as we may safely conclude,
+from the previous as well as from other and more general considerations,
+that they have not been endowed through an act of creation with this
+quality, we must infer that it has arisen incidentally during their slow
+formation in connection with other and unknown changes in their
+organisation. By a quality arising incidentally, I refer to such cases as
+different species of animals and plants being differently affected by
+poisons to which they are not naturally exposed; and this difference in
+susceptibility is clearly incidental on other and unknown differences in
+their organisation. So again the capacity in different kinds of trees to be
+grafted on each other, or on a third species, differs much, and is of no
+advantage to these trees, but is incidental on structural or functional
+differences in their woody tissues. We need not feel surprise at sterility
+incidentally resulting from crosses between distinct species,--the modified
+descendants of a common progenitor,--when we bear in mind how easily the
+reproductive system is affected by various causes--often by extremely
+slight changes in the conditions of life, by too close interbreeding, and
+by other agencies. It is well to bear in mind such cases, as that of the
+_Passiflora alata_, which recovered its self-fertility from {189} being
+grafted on a distinct species--the cases of plants which normally or
+abnormally are self-impotent, but can readily be fertilised by the pollen
+of a distinct species--and lastly the cases of individual domesticated
+animals which evince towards each other sexual incompatibility.
+
+       *       *       *       *       *
+
+We now at last come to the immediate point under discussion: how is it
+that, with some few exceptions in the case of plants, domesticated
+varieties, such as those of the dog, fowl, pigeon, several fruit-trees, and
+culinary vegetables, which differ from each other in external characters
+more than many species, are perfectly fertile when crossed, or even fertile
+in excess, whilst closely allied species are almost invariably in some
+degree sterile? We can, to a certain extent, give a satisfactory answer to
+this question. Passing over the fact that the amount of external difference
+between two species is no sure guide to their degree of mutual sterility,
+so that similar differences in the case of varieties would be no sure
+guide, we know that with species the cause lies exclusively in differences
+in their sexual constitution. Now the conditions to which domesticated
+animals and cultivated plants have been subjected, have had so little
+tendency towards modifying the reproductive system in a manner leading to
+mutual sterility, that we have good grounds for admitting the directly
+opposite doctrine of Pallas, namely, that such conditions generally
+eliminate this tendency; so that the domesticated descendants of species,
+which in their natural state would have been in some degree sterile when
+crossed, become perfectly fertile together. With plants, so far is
+cultivation from giving a tendency towards mutual sterility, that in
+several well-authenticated cases, already often alluded to, certain species
+have been affected in a very different manner, for they have become
+self-impotent, whilst still retaining the capacity of fertilising, and
+being fertilised by, distinct species. If the Pallasian doctrine of the
+elimination of sterility through long-continued domestication be admitted,
+and it can hardly be rejected, it becomes in the highest degree improbable
+that similar circumstances should commonly both induce and eliminate the
+same tendency; though in certain cases, with species having a peculiar
+constitution, sterility might occasionally be thus {190} induced. Thus, as
+I believe, we can understand why with domesticated animals varieties have
+not been produced which are mutually sterile; and why with plants only a
+few such cases have been observed, namely, by Gaertner, with certain
+varieties of maize and verbascum, by other experimentalists with varieties
+of the gourd and melon, and by Koelreuter with one kind of tobacco.
+
+With respect to varieties which have originated in a state of nature, it is
+almost hopeless to expect to prove by direct evidence that they have been
+rendered mutually sterile; for if even a trace of sterility could be
+detected, such varieties would at once be raised by almost every naturalist
+to the rank of distinct species. If, for instance, Gaertner's statement
+were fully confirmed, that the blue and red-flowered forms of the pimpernel
+(_Anagallis arvensis_) are sterile when crossed, I presume that all the
+botanists who now maintain on various grounds that these two forms are
+merely fleeting varieties, would at once admit that they were specifically
+distinct.
+
+The real difficulty in our present subject is not, as it appears to me, why
+domestic varieties have not become mutually infertile when crossed, but why
+this has so generally occurred with natural varieties as soon as they have
+been modified in a sufficient and permanent degree to take rank as species.
+We are far from precisely knowing the cause; nor is this surprising, seeing
+how profoundly ignorant we are in regard to the normal and abnormal action
+of the reproductive system. But we can see that species, owing to their
+struggle for life with numerous competitors, must have been exposed to more
+uniform conditions during long periods of time, than have been domestic
+varieties; and this may well make a wide difference in the result. For we
+know how commonly wild animals and plants, when taken from their natural
+conditions and subjected to captivity, are rendered sterile; and the
+reproductive functions of organic beings which have always lived and been
+slowly modified under natural conditions would probably in like manner be
+eminently sensitive to the influence of an unnatural cross. Domesticated
+productions, on the other hand, which, as shown by the mere fact of their
+domestication, were not originally highly sensitive to changes in their
+conditions of life, and which can now generally resist {191} with
+undiminished fertility repeated changes of conditions, might be expected to
+produce varieties, which would be little liable to have their reproductive
+powers injuriously affected by the act of crossing with other varieties
+which had originated in a like manner.
+
+Certain naturalists have recently laid too great stress, as it appears to
+me, on the difference in fertility between varieties and species when
+crossed. Some allied species of trees cannot be grafted on each other,--all
+varieties can be so grafted. Some allied animals are affected in a very
+different manner by the same poison, but with varieties no such case until
+recently was known, but now it has been proved that immunity from certain
+poisons stands in some cases in correlation with the colour of the hair.
+The period of gestation generally differs much with distinct species, but
+with varieties until lately no such difference had been observed. The time
+required for the germination of seeds differs in an analogous manner, and I
+am not aware that any difference in this respect has as yet been detected
+with varieties. Here we have various physiological differences, and no
+doubt others could be added, between one species and another of the same
+genus, which do not occur, or occur with extreme rarity, in the case of
+varieties; and these differences are apparently wholly or in chief part
+incidental on other constitutional differences, just in the same manner as
+the sterility of crossed species is incidental on differences confined to
+the sexual system. Why, then, should these latter differences, however
+serviceable they may indirectly be in keeping the inhabitants of the same
+country distinct, be thought of such paramount importance, in comparison
+with other incidental and functional differences? No sufficient answer to
+this question can be given. Hence the fact that the most distinct domestic
+varieties are, with rare exceptions, perfectly fertile when crossed, and
+produce fertile offspring, whilst closely allied species are, with rare
+exceptions, more or less sterile, is not nearly so formidable an objection
+as it appears at first to the theory of the common descent of allied
+species.
+
+       *       *       *       *       *
+
+
+{192}
+
+CHAPTER XX.
+
+SELECTION BY MAN.
+
+    SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL
+    SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN
+    SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS,
+    AND BY SEMI-CIVILIZED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED
+    TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR
+    DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS
+    SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME
+    SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF
+    SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST
+    VALUED BY MAN.
+
+The power of Selection, whether exercised by man, or brought into play
+under nature through the struggle for existence and the consequent survival
+of the fittest, absolutely depends on the variability of organic beings.
+Without variability nothing can be effected; slight individual differences,
+however, suffice for the work, and are probably the sole differences which
+are effective in the production of new species. Hence our discussion on the
+causes and laws of variability ought in strict order to have preceded our
+present subject, as well as the previous subjects of inheritance, crossing,
+&c.; but practically the present arrangement has been found the most
+convenient. Man does not attempt to cause variability; though he
+unintentionally effects this by exposing organisms to new conditions of
+life, and by crossing breeds already formed. But variability being granted,
+he works wonders. Unless some degree of selection be exercised, the free
+commingling of the individuals of the same variety soon obliterates, as we
+have previously seen, the slight differences which may arise, and gives to
+the whole body of individuals uniformity of character. In separated
+districts, long-continued exposure to different conditions of life may
+perhaps produce new races without the aid of selection; but to this
+difficult subject {193} of the direct action of the conditions of life we
+shall in a future chapter recur.
+
+When animals or plants are born with some conspicuous and firmly inherited
+new character, selection is reduced to the preservation of such
+individuals, and to the subsequent prevention of crosses; so that nothing
+more need be said on the subject. But in the great majority of cases a new
+character, or some superiority in an old character, is at first faintly
+pronounced, and is not strongly inherited; and then the full difficulty of
+selection is experienced. Indomitable patience, the finest powers of
+discrimination, and sound judgment must be exercised during many years. A
+clearly predetermined object must be kept steadily in view. Few men are
+endowed with all these qualities, especially with that of discriminating
+very slight differences; judgment can be acquired only by long experience;
+but if any of these qualities be wanting, the labour of a life may be
+thrown away. I have been astonished when celebrated breeders, whose skill
+and judgment have been proved by their success at exhibitions, have shown
+me their animals, which appeared all alike, and have assigned their reasons
+for matching this and that individual. The importance of the great
+principle of Selection mainly lies in this power of selecting scarcely
+appreciable differences, which nevertheless are found to be transmissible,
+and which can be accumulated until the result is made manifest to the eyes
+of every beholder.
+
+The principle of selection may be conveniently divided into three kinds.
+_Methodical selection_ is that which guides a man who systematically
+endeavours to modify a breed according to some predetermined standard.
+_Unconscious selection_ is that which follows from men naturally preserving
+the most valued and destroying the less valued individuals, without any
+thought of altering the breed; and undoubtedly this process slowly works
+great changes. Unconscious selection graduates into methodical, and only
+extreme cases can be distinctly separated; for he who preserves a useful or
+perfect animal will generally breed from it with the hope of getting
+offspring of the same character; but as long as he has not a predetermined
+purpose to improve the breed, he may be said to be selecting {194}
+unconsciously.[442] Lastly, we have _Natural selection_, which implies that
+the individuals which are best fitted for the complex, and in the course of
+ages changing conditions to which they are exposed, generally survive and
+procreate their kind. With domestic productions, with which alone we are
+here strictly concerned, natural selection comes to a certain extent into
+action, independently of, and even in opposition to, the will of man.
+
+       *       *       *       *       *
+
+_Methodical Selection._--What man has effected within recent times in
+England by methodical selection is clearly shown by our exhibitions of
+improved quadrupeds and fancy birds. With respect to cattle, sheep, and
+pigs, we owe their great improvement to a long series of well-known
+names--Bakewell, Colling, Ellman, Bates, Jonas Webb, Lords Leicester and
+Western, Fisher Hobbs, and others. Agricultural writers are unanimous on
+the power of selection: any number of statements to this effect could be
+quoted; a few will suffice. Youatt, a sagacious and experienced observer,
+writes,[443] the principle of selection is "that which enables the
+agriculturist, not only to modify the character of his flock, but to change
+it altogether." A great breeder of shorthorns[444] says, "In the anatomy of
+the shoulder modern breeders have made great improvements on the Ketton
+shorthorns by correcting the defect in the knuckle or shoulder-joint, and
+by laying the top of the shoulder more snugly into the crop, and thereby
+filling up the hollow behind it.... The eye has its fashion at different
+periods: at one time the eye high and outstanding from the head, and at
+another time the sleepy eye sunk into the head; but these extremes have
+merged into the medium of a full, clear, and prominent eye with a placid
+look."
+
+Again, hear what an excellent judge of pigs[445] says: "The legs {195}
+should be no longer than just to prevent the animal's belly from trailing
+on the ground. The leg is the least profitable portion of the hog, and we
+therefore require no more of it than is absolutely necessary for the
+support of the rest." Let any one compare the wild-boar with any improved
+breed, and he will see how effectually the legs have been shortened.
+
+Few persons, except breeders, are aware of the systematic care taken in
+selecting animals, and of the necessity of having a clear and almost
+prophetic vision into futurity. Lord Spencer's skill and judgment were well
+known; and he writes,[446] "It is therefore very desirable, before any man
+commences to breed either cattle or sheep, that he should make up his mind
+to the shape and qualities he wishes to obtain, and steadily pursue this
+object." Lord Somerville, in speaking of the marvellous improvement of the
+New Leicester sheep, effected by Bakewell and his successors, says, "It
+would seem as if they had first drawn a perfect form, and then given it
+life." Youatt[447] urges the necessity of annually drafting each flock, as
+many animals will certainly degenerate "from the standard of excellence,
+which the breeder has established in his own mind." Even with a bird of
+such little importance as the canary, long ago (1780-1790) rules were
+established, and a standard of perfection was fixed, according to which the
+London fanciers tried to breed the several sub-varieties.[448] A great
+winner of prizes at the Pigeon-shows,[449] in describing the Short-faced
+Almond Tumbler, says, "There are many first-rate fanciers who are
+particularly partial to what is called the goldfinch-beak, which is very
+beautiful; others say, take a full-size round cherry, then take a
+barley-corn, and judiciously placing and thrusting it into the cherry, form
+as it were your beak; and that is not all, for it will form a good head and
+beak, provided, as I said before, it is judiciously done; others take an
+oat; but as I think the goldfinch-beak the handsomest, I would advise the
+inexperienced fancier to get the head of a goldfinch, and keep it by him
+for his observation." Wonderfully different as is the beak of the
+rock-pigeon and goldfinch, undoubtedly, as far as {196} external shape and
+proportions are concerned, the end has been nearly gained.
+
+Not only should our animals be examined with the greatest care whilst
+alive, but, as Anderson remarks,[450] their carcases should be scrutinised,
+"so as to breed from the descendants of such only as, in the language of
+the butcher, cut up well." The "grain of the meat" in cattle, and its being
+well marbled with fat,[451] and the greater or less accumulation of fat in
+the abdomen of our sheep, have been attended to with success. So with
+poultry, a writer,[452] speaking of Cochin-China fowls, which are said to
+differ much in the quality of their flesh, says, "the best mode is to
+purchase two young brother-cocks, kill, dress, and serve up one; if he be
+indifferent, similarly dispose of the other, and try again; if, however, he
+be fine and well-flavoured, his brother will not be amiss for breeding
+purposes for the table."
+
+The great principle of the division of labour has been brought to bear on
+selection. In certain districts[453] "the breeding of bulls is confined to
+a very limited number of persons, who by devoting their whole attention to
+this department, are able from year to year to furnish a class of bulls
+which are steadily improving the general breed of the district." The
+rearing and letting of choice rams has long been, as is well known, a chief
+source of profit to several eminent breeders. In parts of Germany this
+principle is carried with merino sheep to an extreme point.[454] "So
+important is the proper selection of breeding animals considered, that the
+best flock-masters do not trust to their own judgment, or to that of their
+shepherds, but employ persons called 'sheep-classifiers,' who make it their
+special business to attend to this part of the management of several
+flocks, and thus to preserve, or if possible to improve, the best qualities
+of both parents in the lambs." In Saxony, "when the lambs are weaned, each
+in his turn is placed upon a table that his wool and form may be minutely
+observed. {197} The finest are selected for breeding and receive a first
+mark. When they are one year old, and prior to shearing them, another close
+examination of those previously marked takes place: those in which no
+defect can be found receive a second mark, and the rest are condemned. A
+few months afterwards a third and last scrutiny is made; the prime rams and
+ewes receive a third and final mark, but the slightest blemish is
+sufficient to cause the rejection of the animal." These sheep are bred and
+valued almost exclusively for the fineness of their wool; and the result
+corresponds with the labour bestowed on their selection. Instruments have
+been invented to measure accurately the thickness of the fibres; and "an
+Austrian fleece has been produced of which twelve hairs equalled in
+thickness one from a Leicester sheep."
+
+Throughout the world, wherever silk is produced, the greatest care is
+bestowed on selecting the cocoons from which the moths for breeding are to
+be reared. A careful cultivator[455] likewise examines the moths
+themselves, and destroys those that are not perfect. But what more
+immediately concerns us is that certain families in France devote
+themselves to raising eggs for sale.[456] In China, near Shanghai, the
+inhabitants of two small districts have the privilege of raising eggs for
+the whole surrounding country, and that they may give up their whole time
+to this business, they are interdicted by law from producing silk.[457]
+
+The care which successful breeders take in matching their birds is
+surprising. Sir John Sebright, whose fame is perpetuated by the "Sebright
+Bantam," used to spend "two and three days in examining, consulting, and
+disputing with a friend which were the best of five or six birds."[458] Mr.
+Bult, whose pouter-pigeons won so many prizes and were exported to North
+America under the charge of a man sent on purpose, told me that he always
+deliberated for several days before he matched each pair. Hence we can
+understand the advice of an eminent fancier, who writes,[459] "I would here
+particularly guard {198} you against having too great a variety of pigeons,
+otherwise you will know a little of all, but nothing about one as it ought
+to be known." Apparently it transcends the power of the human intellect to
+breed all kinds: "it is possible that there may be a few fanciers that have
+a good general knowledge of fancy pigeons; but there are many more who
+labour under the delusion of supposing they know what they do not." The
+excellence of one sub-variety, the Almond Tumbler, lies in the plumage,
+carriage, head, beak, and eye; but it is too presumptuous in the beginner
+to try for all these points. The great judge above quoted says, "there are
+some young fanciers who are over-covetous, who go for all the above five
+properties at once; they have their reward by getting nothing." We thus see
+that breeding even fancy pigeons is no simple art: we may smile at the
+solemnity of these precepts, but he who laughs will win no prizes.
+
+What methodical selection has effected for our animals is sufficiently
+proved, as already remarked, by our Exhibitions. So greatly were the sheep
+belonging to some of the earlier breeders, such as Bakewell and Lord
+Western, changed, that many persons could not be persuaded that they had
+not been crossed. Our pigs, as Mr. Corringham remarks,[460] during the last
+twenty years have undergone, through rigorous selection together with
+crossing, a complete metamorphosis. The first exhibition for poultry was
+held in the Zoological Gardens in 1845; and the improvement effected since
+that time has been great. As Mr. Baily, the great judge, remarked to me, it
+was formerly ordered that the comb of the Spanish cock should be upright,
+and in four or five years all good birds had upright combs; it was ordered
+that the Polish cock should have no comb or wattles, and now a bird thus
+furnished would be at once disqualified; beards were ordered, and out of
+fifty-seven pens lately (1860) exhibited at the Crystal Palace, all had
+beards. So it has been in many other cases. But in all cases the judges
+order only what is occasionally produced and what can be improved and
+rendered constant by selection. The steady increase of weight during the
+last few years in our {199} fowls, turkeys, ducks, and geese is notorious;
+"six-pound ducks are now common, whereas four pounds was formerly the
+average." As the actual time required to make a change has not often been
+recorded, it may be worth mentioning that it took Mr. Wicking thirteen
+years to put a clean white head on an almond tumbler's body, "a triumph,"
+says another fancier, "of which he may be justly proud."[461]
+
+Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descended
+from good milkers, for the sole purpose of improving his cattle for the
+production of cheese; he steadily tested the milk with the lactometer, and
+in eight years he increased, as I was informed by him, the product in the
+proportion of four to three. Here is a curious case[462] of steady but slow
+progress, with the end not as yet fully attained: in 1784 a race of
+silkworms was introduced into France, in which one hundred out of the
+thousand failed to produce white cocoons; but now, after careful selection
+during sixty-five generations, the proportion of yellow cocoons has been
+reduced to thirty-five in the thousand.
+
+With plants selection has been followed with the same good results as with
+animals. But the process is simpler, for plants in the great majority of
+cases bear both sexes. Nevertheless, with most kinds it is necessary to
+take as much care to prevent crosses as with animals or unisexual plants;
+but with some plants, such as peas, this care does not seem to be
+necessary. With all improved plants, excepting of course those which are
+propagated by buds, cuttings, &c., it is almost indispensable to examine
+the seedlings and destroy those which depart from the proper type. This is
+called "roguing," and is, in fact, a form of selection, like the rejection
+of inferior animals. Experienced horticulturists and agriculturists
+incessantly urge every one to preserve the finest plants for the production
+of seed.
+
+Although plants often present much more conspicuous variations than
+animals, yet the closest attention is generally requisite to detect each
+slight and favourable change. Mr. Masters relates[463] how "many a patient
+hour was devoted," whilst he was {200} young, to the detection of
+differences in peas intended for seed. Mr. Barnet[464] remarks that the old
+scarlet American strawberry was cultivated for more than a century without
+producing a single variety; and another writer observes how singular it was
+that when gardeners first began to attend to this fruit it began to vary;
+the truth no doubt being that it had always varied, but that, until slight
+varieties were selected and propagated by seed, no conspicuous result was
+obtained. The finest shades of difference in wheat have been discriminated
+and selected with almost as much care, as we see in Colonel Le Couteur's
+works, as in the case of the higher animals; but with our cereals the
+process of selection has seldom or never been long continued.
+
+It may be worth while to give a few examples of methodical selection with
+plants; but in fact the great improvement of all our anciently cultivated
+plants may be attributed to selection long carried on, in part
+methodically, and in part unconsciously. I have shown in a former chapter
+how the weight of the gooseberry has been increased by systematic selection
+and culture. The flowers of the Heartsease have been similarly increased in
+size and regularity of outline. With the Cineraria, Mr. Glenny[465] "was
+bold enough, when the flowers were ragged and starry and ill defined in
+colour, to fix a standard which was then considered outrageously high and
+impossible, and which, even if reached, it was said, we should be no
+gainers by, as it would spoil the beauty of the flowers. He maintained that
+he was right; and the event has proved it to be so." The doubling of
+flowers has several times been effected by careful selection: the Rev. W.
+Williamson,[466] after sowing during several years seed of _Anemone
+coronaria_, found a plant with one additional petal; he sowed the seed of
+this, and by perseverance in the same course obtained several varieties
+with six or seven rows of petals. The single Scotch rose was doubled, and
+yielded eight good varieties in nine or ten years.[467] The Canterbury bell
+(_Campanula medium_) was doubled by careful selection in four
+generations.[468] In four years Mr. Buckman,[469] by culture and {201}
+careful selection, converted parsnips, raised from wild seed, into a new
+and good variety. By selection during a long course of years, the early
+maturity of peas has been hastened from ten to twenty-one days.[470] A more
+curious case is offered by the beet-plant, which, since its cultivation in
+France, has almost exactly doubled its yield of sugar. This has been
+effected by the most careful selection; the specific gravity of the roots
+being regularly tested, and the best roots saved for the production of
+seed.[471]
+
+_Selection by Ancient and Semi-civilised People._
+
+In attributing so much importance to the selection of animals and plants,
+it may be objected that methodical selection would not have been carried on
+during ancient times. A distinguished naturalist considers it as absurd to
+suppose that semi-civilised people should have practised selection of any
+kind. Undoubtedly the principle has been systematically acknowledged and
+followed to a far greater extent within the last hundred years than at any
+former period, and a corresponding result has been gained; but it would be
+a great error to suppose, as we shall immediately see, that its importance
+was not recognised and acted on during the most ancient times, and by
+semi-civilised people. I should premise that many facts now to be given
+only show that care was taken in breeding; but when this is the case,
+selection is almost sure to be practised to a certain extent. We shall
+hereafter be enabled better to judge how far selection, when only
+occasionally carried on, by a few of the inhabitants of a country, will
+slowly produce a great effect.
+
+In a well-known passage in the thirtieth chapter of Genesis, rules are
+given for influencing, as was then thought possible, the colour of sheep;
+and speckled and dark breeds are spoken of as being kept separate. By the
+time of David the fleece was likened to snow. Youatt,[472] who has
+discussed all the passages in relation to breeding in the Old Testament,
+concludes that {202} at this early period "some of the best principles of
+breeding must have been steadily and long pursued." It was ordered,
+according to Moses, that "Thou shalt not let thy cattle gender with a
+diverse kind;" but mules were purchased,[473] so that at this early period
+other nations must have crossed the horse and ass. It is said[474] that
+Erichthonius, some generations before the Trojan war, had many brood-mares,
+"which by his care and judgment in the choice of stallions produced a breed
+of horses superior to any in the surrounding countries." Homer (Book v.)
+speaks of Aeneas's horses as bred from mares which were put to the steeds
+of Laomedon. Plato, in his 'Republic,' says to Glaucus, "I see that you
+raise at your house a great many dogs for the chase. Do you take care about
+breeding and pairing them? Among animals of good blood, are there not
+always some which are superior to the rest?" To which Glaucus answers in
+the affirmative.[475] Alexander the Great selected the finest Indian cattle
+to send to Macedonia to improve the breed.[476] According to Pliny,[477]
+King Pyrrhus had an especially valuable breed of oxen; and he did not
+suffer the bulls and cows to come together till four years old, that the
+breed might not degenerate. Virgil, in his Georgics (lib. iii.), gives as
+strong advice as any modern agriculturist could do, carefully to select the
+breeding stock; "to note the tribe, the lineage, and the sire; whom to
+reserve for husband of the herd;"--to brand the progeny;--to select sheep
+of the purest white, and to examine if their tongues are swarthy. We have
+seen that the Romans kept pedigrees of their pigeons, and this would have
+been a senseless proceeding had not great care been taken in breeding them.
+Columella gives detailed instructions about breeding fowls: "Let the
+breeding hens therefore be of a choice colour, a robust body, square-built,
+full-breasted, with large heads, with upright and bright-red combs. Those
+are believed to be the best bred which have five toes."[478] According to
+Tacitus, the Celts attended to the races of their domestic animals; {203}
+and Caesar states that they paid high prices to merchants for fine imported
+horses.[479] In regard to plants, Virgil speaks of yearly culling the
+largest seeds; and Celsus says, "where the corn and crop is but small, we
+must pick out the best ears of corn, and of them lay up our seed separately
+by itself."[480]
+
+Coming down the stream of time, we may be brief. At about the beginning of
+the ninth century Charlemagne expressly ordered his officers to take great
+care of his stallions; and if any proved bad or old, to forewarn him in
+good time before they were put to the mares.[481] Even in a country so
+little civilised as Ireland during the ninth century, it would appear from
+some ancient verses,[482] describing a ransom demanded by Cormac, that
+animals from particular places, or having a particular character, were
+valued. Thus it is said,--
+
+  Two pigs of the pigs of Mac Lir,
+  A ram and ewe both round and red,
+  I brought with me from Aengus.
+  I brought with me a stallion and a mare
+  From the beautiful stud of Manannan,
+  A bull and a white cow from Druim Cain.
+
+Athelstan, in 930, received as a present from Germany, running-horses; and
+he prohibited the exportation of English horses. King John imported "one
+hundred chosen stallions from Flanders."[483] On June 16th, 1305, the
+Prince of Wales wrote to the Archbishop of Canterbury, begging for the loan
+of any choice stallion, and promising its return at the end of the
+season.[484] There are numerous records at ancient periods in English
+history of the importation of choice animals of various kinds, and of
+foolish laws against their exportation. In the reigns of Henry VII. and
+VIII. it was ordered that the magistrates, at Michaelmas, should scour the
+heaths and commons, and destroy all mares beneath a certain size.[485] Some
+of our earlier kings passed laws against the slaughtering rams of any good
+breed before they were seven years old, so that they {204} might have time
+to breed. In Spain Cardinal Ximenes issued, in 1509, regulations on the
+_selection_ of good rams for breeding.[486]
+
+The Emperor Akbar Khan before the year 1600 is said to have "wonderfully
+improved" his pigeons by crossing the breeds; and this necessarily implies
+careful selection. About the same period the Dutch attended with the
+greatest care to the breeding of these birds. Belon in 1555 says that good
+managers in France examined the colour of their goslings in order to get
+geese of a white colour and better kinds. Markham in 1631 tells the breeder
+"to elect the largest and goodliest conies," and enters into minute
+details. Even with respect to seeds of plants for the flower-garden, Sir J.
+Hanmer writing about the year 1660[487] says, in "choosing seed, the best
+seed is the most weighty, and is had from the lustiest and most vigorous
+stems;" and he then gives rules about leaving only a few flowers on plants
+for seed; so that even such details were attended to in our flower-gardens
+two hundred years ago. In order to show that selection has been silently
+carried on in places where it would not have been expected, I may add that
+in the middle of the last century, in a remote part of North America, Mr.
+Cooper improved by careful selection all his vegetables, "so that they were
+greatly superior to those of any other person. When his radishes, for
+instance, are fit for use, he takes ten or twelve that he most approves,
+and plants them at least 100 yards from others that blossom at the same
+time. In the same manner he treats all his other plants, varying the
+circumstances according to their nature."[488]
+
+In the great work on China published in the last century by the Jesuits,
+and which is chiefly compiled from ancient Chinese encyclopaedias, it is
+said that with sheep "improving the breed consists in choosing with
+particular care the lambs which are destined for propagation, in nourishing
+them well, and in keeping the flocks separate." The same principles were
+applied by the Chinese to various plants and fruit-trees.[489] An {205}
+imperial edict recommends the choice of seed of remarkable size; and
+selection was practised even by imperial hands, for it is said that the
+Ya-mi, or imperial rice, was noticed at an ancient period in a field by the
+Emperor Khang-hi, was saved and cultivated in his garden, and has since
+become valuable from being the only kind which will grow north of the Great
+Wall.[490] Even with flowers, the tree paeony (_P. moutan_) has been
+cultivated, according to Chinese traditions, for 1400 years; between 200
+and 300 varieties have been raised, which are cherished like tulips
+formerly were by the Dutch.[491]
+
+Turning now to semi-civilised people and to savages: it occurred to me,
+from what I had seen of several parts of South America, where fences do not
+exist, and where the animals are of little value, that there would be
+absolutely no care in breeding or selecting them; and this to a large
+extent is true. Roulin,[492] however, describes in Colombia a naked race of
+cattle, which are not allowed to increase, on account of their delicate
+constitution. According to Azara[493] horses are often born in Paraguay
+with curly hair; but, as the natives do not like them, they are destroyed.
+On the other hand, Azara states that a hornless bull, born in 1770, was
+preserved and propagated its race. I was informed of the existence in Banda
+Oriental of a breed with reversed hair; and the extraordinary niata cattle
+first appeared and have since been kept distinct in La Plata. Hence certain
+conspicuous variations have been preserved, and others have been habitually
+destroyed, in these countries, which are so little favourable for careful
+selection. We have also seen that the inhabitants sometimes introduce
+cattle on their estates to prevent the evil effects of close interbreeding.
+On the other hand, I have heard on reliable authority that the Gauchos of
+the Pampas never take any pains in selecting the best bulls or stallions
+for breeding; and this probably accounts for the cattle and horses being
+remarkably uniform in character throughout the immense range of the
+Argentine republic.
+
+Looking to the Old World, in the Sahara Desert "The Touareg is as careful
+in the selection of his breeding Mahari {206} (a fine race of the
+dromedary) as the Arab is in that of his horse. The pedigrees are handed
+down, and many a dromedary can boast a genealogy far longer than the
+descendants of the Darley Arabian."[494] According to Pallas the Mongolians
+endeavour to breed the Yaks or horse-tailed buffaloes with white tails, for
+these are sold to the Chinese mandarins as fly-flappers; and Moorcroft,
+about seventy years after Pallas, found that white-tailed animals were
+still selected for breeding.[495]
+
+We have seen in the chapter on the Dog that savages in different parts of
+North America and in Guiana cross their dogs with wild Canidae, as did the
+ancient Gauls, according to Pliny. This was done to give their dogs
+strength and vigour, in the same way as the keepers in large warrens now
+sometimes cross their ferrets (as I have been informed by Mr. Yarrell) with
+the wild polecat, "to give them more devil." According to Varro, the wild
+ass was formerly caught and crossed with the tame animal to improve the
+breed, in the same manner as at the present day the natives of Java
+sometimes drive their cattle into the forests to cross with the wild
+Banteng (_Bos sondaicus_).[496] In Northern Siberia, among the Ostyaks the
+dogs vary in markings in different districts, but in each place they are
+spotted black and white in a remarkably uniform manner;[497] and from this
+fact alone we may infer careful breeding, more especially as the dogs of
+one locality are famed throughout the country for their superiority. I have
+heard of certain tribes of Esquimaux who take pride in their teams of dogs
+being uniformly coloured. In Guiana, as Sir R. Schomburgk informs me,[498]
+the dogs of the Turuma Indians are highly valued and extensively bartered:
+the price of a good one is the same as that given for a wife: they are kept
+in a sort of cage, and the Indians "take great care when the female is in
+season to prevent her uniting with a dog of an inferior description." The
+Indians told Sir Robert that, if a dog proved bad or useless, {207} he was
+not killed, but was left to die from sheer neglect. Hardly any nation is
+more barbarous than the Fuegians, but I hear from Mr. Bridges, the
+Catechist to the Mission, that, "when these savages have a large, strong,
+and active bitch, they take care to put her to a fine dog, and even take
+care to feed her well, that her young may be strong and well favoured."
+
+In the interior of Africa, negroes, who have not associated with white men,
+show great anxiety to improve their animals: they "always choose the larger
+and stronger males for stock:" the Malakolo were much pleased at
+Livingstone's promise to send them a bull, and some Bakalolo carried a live
+cock all the way from Loanda into the interior.[499] Further south on the
+same continent, Andersson states that he has known a Damara give two fine
+oxen for a dog which struck his fancy. The Damaras take great delight in
+having whole droves of cattle of the same colour, and they prize their oxen
+in proportion to the size of their horns. "The Namaquas have a perfect
+mania for a uniform team; and almost all the people of Southern Africa
+value their cattle next to their women, and take a pride in possessing
+animals that look high-bred." "They rarely or never make use of a handsome
+animal as a beast of burden."[500] The power of discrimination which these
+savages possess is wonderful, and they can recognise to which tribe any
+cattle belong. Mr. Andersson further informs me that the natives frequently
+match a particular bull with a particular cow.
+
+The most curious case of selection by semi-civilised people, or indeed by
+any people, which I have found recorded, is that given by Garcilazo de la
+Vega, a descendant of the Incas, as having been practised in Peru before
+the country was subjugated by the Spaniards.[501] The Incas annually held
+great hunts, when all the wild animals were driven from an immense circuit
+to a central point. The beasts of prey were first destroyed as injurious.
+The wild Guanacos and Vicunas were sheared; the old males and females
+killed, and the others set at liberty. The various kinds of deer were
+examined; the old males and females {208} were likewise killed; "but the
+young females, with a certain number of males, selected from the most
+beautiful and strong," were given their freedom. Here, then, we have
+selection by man aiding natural selection. So that the Incas followed
+exactly the reverse system of that which our Scottish sportsmen are accused
+of following, namely, of steadily killing the finest stags, thus causing
+the whole race to degenerate.[502] In regard to the domesticated llamas and
+alpacas, they were separated in the time of the Incas according to colour;
+and if by chance one in a flock was born of the wrong colour, it was
+eventually put into another flock.
+
+In the genus Auchenia there are four forms,--the Guanaco and Vicuna, found
+wild and undoubtedly distinct species; the Llama and Alpaca, known only in
+a domesticated condition. These four animals appear so different, that most
+professed naturalists, especially those who have studied these animals in
+their native country, maintain that they are specifically distinct,
+notwithstanding that no one pretends to have seen a wild llama or alpaca.
+Mr. Ledger, however, who has closely studied these animals both in Peru and
+during their exportation to Australia, and who has made many experiments on
+their propagation, adduces arguments[503] which seem to me conclusive, that
+the llama is the domesticated descendant of the guanaco, and the alpaca of
+the vicuna. And now that we know that these animals many centuries ago were
+systematically bred and selected, there is nothing surprising in the great
+amount of change which they have undergone.
+
+It appeared to me at one time probable that, though ancient and
+semi-civilised people might have attended to the improvement of their more
+useful animals in essential points, yet that they would have disregarded
+unimportant characters. But human nature is the same throughout the world:
+fashion everywhere reigns supreme, and man is apt to value whatever he may
+chance to possess. We have seen that in South America the niata cattle,
+which certainly are not made useful by their shortened faces and upturned
+nostrils, have been preserved. The Damaras of South Africa value their
+cattle for uniformity {209} of colour and enormously long horns. The
+Mongolians value their yaks for their white tails. And I shall now show
+that there is hardly any peculiarity in our most useful animals which, from
+fashion, superstition, or some other motive, has not been valued, and
+consequently preserved. With respect to cattle, "an early record,"
+according to Youatt,[504] "speaks of a hundred white cows with red ears
+being demanded as a compensation by the princes of North and South Wales.
+If the cattle were of a dark or black colour, 150 were to be presented." So
+that colour was attended to in Wales before its subjugation by England. In
+Central Africa, an ox that beats the ground with its tail is killed; and in
+South Africa some of the Damaras will not eat the flesh of a spotted ox.
+The Kaffirs value an animal with a musical voice; and "at a sale in British
+Kaffraria the low of a heifer excited so much admiration that a sharp
+competition sprung up for her possession, and she realised a considerable
+price."[505] With respect to sheep, the Chinese prefer rams without horns;
+the Tartars prefer them with spirally wound horns, because the hornless are
+thought to lose courage.[506] Some of the Damaras will not eat the flesh of
+hornless sheep. In regard to horses, at the end of the fifteenth century
+animals of the colour described as _liart pomme_ were most valued in
+France. The Arabs have a proverb, "Never buy a horse with four white feet,
+for he carries his shroud with him;"[507] the Arabs also, as we have seen,
+despise dun-coloured horses. So with dogs, Xenophon and others at an
+ancient period were prejudiced in favour of certain colours; and "white or
+slate-coloured hunting dogs were not esteemed."[508]
+
+Turning to poultry, the old Roman gourmands thought that the liver of a
+white goose was the most savoury. In Paraguay black-skinned fowls are kept
+because they are thought to be more productive, and their flesh the most
+proper for invalids.[509] In Guiana, as I am informed by Sir R. Schomburgk,
+the aborigines will not eat the flesh or eggs of the fowl, but two {210}
+races are kept distinct merely for ornament. In the Philippines, no less
+than nine sub-varieties of the game cock are kept and named, so that they
+must be separately bred.
+
+At the present time in Europe, the smallest peculiarities are carefully
+attended to in our most useful animals, either from fashion, or as a mark
+of purity of blood. Many examples could be given, two will suffice. "In the
+Western counties of England the prejudice against a white pig is nearly as
+strong as against a black one in Yorkshire." In one of the Berkshire
+sub-breeds, it is said, "the white should be confined to four white feet, a
+white spot between the eyes, and a few white hairs behind each shoulder."
+Mr. Saddler possessed "three hundred pigs, every one of which was marked in
+this manner."[510] Marshall, towards the close of the last century, in
+speaking of a change in one of the Yorkshire breeds of cattle, says the
+horns have been considerably modified, as "a clean, small, sharp horn has
+been _fashionable_ for the last twenty years."[511] In a part of Germany
+the cattle of the Race de Gfoehl are valued for many good qualities, but
+they must have horns of a particular curvature and tint, so much so that
+mechanical means are applied if they take a wrong direction; but the
+inhabitants "consider it of the highest importance that the nostrils of the
+bull should be flesh-coloured, and the eyelashes light; this is an
+indispensable condition. A calf with blue nostrils would not be purchased,
+or purchased at a very low price."[512] Therefore let no man say that any
+point or character is too trifling to be methodically attended to and
+selected by breeders.
+
+       *       *       *       *       *
+
+_Unconscious Selection._--By this term I mean, as already more than once
+explained, the preservation by man of the most valued, and the destruction
+of the least valued individuals, without any conscious intention on his
+part of altering the breed. It is difficult to offer direct proofs of the
+results which follow from this kind of selection; but the indirect evidence
+is abundant. In fact, except that in the one case man acts intentionally,
+and in the other unintentionally, there is little difference between {211}
+methodical and unconscious selection. In both cases man preserves the
+animals which are most useful or pleasing to him, and destroys or neglects
+the others. But no doubt a far more rapid result follows from methodical
+than from unconscious selection. The "roguing" of plants by gardeners, and
+the destruction by law in Henry VIII.'s reign of all under-sized mares, are
+instances of a process the reverse of selection in the ordinary sense of
+the word, but leading to the same general result. The influence of the
+destruction of individuals having a particular character is well shown by
+the necessity of killing every lamb with a trace of black about it, in
+order to keep the flock white; or again, by the effects on the average
+height of the men of France of the destructive wars of Napoleon, by which
+many tall men were killed, the short ones being left to be the fathers of
+families. This at least is the conclusion of those who have closely studied
+the subject of the conscription; and it is certain that since Napoleon's
+time the standard for the army has been lowered two or three times.
+
+Unconscious selection so blends into methodical that it is scarcely
+possible to separate them. When a fancier long ago first happened to notice
+a pigeon with an unusually short beak, or one with the tail-feathers
+unusually developed, although he bred from these birds with the distinct
+intention of propagating the variety, yet he could not have intended to
+make a short-faced tumbler or a fantail, and was far from knowing that he
+had made the first step towards this end. If he could have seen the final
+result, he would have been struck with astonishment, but, from what we know
+of the habits of fanciers, probably not with admiration. Our English
+carriers, barbs, and short-faced tumblers have been greatly modified in the
+same manner, as we may infer both from the historical evidence given in the
+chapters on the Pigeon, and from the comparison of birds brought from
+distant countries.
+
+So it has been with dogs; our present fox-hounds differ from the old
+English hound; our greyhounds have become lighter; the wolf-dog, which
+belonged to the greyhound class, has become extinct; the Scotch deer-hound
+has been modified, and is now rare. Our bulldogs differ from those which
+were formerly used for baiting bulls. Our pointers and Newfoundlands do not
+{212} closely resemble any native dog now found in the countries whence
+they were brought, These changes have been effected partly by crosses; but
+in every case the result has been governed by the strictest selection.
+Nevertheless there is no reason to suppose that man intentionally and
+methodically made the breeds exactly what they now are. As our horses
+became fleeter, and the country more cultivated and smoother, fleeter
+fox-hounds were desired and produced, but probably without any one
+distinctly foreseeing what they would become. Our pointers and setters, the
+latter almost certainly descended from large spaniels, have been greatly
+modified in accordance with fashion and the desire for increased speed.
+Wolves have become extinct, deer have become rarer, bulls are no longer
+baited, and the corresponding breeds of the dog have answered to the
+change. But we may feel almost sure that when, for instance, bulls were no
+longer baited, no man said to himself, I will now breed my dogs of smaller
+size, and thus create the present race. As circumstances changed, men
+unconsciously and slowly modified their course of selection.
+
+With race-horses selection for swiftness has been followed methodically,
+and our horses can now easily beat their progenitors. The increased size
+and different appearance of the English race-horse led a good observer in
+India to ask, "Could any one in this year of 1856, looking at our
+race-horses, conceive that they were the result of the union of the Arab
+horse and the African mare?"[513] This change has, it is probable, been
+largely effected through unconscious selection, that is, by the general
+wish to breed as fine horses as possible in each generation, combined with
+training and high feeding, but without any intention to give to them their
+present appearance. According to Youatt,[514] the introduction in Oliver
+Cromwell's time of three celebrated Eastern stallions speedily affected the
+English breed; "so that Lord Harleigh, one of the old school, complained
+that the great horse was fast disappearing." This is an excellent proof how
+carefully selection must have been attended to; for without such care, all
+traces of so small an infusion of Eastern blood would soon have been
+absorbed and {213} lost. Notwithstanding that the climate of England has
+never been esteemed particularly favourable to the horse, yet
+long-continued selection, both methodical and unconscious, together with
+that practised by the Arabs during a still longer and earlier period, has
+ended in giving us the best breed of horses in the world. Macaulay[515]
+remarks, "Two men whose authority on such subjects was held in great
+esteem, the Duke of Newcastle and Sir John Fenwick, pronounced that the
+meanest hack ever imported from Tangier would produce a finer progeny than
+could be expected from the best sire of our native breed. They would not
+readily have believed that a time would come when the princes and nobles of
+neighbouring lands would be as eager to obtain horses from England as ever
+the English had been to obtain horses from Barbary."
+
+The London dray-horse, which differs so much in appearance from any natural
+species, and which from its size has so astonished many Eastern princes,
+was probably formed by the heaviest and most powerful animals having been
+selected during many generations in Flanders and England, but without the
+least intention or expectation of creating a horse such as we now see. If
+we go back to an early period of history, we behold in the antique Greek
+statues, as Schaaffhausen has remarked,[516] a horse equally unlike a race
+or dray horse, and differing from any existing breed.
+
+The results of unconscious selection, in an early stage, are well shown in
+the difference between the flocks descended from the same stock, but
+separately reared by careful breeders. Youatt gives an excellent instance
+of this fact in the sheep belonging to Messrs. Buckley and Burgess, which
+"have been purely bred from the original stock of Mr. Bakewell for upwards
+of fifty years. There is not a suspicion existing in the mind of any one at
+all acquainted with the subject that the owner of either flock has deviated
+in any one instance from the pure blood of Mr. Bakewell's flock; yet the
+difference between the sheep possessed by these two gentlemen is so great,
+that they have the appearance of being quite different varieties."[517] I
+have seen several analogous and {214} well-marked cases with pigeons: for
+instance, I had a family of barbs, descended from those long bred by Sir J.
+Sebright, and another family long bred by another fancier, and the two
+families plainly differed from each other. Nathusius--and a more competent
+witness could not be cited--observes that, though the Shorthorns are
+remarkably uniform inn appearance (except in colouring), yet that the
+individual character and wishes of each breeder become impressed on his
+cattle, so that different herds differ slightly from each other.[518] The
+Hereford cattle assumed their present well-marked character soon after the
+year 1769, through careful selection by Mr. Tomkins,[519] and the breed has
+lately split into two strains--one strain having a white face, and
+differing slightly, it is said,[520] in some other points; but there is no
+reason to believe that this split, the origin of which is unknown, was
+intentionally made; it may with much more probability be attributed to
+different breeders having attended to different points. So again, the
+Berkshire breed of swine in the year 1810 had greatly changed from what it
+had been in 1780; and since 1810 at least two distinct sub-breeds have
+borne this same name.[521] When we bear in mind how rapidly all animals
+increase, and that some must be annually slaughtered and some saved for
+breeding, then, if the same breeder during a long course of years
+deliberately settles which shall be saved and which shall be killed, it is
+almost inevitable that his individual frame of mind will influence the
+character of his stock, without his having had any intention to modify the
+breed or form a new strain.
+
+Unconscious selection in the strictest sense of the word, that is, the
+saving of the more useful animals and the neglect or slaughter of the less
+useful, without any thought of the future, must have gone on occasionally
+from the remotest period and amongst the most barbarous nations. Savages
+often suffer from famines, and are sometimes expelled by war from their own
+homes. In such cases it can hardly be doubted that they would save their
+most useful animals. When the Fuegians {215} are hard pressed by want, they
+kill their old women for food rather than their dogs; for, as we were
+assured, "old women no use--dogs catch otters." The same sound sense would
+surely lead them to preserve their more useful dogs when still harder
+pressed by famine. Mr. Oldfield, who has seen so much of the aborigines of
+Australia, informs me that "they are all very glad to get a European
+kangaroo dog, and several instances have been known of the father killing
+his own infant that the mother might suckle the much-prized puppy."
+Different kinds of dogs would be useful to the Australian for hunting
+opossums and kangaroos, and to the Fuegian for catching fish and otters;
+and the occasional preservation in the two countries of the most useful
+animals would ultimately lead to the formation of two widely distinct
+breeds.
+
+       *       *       *       *       *
+
+With plants, from the earliest dawn of civilisation, the best variety which
+at each period was known would generally have been cultivated and its seeds
+occasionally sown; so that there will have been some selection from an
+extremely remote period, but without any prefixed standard of excellence or
+thought of the future. We at the present day profit by a course of
+selection occasionally and unconsciously carried on during thousands of
+years. This is proved in an interesting manner by Oswald Heer's researches
+on the lake-inhabitants of Switzerland, as given in a former chapter; for
+he shows that the grain and seed of our present varieties of wheat, barley,
+oats, peas, beans, lentils, and poppy, exceed in size those which were
+cultivated in Switzerland during the Neolithic and Bronze periods. These
+ancient people, during the Neolithic period, possessed also a crab
+considerably larger than that now growing wild on the Jura.[522] The pears
+described by Pliny were evidently extremely inferior in quality to our
+present pears. We can realise the effects of long-continued selection and
+cultivation in another way, for would any one in his senses expect to raise
+a first-rate apple from the seed of a truly wild crab, or a luscious
+melting pear from the wild pear? Alphonse De Candolle informs me that he
+has lately seen on an ancient mosaic at Rome a representation of {216} the
+melon; and as the Romans, who were such gourmands, are silent on this
+fruit, he infers that the melon has been greatly ameliorated since the
+classical period.
+
+Coming to later times, Buffon,[523] on comparing the flowers, fruit, and
+vegetables which were then cultivated, with some excellent drawings made a
+hundred and fifty years previously, was struck with surprise at the great
+improvement which had been effected; and remarks that these ancient flowers
+and vegetables would now be rejected, not only by a florist but by a
+village gardener. Since the time of Buffon the work of improvement has
+steadily and rapidly gone on. Every florist who compares our present
+flowers with those figured in books published not long since, is astonished
+at the change. A well-known amateur,[524] in speaking of the varieties of
+Pelargonium raised by Mr. Garth only twenty-two years before, remarks,
+"what a rage they excited: surely we had attained perfection, it was said;
+and now not one of the flowers of those days will be looked at. But none
+the less is the debt of gratitude which we owe to those who saw what was to
+be done, and did it." Mr. Paul, the well-known horticulturist, in writing
+of the same flower,[525] says he remembers when young being delighted with
+the portraits in Sweet's work; "but what are they in point of beauty
+compared with the Pelargoniums of this day? Here again nature did not
+advance by leaps; the improvement was gradual, and, if we had neglected
+those very gradual advances, we must have foregone the present grand
+results." How well this practical horticulturist appreciates and
+illustrates the gradual and accumulative force of selection! The Dahlia has
+advanced in beauty in a like manner; the line of improvement being guided
+by fashion, and by the successive modifications which the flower slowly
+underwent.[526] A steady and gradual change has been noticed in many other
+flowers: thus an old florist,[527] after describing the leading varieties
+of the Pink which were grown in 1813, adds, "the pinks of those days would
+now be scarcely grown as border-flowers." The improvement of {217} so many
+flowers and the number of the varieties which have been raised is all the
+more striking when we hear that the earliest known flower-garden in Europe,
+namely at Padua, dates only from the year 1545.[528]
+
+       *       *       *       *       *
+
+_Effects of Selection, as shown by the parts most valued by man presenting
+the greatest amount of Difference._--The power of long-continued selection,
+whether methodical or unconscious, or both combined, is well shown in a
+general way, namely, by the comparison of the differences between the
+varieties of distinct species, which are valued for different parts, such
+as for the leaves, or stems, or tubers, the seed, or fruit, or flowers.
+Whatever part man values most, that part will be found to present the
+greatest amount of difference. With trees cultivated for their fruit,
+Sageret remarks that the fruit is larger than in the parent-species, whilst
+with those cultivated for the seed, as with nuts, walnuts, almonds,
+chesnuts, &c., it is the seed itself which is larger; and he accounts for
+this fact by the fruit in the one case, and by the seed in the other,
+having been carefully attended to and selected during many ages. Gallesio
+has made the same observation. Godron insists on the diversity of the tuber
+in the potato, of the bulb in the onion, and of the fruit in the melon; and
+on the close similarity in these same plants of the other parts.[529]
+
+In order to judge how far my own impression on this subject was correct, I
+cultivated numerous varieties of the same species close to each other. The
+comparison of the amount of difference between widely different organs is
+necessarily vague; I will therefore give the results in only a few cases.
+We have previously seen in the ninth chapter how greatly the varieties of
+the cabbage differ in their foliage and stems, which are the selected
+parts, and how closely they resembled each other in their flowers,
+capsules, and seeds. In seven varieties of the radish, the roots differed
+greatly in colour and shape, but no difference {218} whatever could be
+detected in their foliage, flowers, or seeds. Now what a contrast is
+presented, if we compare the flowers of the varieties of these two plants
+with those of any species cultivated in our flower-gardens for ornament; or
+if we compare their seeds with those of the varieties of maize, peas,
+beans, &c., which are valued and cultivated for their seeds. In the ninth
+chapter it was shown that the varieties of the pea differ but little except
+in the tallness of the plant, moderately in the shape of the pod, and
+greatly in the pea itself, and these are all selected points. The
+varieties, however, of the _Pois sans parchemin_ differ much more in their
+pods, and these are eaten and valued. I cultivated twelve varieties of the
+common bean; one alone, the Dwarf Fan, differed considerably in general
+appearance; two differed in the colour of their flowers, one being an
+albino, and the other being wholly instead of partially purple; several
+differed considerably in the shape and size of the pod, but far more in the
+bean itself, and this is the valued and selected part. Toker's bean, for
+instance, is twice-and-a-half as long and broad as the horse-bean, and is
+much thinner and of a different shape.
+
+The varieties of the gooseberry, as formerly described, differ much in
+their fruit, but hardly perceptibly in their flowers or organs of
+vegetation. With the plum, the differences likewise appear to be greater in
+the fruit than in the flowers or leaves. On the other hand, the seed of the
+strawberry, which corresponds with the fruit of the plum, differs hardly at
+all; whilst every one knows how greatly the fruit--that is, the enlarged
+receptacle--differs in the several varieties. In apples, pears, and peaches
+the flowers and leaves differ considerably, but not, as far as I can judge,
+in proportion with the fruit. The Chinese double-flowering peaches, on the
+other hand, show that varieties of this tree have been formed, which differ
+more in the flower than in fruit. If, as is highly probable, the peach is
+the modified descendant of the almond, a surprising amount of change has
+been effected in the same species, in the fleshy covering of the former and
+in the kernels of the latter.
+
+When parts stand in such close relation to each other as the fleshy
+covering of the fruit (whatever its homological nature may be) and the
+seed, when one part is modified, so generally is the other, but by no means
+necessarily in the same degree. With {219} the plum-tree, for instance,
+some varieties produce plums which are nearly alike, but include stones
+extremely dissimilar in shape; whilst conversely other varieties produce
+dissimilar fruit with barely distinguishable stones; and generally the
+stones, though they have never been subjected to selection, differ greatly
+in the several varieties of the plum. In other cases organs which are not
+manifestly related, through some unknown bond vary together, and are
+consequently liable, without any intention on man's part, to be
+simultaneously acted on by selection. Thus the varieties of the stock
+(Matthiola) have been selected solely for the beauty of their flowers, but
+the seeds differ greatly in colour and somewhat in size. Varieties of the
+lettuce have been selected solely on account of their leaves, yet produce
+seeds which likewise differ in colour. Generally, through the law of
+correlation, when a variety differs greatly from its fellow-varieties in
+any one character, it differs to a certain extent in several other
+characters. I observed this fact when I cultivated together many varieties
+of the same species, for I used first to make a list of the varieties which
+differed most from each other in their foliage and manner of growth,
+afterwards of those that differed most in their flowers, then in their
+seed-capsules, and lastly in their mature seed; and I found that the same
+names generally occurred in two, three, or four of the successive lists.
+Nevertheless the greatest amount of difference between the varieties was
+always exhibited, as far as I could judge, by that part or organ for which
+the plant was cultivated.
+
+When we bear in mind that each plant was at first cultivated because useful
+to man, and that its variation was a subsequent, often a long subsequent,
+event, we cannot explain the greater amount of diversity in the valuable
+parts by supposing that species endowed with an especial tendency to vary
+in any particular manner, were originally chosen. We must attribute the
+result to the variations in these parts having been successively preserved,
+and thus continually augmented; whilst other variations, excepting such as
+inevitably appeared through correlation, were neglected and lost. Hence we
+may infer that most plants might be made, through long-continued selection,
+to yield races as different from each other in any character {220} as they
+now are in those parts for which they are valued and cultivated.
+
+With animals we see something of the same kind; but they have not been
+domesticated in sufficient number or yielded sufficient varieties for a
+fair comparison. Sheep are valued for their wool, and the wool differs much
+more in the several races than the hair in cattle. Neither sheep, goats,
+European cattle, nor pigs are valued for their fleetness or strength; and
+we do not possess breeds differing in these respects like the race-horse
+and dray-horse. But fleetness and strength are valued in camels and dogs;
+and we have with the former the swift dromedary and heavy camel; with the
+latter the greyhound and mastiff. But dogs are valued even in a higher
+degree for their mental qualities and senses; and every one knows how
+greatly the races differ in these respects. On the other hand, where the
+dog is valued solely to serve for food, as in the Polynesian islands and
+China, it is described as an extremely stupid animal.[530] Blumenbach
+remarks that "many dogs, such as the badger-dog, have a build so marked and
+so appropriate for particular purposes, that I should find it very
+difficult to persuade myself that this astonishing figure was an accidental
+consequence of degeneration."[531] But had Blumenbach reflected on the
+great principle of selection, he would not have used the term degeneration,
+and he would not have been astonished that dogs and other animals should
+become excellently adapted for the service of man.
+
+On the whole we may conclude that whatever part or character is most
+valued--whether the leaves, stems, tubers, bulbs, flowers, fruit, or seed
+of plants, or the size, strength, fleetness, hairy covering, or intellect
+of animals--that character will almost invariably be found to present the
+greatest amount of difference both in kind and degree. And this result may
+be safely attributed to man having preserved during a long course of
+generations the variations which were useful to him, and neglected the
+others.
+
+I will conclude this chapter by some remarks on an important subject. With
+animals such as the giraffe, of which {221} the whole structure is
+admirably co-ordinated for certain purposes, it has been supposed that all
+the parts must have been simultaneously modified; and it has been argued
+that, on the principle of natural selection, this is scarcely possible. But
+in thus arguing, it has been tacitly assumed that the variations must have
+been abrupt and great. No doubt, if the neck of a ruminant were suddenly to
+become greatly elongated, the fore limbs and back would have to be
+simultaneously strengthened and modified; but it cannot be denied that an
+animal might have its neck, or head, or tongue, or fore-limbs elongated a
+very little without any corresponding modification in other parts of the
+body; and animals thus slightly modified would, during a dearth, have a
+slight advantage, and be enabled to browse on higher twigs, and thus
+survive. A few mouthfuls more or less every day would make all the
+difference between life and death. By the repetition of the same process,
+and by the occasional intercrossing of the survivors, there would be some
+progress, slow and fluctuating though it would be, towards the admirably
+co-ordinated structure of the giraffe. If the short-faced tumbler-pigeon,
+with its small conical beak, globular head, rounded body, short wings, and
+small feet--characters which appear all in harmony--had been a natural
+species, its whole structure would have been viewed as well fitted for its
+life; but in this case we know that inexperienced breeders are urged to
+attend to point after point, and not to attempt improving the whole
+structure at the same time. Look at the greyhound, that perfect image of
+grace, symmetry, and vigour; no natural species can boast of a more
+admirably co-ordinated structure, with its tapering head, slim body, deep
+chest, tucked-up abdomen, rat-like tail, and long muscular limbs, all
+adapted for extreme fleetness, and for running down weak prey. Now, from
+what we see of the variability of animals, and from what we know of the
+method which different men follow in improving their stock--some chiefly
+attending to one point, others to another point, others again correcting
+defects by crosses, and so forth--we may feel assured that if we could see
+the long line of ancestors of a first-rate greyhound, up to its wild
+wolf-like progenitor, we should behold an infinite number of the finest
+gradations, sometimes in one character and sometimes in another, but all
+leading towards our {222} present perfect type. By small and doubtful steps
+such as these, nature, as we may confidently believe, has progressed on her
+grand march of improvement and development.
+
+A similar line of reasoning is as applicable to separate organs as to the
+whole organisation. A writer[532] has recently maintained that "it is
+probably no exaggeration to suppose that, in order to improve such an organ
+as the eye at all, it must be improved in ten different ways at once. And
+the improbability of any complex organ being produced and brought to
+perfection in any such way is an improbability of the same kind and degree
+as that of producing a poem or a mathematical demonstration by throwing
+letters at random on a table." If the eye were abruptly and greatly
+modified, no doubt many parts would have to be simultaneously altered, in
+order that the organ should remain serviceable.
+
+But is this the case with smaller changes? There are persons who can see
+distinctly only in a dull light, and this condition depends, I believe, on
+the abnormal sensitiveness of the retina, and is known to be inherited.
+Now, if a bird, for instance, received some great advantage from seeing
+well in the twilight, all the individuals with the most sensitive retina
+would succeed best and be the most likely to survive; and why should not
+all those which happened to have the eye itself a little larger, or the
+pupil capable of greater dilatation, be likewise preserved, whether or not
+these modifications were strictly simultaneous? These individuals would
+subsequently intercross and blend their respective advantages. By such
+slight successive changes, the eye of a diurnal bird would be brought into
+the condition of that of an owl, which has often been advanced as an
+excellent instance of adaptation. Short-sight, which is often inherited,
+permits a person to see distinctly a minute object at so near a distance
+that it would be indistinct to ordinary eyes; and here we have a capacity
+which might be serviceable under certain conditions, abruptly gained. The
+Fuegians on board the {223} Beagle could certainly see distant objects more
+distinctly than our sailors with all their long practice; I do not know
+whether this depends on nervous sensitiveness or on the power of adjustment
+in the focus; but this capacity for distant vision might, it is probable,
+be slightly augmented by successive modifications of either kind.
+Amphibious animals, which are enabled to see both in the water and in the
+air, require and possess, as M. Plateau has shown,[533] eyes constructed on
+the following plan: "the cornea is always flat, or at least much flattened
+in front of the crystalline and over a space equal to the diameter of that
+lens, whilst the lateral portions may be much curved." The crystalline is
+very nearly a sphere, and the humours have nearly the same density as
+water. Now, as a terrestrial animal slowly became more and more aquatic in
+its habits, very slight changes, first in the curvature of the cornea or
+crystalline, and then in the density of the humours, or conversely, might
+successively occur, and would be advantageous to the animal whilst under
+water, without serious detriment to its power of vision in the air. It is
+of course impossible to conjecture by what steps the fundamental structure
+of the eye in the Vertebrata was originally acquired, for we know
+absolutely nothing about this organ in the first progenitors of the class.
+With respect to the lowest animals in the scale, the transitional states
+through which the eye at first probably passed, can by the aid of analogy
+be indicated, as I have attempted to show in my 'Origin of Species.'[534]
+
+       *       *       *       *       *
+
+
+{224}
+
+CHAPTER XXI.
+
+SELECTION, _continued_.
+
+    NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH
+    APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES
+    FAVOURABLE TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE
+    NATURE OF THE CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE
+    INDISPENSABLE--THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS
+    ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE
+    NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION--TENDENCY IN MAN
+    TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING
+    TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE--CHARACTERS
+    CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY
+    VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE
+    VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE
+    POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC
+    RACES HAVE ORIGINATED--SUMMARY.
+
+_Natural Selection, or the Survival of the Fittest, as affecting domestic
+productions._--We know little on this head. But as animals kept by savages
+have to provide their own food, either entirely or to a large extent,
+throughout the year, it can hardly be doubted that, in different countries,
+varieties differing in constitution and in various characters would succeed
+best, and so be naturally selected. Hence perhaps it is that the few
+domesticated animals kept by savages partake, as has been remarked by more
+than one writer, of the wild appearance of their masters, and likewise
+resemble natural species. Even in long-civilised countries, at least in the
+wilder parts, natural selection must act on our domestic races. It is
+obvious that varieties, having very different habits, constitution, and
+structure, would succeed best on mountains and on rich lowland pastures.
+For example, the improved Leicester sheep were formerly taken to the
+Lammermuir Hills; but an intelligent sheep-master reported that "our coarse
+lean pastures were unequal to the task of supporting such heavy-bodied
+sheep; and they gradually dwindled away into less and less bulk: {225} each
+generation was inferior to the preceding one; and when the spring was
+severe, seldom more than two-thirds of the lambs survived the ravages of
+the storms."[535] So with the mountain cattle of North Wales and the
+Hebrides, it has been found that they could not withstand being crossed
+with the larger and more delicate lowland breeds. Two French naturalists,
+in describing the horses of Circassia, remark that, subjected as they are
+to extreme vicissitudes of climate, having to search for scanty pasture,
+and exposed to constant danger from wolves, the strongest and most vigorous
+alone survive.[536]
+
+Every one must have been struck with the surpassing grace, strength, and
+vigour of the Game-cock, with its bold and confident air, its long, yet
+firm neck, compact body, powerful and closely pressed wings, muscular
+thighs, strong beak massive at the base, dense and sharp spurs set low on
+the legs for delivering the fatal blow, and its compact, glossy, and
+mail-like plumage serving as a defence. Now the English game-cock has not
+only been improved during many years by man's careful selection, but in
+addition, as Mr. Tegetmeier has remarked,[537] by a kind of natural
+selection, for the strongest, most active and courageous birds have
+stricken down their antagonists in the cockpit, generation after
+generation, and have subsequently served as the progenitors of their kind.
+
+In Great Britain, in former times, almost every district had its own breed
+of cattle and sheep; "they were indigenous to the soil, climate, and
+pasturage of the locality on which they grazed: they seemed to have been
+formed for it and by it."[538] But in this case we are quite unable to
+disentangle the effects of the direct action of the conditions of life,--of
+use or habit--of natural selection--and of that kind of selection which we
+have seen is occasionally and unconsciously followed by man even during the
+rudest periods of history.
+
+Let us now look to the action of natural selection on special characters.
+Although nature is difficult to resist, yet man often strives against her
+power, and sometimes, as we shall see, with {226} success. From the facts
+to be given, it will also be seen that natural selection would powerfully
+affect many of our domestic productions if left unprotected. This is a
+point of much interest, for we thus learn that differences apparently of
+very slight importance would certainly determine the survival of a form
+when forced to struggle for its own existence. It may have occurred to some
+naturalists, as it formerly did to me, that, though selection acting under
+natural conditions would determine the structure of all important organs,
+yet that it could not affect characters which are esteemed by us of little
+importance; but this is an error to which we are eminently liable, from our
+ignorance of what characters are of real value to each living creature.
+
+When man attempts to breed an animal with some serious defect in structure,
+or in the mutual relation of parts, he will either partially or completely
+fail, or encounter much difficulty; and this is in fact a form of natural
+selection. We have seen that the attempt was once made in Yorkshire to
+breed cattle with enormous buttocks, but the cows perished so often in
+bringing forth their calves, that the attempt had to be given up. In
+rearing short-faced tumblers, Mr. Eaton says,[539] "I am convinced that
+better head and beak birds have perished in the shell than ever were
+hatched; the reason being that the amazingly short-faced bird cannot reach
+and break the shell with its beak, and so perishes." Here is a more curious
+case, in which natural selection comes into play only at long intervals of
+time: during ordinary seasons the Niata cattle can graze as well as others,
+but occasionally, as from 1827 to 1830, the plains of La Plata suffer from
+long-continued droughts and the pasture is burnt up; at such times common
+cattle and horses perish by the thousand, but many survive by browsing on
+twigs, reeds, &c.; this the Niata cattle cannot so well effect from their
+upturned jaws and the shape of their lips; consequently, if not attended
+to, they perish before the other cattle. In Colombia, according to Roulin,
+there is a breed of nearly hairless cattle, called Pelones; these succeed
+in their native hot district, but are found too tender for the Cordillera;
+in this case, natural selection {227} determines only the range of the
+variety. It is obvious that a host of artificial races could never survive
+in a state of nature;--such as Italian greyhounds,--hairless and almost
+toothless Turkish dogs,--fantail pigeons, which cannot fly well against a
+strong wind,--barbs with their vision impeded by their eye-wattle,--Polish
+fowls with their vision impeded by their great topknots,--hornless bulls
+and rams which consequently cannot cope with other males, and thus have a
+poor chance of leaving offspring,--seedless plants, and many other such
+cases.
+
+Colour is generally esteemed by the systematic naturalist as unimportant:
+let us, therefore, see how far it indirectly affects our domestic
+productions, and how far it would affect them if they were left exposed to
+the full force of natural selection. In a future chapter I shall have to
+show that constitutional peculiarities of the strangest kind, entailing
+liability to the action of certain poisons, are correlated with the colour
+of the skin. I will here give a single case, on the high authority of
+Professor Wyman; he informs me that, being surprised at all the pigs in a
+part of Virginia being black, he made inquiries, and ascertained that these
+animals feed on the roots of the _Lachnanthes tinctoria_, which colours
+their bones pink, and, excepting in the case of the black varieties, causes
+the hoofs to drop off. Hence, as one of the squatters remarked, "we select
+the black members of the litter for raising, as they alone have a good
+chance of living." So that here we have artificial and natural selection
+working hand in hand. I may add that in the Tarentino the inhabitants keep
+black sheep alone, because the _Hypericum crispum_ abounds there; and this
+plant does not injure black sheep, but kills the white ones in about a
+fortnight's time.[540]
+
+Complexion, and liability to certain diseases, are believed to run together
+in man and the lower animals. Thus white terriers suffer more than terriers
+of any other colour from the fatal Distemper.[541] In North America
+plum-trees are liable to a disease which Downing[542] believes is not
+caused by insects; the kinds bearing purple fruit are most affected, "and
+we have never known the green or yellow fruited varieties infected {228}
+until the other sorts had first become filled with the knots." On the other
+hand, peaches in North America suffer much from a disease called the
+_yellows_, which seems to be peculiar to that continent, and "more than
+nine-tenths of the victims, when the disease first appeared, were the
+yellow-fleshed peaches. The white-fleshed kinds are much more rarely
+attacked; in some parts of the country never." In Mauritius, the white
+sugar-canes have of late years been so severely attacked by a disease, that
+many planters have been compelled to give up growing this variety (although
+fresh plants were imported from China for trial), and cultivate only red
+canes.[543] Now, if these plants had been forced to struggle with other
+competing plants and enemies, there cannot be a doubt that the colour of
+the flesh or skin of the fruit, unimportant as these characters are
+considered, would have rigorously determined their existence.
+
+Liability to the attacks of parasites is also connected with colour. It
+appears that white chickens are certainly more subject than dark-coloured
+chickens to the _gapes_, which is caused by a parasitic worm in the
+trachea.[544] On the other hand, experience has shown that in France the
+caterpillars which produce white cocoons resist the deadly fungus better
+than those producing yellow cocoons.[545] Analogous facts have been
+observed with plants: a new and beautiful white onion, imported from
+France, though planted close to other kinds, was alone attacked by a
+parasitic fungus.[546] White verbenas are especially liable to mildew.[547]
+Near Malaga, during an early period of the vine-disease, the green sorts
+suffered most; "and red and black grapes, even when interwoven with the
+sick plants, suffered not at all." In France whole groups of varieties were
+comparatively free, and others, such as the Chasselas, did not afford a
+single fortunate exception; but I do not know whether any correlation
+between colour and liability to disease was here observed.[548] In a former
+chapter it was shown how curiously liable one variety of the strawberry is
+to mildew.
+
+{229}
+
+It is certain that insects regulate in many cases the range and even the
+existence of the higher animals, whilst living under their natural
+conditions. Under domestication light-coloured animals suffer most: in
+Thuringia[549] the inhabitants do not like grey, white, or pale cattle,
+because they are much more troubled by various kinds of flies than the
+brown, red, or black cattle. An Albino negro, it has been remarked,[550]
+was peculiarly sensitive to the bites of insects. In the West Indies[551]
+it is said that "the only horned cattle fit for work are those which have a
+good deal of black in them. The white are terribly tormented by the
+insects; and they are weak and sluggish in proportion to the white."
+
+In Devonshire there is a prejudice against white pigs, because it is
+believed that the sun blisters them when turned out;[552] and I knew a man
+who would not keep white pigs in Kent, for the same reason. The scorching
+of flowers by the sun seems likewise to depend much on colour; thus, dark
+pelargoniums suffer most; and from various accounts it is clear that the
+cloth-of-gold variety will not withstand a degree of exposure to sunshine
+which other varieties enjoy. Another amateur asserts that not only all
+dark-coloured verbenas, but likewise scarlets, suffer from the sun; "the
+paler kinds stand better, and pale blue is perhaps the best of all." So
+again with the heartsease (_Viola tricolor_); hot weather suits the
+blotched sorts, whilst it destroys the beautiful markings of some other
+kinds.[553] During one extremely cold season in Holland all red-flowered
+hyacinths were observed to be very inferior in quality. It is believed by
+many agriculturists that red wheat is hardier in northern climates than
+white wheat.[554]
+
+With animals, white varieties from being conspicuous are the most liable to
+be attacked by beasts and birds of prey. In parts of France and Germany
+where hawks abound, persons are advised not to keep white pigeons; for, as
+Parmentier says, "it {230} is certain that in a flock the white always
+first fall victims to the kite." In Belgium, where so many societies have
+been established for the flight of carrier-pigeons, white is the one colour
+which for the same reason is disliked.[555] On the other hand, it is said
+that the sea-eagle (_Falco ossifragus_, Linn.) on the west coast of Ireland
+picks out the black fowls, so that "the villagers avoid as much as possible
+rearing birds of that colour." M. Daudin,[556] speaking of white rabbits
+kept in warrens in Russia, remarks that their colour is a great
+disadvantage, as they are thus more exposed to attack, and can be seen
+during bright nights from a distance. A gentleman in Kent, who failed to
+stock his woods with a nearly white and hardy kind of rabbit, accounted in
+the same manner for their early disappearance. Any one who will watch a
+white cat prowling after her prey will soon perceive under what a
+disadvantage she lies.
+
+The white Tartarian cherry, "owing either to its colour being so much like
+that of the leaves, or to the fruit always appearing from a distance
+unripe," is not so readily attacked by birds as other sorts. The
+yellow-fruited raspberry, which generally comes nearly true by seed, "is
+very little molested by birds, who evidently are not fond of it; so that
+nets may be dispensed with in places where nothing else will protect the
+red fruit."[557] This immunity, though a benefit to the gardener, would be
+a disadvantage in a state of nature both to the cherry and raspberry, as
+their dissemination depends on birds. I noticed during several winters that
+some trees of the yellow-berried holly, which were raised from seed from a
+wild tree found by my father, remained covered with fruit, whilst not a
+scarlet berry could be seen on the adjoining trees of the common kind. A
+friend informs me that a mountain-ash (_Pyrus aucuparia_) growing in his
+garden bears berries which, though not differently coloured, are always
+devoured by birds before those on the other trees. This variety of the
+mountain-ash would thus be more freely disseminated, and the yellow-berried
+variety of the holly less freely, than the common varieties of these two
+trees.
+
+{231}
+
+Independently of colour, other trifling differences are sometimes found to
+be of importance to plants under cultivation, and would be of paramount
+importance if they had to fight their own battle and to struggle with many
+competitors. The thin-shelled peas, called _pois sans parchemin_, are
+attacked by birds[558] much more than common peas. On the other hand, the
+purple-podded pea, which has a hard shell, escaped the attacks of tomtits
+(_Parus major_) in my garden far better than any other kind. The
+thin-shelled walnut likewise suffers greatly from the tomtit.[559] These
+same birds have been observed to pass over and thus favour the filbert,
+destroying only the other kinds of nuts which grew in the same
+orchard.[560]
+
+Certain varieties of the pear have soft bark, and these suffer severely
+from boring wood-beetles; whilst other varieties are known to resist their
+attacks much better.[561] In North America the smoothness, or absence of
+down on the fruit, makes a great difference in the attacks of the weevil,
+"which is the uncompromising foe of all smooth stone-fruits;" and the
+cultivator "has the frequent mortification of seeing nearly all, or indeed
+often the whole crop, fall from the trees when half or two-thirds grown."
+Hence the nectarine suffers more than the peach. A particular variety of
+the Morello cherry, raised in North America, is without any assignable
+cause more liable to be injured by this same insect than other
+cherry-trees.[562] From some unknown cause, the Winter Majetin apple enjoys
+the great advantage of not being infested by the coccus. On the other hand,
+a particular case has been recorded in which aphides confined themselves to
+the Winter Nelis pear, and touched no other kind in an extensive
+orchard.[563] The existence of minute glands on the leaves of peaches,
+nectarines, and apricots, would not be esteemed by botanists as a character
+of the least importance, for they are present or absent in closely related
+sub-varieties, descended from the same parent-tree; yet there is good
+evidence[564] that the {232} absence of glands leads to mildew, which is
+highly injurious to these trees.
+
+A difference either in flavour or in the amount of nutriment in certain
+varieties causes them to be more eagerly attacked by various enemies than
+other varieties of the same species. Bullfinches (_Pyrrhula vulgaris_)
+injure our fruit-trees by devouring the flower-buds, and a pair of these
+birds have been seen "to denude a large plum-tree in a couple of days of
+almost every bud;" but certain varieties[565] of the apple and thorn
+(_Crataegus oxyacantha_) are more especially liable to be attacked. A
+striking instance of this was observed in Mr. Rivers's garden, in which two
+rows of a particular variety of plum[566] had to be carefully protected, as
+they were usually stripped of all their buds during the winter, whilst
+other sorts growing near them escaped. The root (or enlarged stem) of
+Laing's Swedish turnip is preferred by hares, and therefore suffers more
+than other varieties. Hares and rabbits eat down common rye before St.
+John's-day-rye, when both grow together.[567] In the South of France, when
+an orchard of almond-trees is formed, the nuts of the bitter variety are
+sown, "in order that they may not be devoured by field-mice;"[568] so we
+see the use of the bitter principle in almonds.
+
+Other slight differences, which would be thought quite unimportant, are no
+doubt sometimes of great service both to plants and animals. The
+Whitesmith's gooseberry, as formerly stated, produces its leaves later than
+other varieties, and, as the flowers are thus left unprotected, the fruit
+often fails. In one variety of the cherry, according to Mr. Rivers,[569]
+the petals are much curled backwards, and in consequence of this the
+stigmas were observed to be killed by a severe frost; whilst at the same
+time, in another variety with incurved petals, the stigmas were not in the
+least injured. The straw of the Fenton wheat is remarkably unequal in
+height; and a competent observer believes that this variety is highly
+productive, partly because the ears, from being distributed at various
+heights above the ground, {233} are less crowded together. The same
+observer maintains that in the upright varieties the divergent awns are
+serviceable by breaking the shocks when the ears are dashed together by the
+wind.[570] If several varieties of a plant are grown together, and the seed
+is indiscriminately harvested, it is clear that the hardier and more
+productive kinds will, by a sort of natural selection, gradually prevail
+over the others; this takes place, as Colonel Le Couteur believes,[571] in
+our wheat-fields, for, as formerly shown, no variety is quite uniform in
+character. The same thing, as I am assured by nurserymen, would take place
+in our flower-gardens, if the seed of the different varieties were not
+separately saved. When the eggs of the wild and tame duck are hatched
+together, the young wild ducks almost invariably perish, from being of
+smaller size and not getting their fair share of food.[572]
+
+Facts in sufficient number have now been given showing that natural
+selection often checks, but occasionally favours, man's power of selection.
+These facts teach us, in addition, a valuable lesson, namely, that we ought
+to be extremely cautious in judging what characters are of importance in a
+state of nature to animals and plants, which have to struggle from the hour
+of their birth to that of their death for existence,--their existence
+depending on conditions, about which we are profoundly ignorant.
+
+_Circumstances favourable to Selection by Man._
+
+The possibility of selection rests on variability, and this, as we shall
+see in the following chapters, mainly depends on changed conditions of
+life, but is governed by infinitely complex, and, to a great extent,
+unknown laws. Domestication, even when long continued, occasionally causes
+but a small amount of variability, as in the case of the goose and turkey.
+The slight differences, however, which characterise each individual animal
+and plant would in most, probably in all cases, suffice for the production
+of distinct races through careful and prolonged selection. We see what
+selection, though acting on mere individual differences, can effect when
+families of cattle, sheep, {234} pigeons, &c., of the same race, have been
+separately bred during a number of years by different men without any wish
+on their part to modify the breed. We see the same fact in the difference
+between hounds bred for hunting in different districts,[573] and in many
+other such cases.
+
+In order that selection should produce any result, it is manifest that the
+crossing of distinct races must be prevented; hence facility in pairing, as
+with the pigeon, is highly favourable for the work; and difficulty in
+pairing, as with cats, prevents the formation of distinct breeds. On nearly
+the same principle the cattle of the small island of Jersey have been
+improved in their milking qualities "with a rapidity that could not have
+been obtained in a widely extended country like France."[574] Although free
+crossing is a danger on the one side which every one can see, too close
+interbreeding is a hidden danger on the other side. Unfavourable conditions
+of life overrule the power of selection. Our improved heavy breeds of
+cattle and sheep could not have been formed on mountainous pastures; nor
+could dray-horses have been raised on a barren and inhospitable land, such
+as the Falkland islands, where even the light horses of La Plata rapidly
+decrease in size. Nor could the wool of sheep have been much increased in
+length within the Tropics; yet selection has kept Merino sheep nearly true
+under diversified and unfavourable conditions of life. The power of
+selection is so great, that breeds of the dog, sheep, and poultry, of the
+largest and least size, long and short beaked pigeons, and other breeds
+with opposite characters, have had their characteristic qualities
+augmented, though treated in every way alike, being exposed to the same
+climate and fed on the same food. Selection, however, is either checked or
+favoured by the effects of use or habit. Our wonderfully-improved pigs
+could never have been formed if they had been forced to search for their
+own food; the English racehorse and greyhound could not have been improved
+up to their present high standard of excellence without constant training.
+
+As conspicuous deviations of structure occur rarely, the improvement of
+each breed is generally the result, as already {235} remarked, of the
+selection of slight individual differences. Hence the closest attention,
+the sharpest powers of observation, and indomitable perseverance, are
+indispensable. It is, also, highly important that many individuals of the
+breed which is to be improved should be raised; for thus there will be a
+better chance of the appearance of variations in the right direction, and
+individuals varying in an unfavourable manner may be freely rejected or
+destroyed. But that a large number of individuals should be raised, it is
+necessary that the conditions of life should favour the propagation of the
+species. Had the peacock been bred as easily as the fowl, we should
+probably ere this have had many distinct races. We see the importance of a
+large number of plants, from the fact of nursery gardeners almost always
+beating amateurs in the exhibition of new varieties. In 1845 it was
+estimated[575] that between 4000 and 5000 pelargoniums were annually raised
+from seed in England, yet a decidedly improved variety is rarely obtained.
+At Messrs. Carter's grounds, in Essex, where such flowers as the Lobelia,
+Nemophila, Mignonette, &c., are grown by the acre for seed, "scarcely a
+season passes without some new kinds being raised, or some improvement
+affected on old kinds."[576] At Kew, as Mr. Beaton remarks, where many
+seedlings of common plants are raised, "you see new forms of Laburnums,
+Spiraeas, and other shrubs."[577] So with animals: Marshall,[578] in
+speaking of the sheep in one part of Yorkshire, remarks, "as they belong to
+poor people, and are mostly in small lots, they never can be improved."
+Lord Rivers, when asked how he succeeded in always having first-rate
+greyhounds, answered, "I breed many, and hang many." This, as another man
+remarks, "was the secret of his success; and the same will be found in
+exhibiting fowls,--successful competitors breed largely, and keep the
+best."[579]
+
+It follows from this that the capacity of breeding at an early age and at
+short successive intervals, as with pigeons, rabbits, &c., facilitates
+selection; for the result is thus soon made visible, and perseverance in
+the work is encouraged. It can hardly be {236} accidental that the great
+majority of the culinary and agricultural plants which have yielded
+numerous races are annuals or biennials, which therefore are capable of
+rapid propagation and thus of improvement. Sea-kale, asparagus, common and
+Jerusalem artichokes, potatoes, and onions, alone are perennials. Onions
+are propagated like annuals, and of the other plants just specified, none,
+with the exception of the potato, have yielded more than one or two
+varieties. No doubt fruit-trees, which cannot be propagated quickly by
+seed, have yielded a host of varieties, though not permanent races; but
+these, judging from pre-historic remains, were produced at a later and more
+civilised epoch than the races of culinary and agricultural plants.
+
+A species may be highly variable, but distinct races will not be formed, if
+from any cause selection be not applied. The carp is highly variable, but
+it would be extremely difficult to select slight variations in fishes
+whilst living in their natural state, and distinct races have not been
+formed;[580] on the other hand, a closely allied species, the gold-fish,
+from being reared in glass or open vessels, and from having been carefully
+attended to by the Chinese, has yielded many races. Neither the bee, which
+has been semi-domesticated from an extremely remote period, nor the
+cochineal insect, which was cultivated by the aboriginal Mexicans, has
+yielded races; and it would be impossible to match the queen-bee with any
+particular drone, and most difficult to match cochineal insects.
+Silk-moths, on the other hand, have been subjected to rigorous selection,
+and have produced a host of races. Cats, which from their nocturnal habits
+cannot be selected for breeding, do not, as formerly remarked, yield
+distinct races in the same country. The ass in England varies much in
+colour and size; but it is an animal of little value, bred by poor people;
+consequently there has been no selection, and distinct races have not been
+formed. We must not attribute the inferiority of our asses to climate, for
+in India they are of even smaller size than in Europe. But when selection
+is brought to bear on the ass, all is changed. Near Cordova, as I am
+informed (Feb. 1860) by Mr. W. E. Webb, C.E., they are carefully bred, as
+much as 200l. having been paid for a stallion ass, {237} and they have been
+immensely improved. In Kentucky, asses have been imported (for breeding
+mules) from Spain, Malta, and France; these "seldom averaged more than
+fourteen hands high; but the Kentuckians, by great care, have raised them
+up to fifteen hands, and sometimes even to sixteen. The prices paid for
+these splendid animals, for such they really are, will prove how much they
+are in request. One male, of great celebrity, was sold for upwards of one
+thousand pounds sterling." These choice asses are sent to cattle-shows, one
+day being given to their exhibition.[581]
+
+Analogous facts have been observed with plants: the nutmeg-tree in the
+Malay archipelago is highly variable, but there has been no selection, and
+there are no distinct races.[582] The common mignonette (_Reseda odorata_),
+from bearing inconspicuous flowers, valued solely for their fragrance,
+"remains in the same unimproved condition as when first introduced."[583]
+Our common forest-trees are very variable, as may be seen in every
+extensive nursery-ground; but as they are not valued like fruit-trees, and
+as they seed late in life, no selection has been applied to them;
+consequently, as Mr. Patrick Matthews remarks,[584] they have not yielded
+distinct races, leafing at different periods, growing to different sizes,
+and producing timber fit for different purposes. We have gained only some
+fanciful and semi-monstrous varieties, which no doubt appeared suddenly as
+we now see them.
+
+Some botanists have argued that plants cannot have so strong a tendency to
+vary as is generally supposed, because many species long grown in botanic
+gardens, or unintentionally cultivated year after year mingled with our
+corn crops, have not produced distinct races; but this is accounted for by
+slight variations not having been selected and propagated. Let a plant
+which is now grown in a botanic garden, or any common weed, be cultivated
+on a large scale, and let a sharp-sighted gardener look out for each slight
+variety and sow the seed, and then, if distinct races are not produced, the
+argument will be valid.
+
+{238}
+
+The importance of selection is likewise shown by considering special
+characters. For instance, with most breeds of fowls the form of the comb
+and the colour of the plumage have been attended to, and are eminently
+characteristic of each race; but in Dorkings, fashion has never demanded
+uniformity of comb or colour; and the utmost diversity in these respects
+prevails. Rose-combs, double-combs, cup-combs, &c., and colours of all
+kinds, may be seen in purely-bred and closely related Dorking fowls, whilst
+other points, such as the general form of body, and the presence of an
+additional toe, have been attended to, and are invariably present. It has
+also been ascertained that colour can be fixed in this breed, as well as in
+any other.[585]
+
+       *       *       *       *       *
+
+During the formation or improvement of a breed, its members will always be
+found to vary much in those characters to which especial attention is
+directed, and of which each slight improvement is eagerly sought and
+selected. Thus with short-faced tumbler-pigeons, the shortness of the beak,
+shape of head and plumage,--with carriers, the length of the beak and
+wattle,--with fantails, the tail and carriage,--with Spanish fowls, the
+white face and comb,--with long-eared rabbits, the length of ear, are all
+points which are eminently variable. So it is in every case, and the large
+price paid for first-rate animals proves the difficulty of breeding them up
+to the highest standard of excellence. This subject has been discussed by
+fanciers,[586] and the greater prizes given for highly improved breeds, in
+comparison with those given for old breeds which are not now undergoing
+rapid improvement, has been fully justified. Nathusius makes[587] a similar
+remark when discussing the less uniform character of improved Shorthorn
+cattle and of the English horse, in comparison, for example, with the
+unennobled cattle of Hungary, or with the horses of the Asiatic steppes.
+This want of uniformity in the parts which at the time are undergoing
+selection, chiefly depends on the strength of the principle of reversion
+but it likewise depends to a certain extent on the continued {239}
+variability of the parts which have recently varied. That the same parts do
+continue varying in the same manner we must admit, for, if it were not so,
+there could be no improvement beyond an early standard of excellence, and
+we know that such improvement is not only possible, but is of general
+occurrence.
+
+As a consequence of continued variability, and more especially of
+reversion, all highly improved races, if neglected or not subjected to
+incessant selection, soon degenerate. Youatt gives a curious instance of
+this in some cattle formerly kept in Glamorganshire; but in this case the
+cattle were not fed with sufficient care. Mr. Baker, in his memoir on the
+Horse, sums up: "It must have been observed in the preceding pages that,
+whenever there has been neglect, the breed has proportionally
+deteriorated."[588] If a considerable number of improved cattle, sheep, or
+other animals of the same race, were allowed to breed freely together, with
+no selection, but with no change in their condition of life, there can be
+no doubt that after a score or hundred generations they would be very far
+from excellent of their kind; but, from what we see of the many common
+races of dogs, cattle, fowls, pigeons, &c., which without any particular
+care have long retained nearly the same character, we have no grounds for
+believing that they would altogether depart from their type.
+
+It is a general belief amongst breeders that characters of all kinds become
+fixed by long-continued inheritance. But I have attempted to show in the
+fourteenth chapter that this belief apparently resolves itself into the
+following proposition, namely, that all characters whatever, whether
+recently acquired or ancient, tend to be transmitted, but that those which
+have already long withstood all counteracting influences, will, as a
+general rule, continue to withstand them, and consequently be faithfully
+transmitted.
+
+_Tendency in Man to carry the practice of Selection to an extreme point._
+
+It is an important principle that in the process of selection man almost
+invariably wishes to go to an extreme point. Thus, in useful qualities,
+there is no limit to his desire to breed certain {240} horses and dogs as
+fleet as possible, and others as strong as possible; certain kinds of sheep
+for extreme fineness, and others for extreme length of wool; and he wishes
+to produce fruit, grain, tubers, and other useful parts of plants, as large
+and excellent as possible. With animals bred for amusement, the same
+principle is even more powerful; for fashion, as we see even in our dress,
+always runs to extremes. This view has been expressly admitted by fanciers.
+Instances were given in the chapters on the pigeon, but here is another:
+Mr. Eaton, after describing a comparatively new variety, namely, the
+Archangel, remarks, "What fanciers intend doing with this bird I am at a
+loss to know, whether they intend to breed it down to the tumbler's head
+and beak, or carry it out to the carrier's head and beak; leaving it as
+they found it, is not progressing." Ferguson, speaking of fowls, says,
+"their peculiarities, whatever they may be, must necessarily be fully
+developed: a little peculiarity forms nought but ugliness, seeing it
+violates the existing laws of symmetry." So Mr. Brent, in discussing the
+merits of the sub-varieties of the Belgian canary-bird, remarks, "Fanciers
+always go to extremes; they do not admire indefinite properties."[589]
+
+This principle, which necessarily leads to divergence of character,
+explains the present state of various domestic races. We can thus see how
+it is that race-horses and dray-horses, greyhounds and mastiffs, which are
+opposed to each other in every character,--how varieties so distinct as
+Cochin-China fowls and bantams, or carrier-pigeons with very long beaks,
+and tumblers with excessively short beaks, have been derived from the same
+stock. As each breed is slowly improved, the inferior varieties are first
+neglected and finally lost. In a few cases, by the aid of old records, or
+from intermediate varieties still existing in countries where other
+fashions have prevailed, we are enabled partially to trace the graduated
+changes through which certain breeds have passed. Selection, whether
+methodical or unconscious, always tending towards an extreme point,
+together with the neglect and slow extinction of the intermediate and
+less-valued forms, is the key which unlocks the mystery how man has
+produced such wonderful results.
+
+{241}
+
+In a few instances selection, guided by utility for a single purpose, has
+led to convergence of character. All the improved and different races of
+the pig, as Nathusius has well shown,[590] closely approach each other in
+character, in their shortened legs and muzzles, their almost hairless,
+large, rounded bodies, and small tusks. We see some degree of convergence
+in the similar outline of the body in well-bred cattle belonging to
+distinct races.[591] I know of no other such cases.
+
+Continued divergence of character depends on, and is indeed a clear proof,
+as previously remarked, of the same parts continuing to vary in the same
+direction. The tendency to mere general variability or plasticity of
+organisation can certainly be inherited, even from one parent, as has been
+shown by Gaertner and Koelreuter, in the production of varying hybrids from
+two species, of which one alone was variable. It is in itself probable
+that, when an organ has varied in any manner, it will again vary in the
+same manner, if the conditions which first caused the being to vary remain,
+as far as can be judged, the same. This is either tacitly or expressly
+admitted by all horticulturists: if a gardener observes one or two
+additional petals in a flower, he feels confident that in a few generations
+he will be able to raise a double flower, crowded with petals. Some of the
+seedlings from the weeping Moccas oak were so prostrate that they only
+crawled along the ground. A seedling from the fastigate or upright Irish
+yew is described as differing greatly from the parent-form "by the
+exaggeration of the fastigate habit of its branches."[592] Mr. Sheriff, who
+has been more successful than any other man in raising new kinds of wheat,
+remarks, "A good variety may safely be regarded as the forerunner of a
+better one."[593] A great rose-grower, Mr. Rivers, has made the same remark
+with respect to roses. Sageret,[594] who had large experience, in speaking
+of the future progress of fruit-trees, observes that the most important
+principle is "that the more plants have departed from their original type,
+the more they tend to depart from it." There is apparently much truth in
+this {242} remark; for we can in no other way understand the surprising
+amount of difference between varieties in the parts or qualities which are
+valued, whilst other parts retain nearly their original character.
+
+The foregoing discussion naturally leads to the question, what is the limit
+to the possible amount of variation in any part or quality, and,
+consequently, is there any limit to what selection can effect? Will a
+race-horse ever be reared fleeter than Eclipse? Can our prize-cattle and
+sheep be still further improved? Will a gooseberry ever weigh more than
+that produced by "London" in 1852? Will the beet-root in France yield a
+greater percentage of sugar? Will future varieties of wheat and other grain
+produce heavier crops than our present varieties? These questions cannot be
+positively answered; but it is certain that we ought to be cautious in
+answering by a negative. In some lines of variation the limit has probably
+been reached. Youatt believes that the reduction of bone in some of our
+sheep has already been carried so far that it entails great delicacy of
+constitution.[595] But seeing the great improvement within recent times in
+our cattle and sheep, and especially in our pigs; seeing the wonderful
+increase in weight in our poultry of all kinds during the last few years;
+he would be a bold man who would assert that perfection has been reached.
+Eclipse perhaps may never be beaten until all our race-horses have been
+rendered swifter, through the selection of the best horses during many
+generations; and then the old Eclipse may possibly be eclipsed; but, as Mr.
+Wallace has remarked, there must be an ultimate limit to the fleetness of
+every animal, whether under nature or domestication; and with the horse
+this limit has perhaps been reached. Until our fields are better manured,
+it may be impossible for a new variety of wheat to yield a heavier crop.
+But in many cases those who are best qualified to judge do not believe that
+the extreme point has as yet been reached even with respect to characters
+which have already been carried to a high standard of perfection. For
+instance, the short-faced tumbler-pigeon has been greatly modified;
+nevertheless, according to Mr. Eaton,[596] "the field is still as open for
+fresh competitors as it was one hundred years ago." Over and over again it
+has been said that {243} perfection had been attained with our flowers, but
+a higher standard has soon been reached. Hardly any fruit has been more
+improved than the strawberry, yet a great authority remarks,[597] "it must
+not be concealed that we are far from the extreme limits at which we may
+arrive."
+
+Time is an important element in the formation of our domestic races, as it
+permits innumerable individuals to be born, and these when exposed to
+diversified conditions are rendered variable. Methodical selection has been
+occasionally practised from an ancient period to the present day, even by
+semi-civilised people, and during former times will have produced some
+effect. Unconscious selection will have been still more effective; for
+during a lengthened period the more valuable individual animals will
+occasionally have been saved, and the less valuable neglected. In the
+course, also, of time, different varieties, especially in the less
+civilised countries, will have been more or less modified through natural
+selection. It is generally believed, though on this head we have little or
+no evidence, that new characters in time become fixed; and after having
+long remained fixed it seems possible that under new conditions they might
+again be rendered variable.
+
+How great the lapse of time has been since man first domesticated animals
+and cultivated plants, we begin dimly to see. When the lake-buildings of
+Switzerland were inhabited during the Neolithic period, several animals
+were already domesticated and various plants cultivated. If we may judge
+from what we now see of the habits of savages, it is probable that the men
+of the earlier Stone period--when many great quadrupeds were living which
+are now extinct, and when the face of the country was widely different from
+what it now is--possessed at least some few domesticated animals, although
+their remains have not as yet been discovered. If the science of language
+can be trusted, the art of ploughing and sowing the land was followed, and
+the chief animals had been already domesticated, at an epoch so immensely
+remote, that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavonic
+languages had not as yet diverged from their common parent-tongue.[598]
+
+{244}
+
+It is scarcely possible to overrate the effects of selection occasionally
+carried on in various ways and places during thousands of generations. All
+that we know, and, in a still stronger degree, all that we do not
+know,[599] of the history of the great majority of our breeds, even of our
+more modern breeds, agrees with the view that their production, through the
+action of unconscious and methodical selection, has been almost insensibly
+slow. When a man attends rather more closely than is usual to the breeding
+of his animals, he is almost sure to improve them to a slight extent. They
+are in consequence valued in his immediate neighbourhood, and are bred by
+others; and their characteristic features, whatever these may be, will then
+slowly but steadily be increased, sometimes by methodical and almost always
+by unconscious selection. At last a strain, deserving to be called a
+sub-variety, becomes a little more widely known, receives a local name, and
+spreads. The spreading will have been extremely slow during ancient and
+less civilised times, but now is rapid. By the time that the new breed had
+assumed a somewhat distinct character, its history, hardly noticed at the
+time, will have been completely forgotten; for, as Low remarks,[600] "we
+know how quickly the memory of such events is effaced."
+
+As soon as a new breed is thus formed, it is liable through the same
+process to break up into new strains and sub-varieties. For different
+varieties are suited for, and are valued under, different circumstances.
+Fashion changes, but, should a fashion last for even a moderate length of
+time, so strong is the principle of inheritance, that some effect will
+probably be impressed on the breed. Thus varieties go on increasing in
+number, and history shows us how wonderfully they have increased since the
+earliest records.[601] As each new variety is produced, the earlier,
+intermediate, and less valuable forms will be neglected, and perish. When a
+breed, from not being valued, is kept in small numbers, its extinction
+almost inevitably follows sooner or later, either from accidental causes of
+destruction or from close interbreeding; and this is an event which, in the
+case of well-marked breeds, excites attention. The birth or production of a
+new domestic race is so slow a process that it {245} escapes notice; its
+death or destruction is comparatively sudden, is often recorded, and when
+too late sometimes regretted.
+
+Several authors have drawn a wide distinction between artificial and
+natural races. The latter are more uniform in character, possessing in a
+high degree the character of natural species, and are of ancient origin.
+They are generally found in less civilised countries, and have probably
+been largely modified by natural selection, and only to a small extent by
+man's unconscious and methodical selection. They have, also, during a long
+period, been directly acted on by the physical conditions of the countries
+which they inhabit. The so-called artificial races, on the other hand, are
+not so uniform in character; some have a semi-monstrous character, such as
+"the wry-legged terriers so useful in rabbit-shooting,"[602] turnspit dogs,
+ancon sheep, niata oxen, Polish fowls, fantail-pigeons, &c.; their
+characteristic features have generally been acquired suddenly, though
+subsequently increased in many cases by careful selection. Other races,
+which certainly must be called artificial, for they have been largely
+modified by methodical selection and by crossing, as the English
+race-horse, terrier-dogs, the English game-cock, Antwerp carrier-pigeons,
+&c., nevertheless cannot be said to have an unnatural appearance; and no
+distinct line, as it seems to me, can be drawn between natural and
+artificial races.
+
+It is not surprising that domestic races should generally present a
+different aspect from natural species. Man selects and propagates
+modifications solely for his own use or fancy, and not for the creature's
+own good. His attention is struck by strongly marked modifications, which
+have appeared suddenly, due to some great disturbing cause in the
+organisation. He attends almost exclusively to external characters; and
+when he succeeds in modifying internal organs,--when for instance he
+reduces the bones and offal, or loads the viscera with fat, or gives early
+maturity, &c.,--the chances are strong that he will at the same time weaken
+the constitution. On the other hand, when an animal has to struggle
+throughout its life with many competitors and enemies, under circumstances
+inconceivably complex and liable to change, modifications of the most
+varied nature--in the internal organs as well as in external characters, in
+the {246} functions and mutual relations of parts--will be rigorously
+tested, preserved, or rejected. Natural selection often checks man's
+comparatively feeble and capricious attempts at improvement; and if this
+were not so, the result of his work, and of nature's work, would be even
+still more different. Nevertheless, we must not overrate the amount of
+difference between natural species and domestic races; the most experienced
+naturalists have often disputed whether the latter are descended from one
+or from several aboriginal stocks, and this clearly shows that there is no
+palpable difference between species and races.
+
+Domestic races propagate their kind far more truly, and endure for much
+longer periods, than most naturalists are willing to admit. Breeders feel
+no doubt on this head; ask a man who has long reared Shorthorn or Hereford
+cattle, Leicester or Southdown sheep, Spanish or Game poultry, tumbler or
+carrier-pigeons, whether these races may not have been derived from common
+progenitors, and he will probably laugh you to scorn. The breeder admits
+that he may hope to produce sheep with finer or longer wool and with better
+carcases, or handsomer fowls, or carrier-pigeons with beaks just
+perceptibly longer to the practised eye, and thus be successful at an
+exhibition. Thus far he will go, but no farther. He does not reflect on
+what follows from adding up during a long course of time many, slight,
+successive modifications; nor does he reflect on the former existence of
+numerous varieties, connecting the links in each divergent line of descent.
+He concludes, as was shown in the earlier chapters, that all the chief
+breeds to which he has long attended are aboriginal productions. The
+systematic naturalist, on the other hand, who generally knows nothing of
+the art of breeding, who does not pretend to know how and when the several
+domestic races were formed, who cannot have seen the intermediate
+gradations, for they do not now exist, nevertheless feels no doubt that
+these races are sprung from a single source. But ask him whether the
+closely allied natural species which he has studied may not have descended
+from a common progenitor, and he in his turn will perhaps reject the notion
+with scorn. Thus the naturalist and breeder may mutually learn a useful
+lesson from each other.
+
+       *       *       *       *       *
+
+_Summary on Selection by Man._--There can be no doubt that {247} methodical
+selection has effected and will effect wonderful results. It was
+occasionally practised in ancient times, and is still practised by
+semi-civilised people. Characters of the highest importance, and others of
+trifling value, have been attended to, and modified. I need not here repeat
+what has been so often said on the part which unconscious selection has
+played: we see its power in the difference between flocks which have been
+separately bred, and in the slow changes, as circumstances have slowly
+changed, which many animals have undergone in the same country, or when
+transported into a foreign land. We see the combined effects of methodical
+and unconscious selection in the great amount of difference between
+varieties in those parts or qualities which are valued by man, in
+comparison with those which are not valued, and consequently have not been
+attended to. Natural selection often determines man's power of selection.
+We sometimes err in imagining that characters, which are considered as
+unimportant by the systematic naturalist, could not be affected by the
+struggle for existence, and therefore be acted on by natural selection; but
+striking cases have been given, showing how great an error this is.
+
+The possibility of selection coming into action rests on variability; and
+this is mainly caused, as we shall hereafter see, by changes in the
+conditions of life. Selection is sometimes rendered difficult, or even
+impossible, by the conditions being opposed to the desired character or
+quality. It is sometimes checked by the lessened fertility and weakened
+constitution which follow from long-continued close interbreeding. That
+methodical selection may be successful, the closest attention and
+discernment, combined with unwearied patience, are absolutely necessary;
+and these same qualities, though not indispensable, are highly serviceable
+in the case of unconscious selection. It is almost necessary that a large
+number of individuals should be reared; for thus there will be a fair
+chance of variations of the desired nature arising, and every individual
+with the slightest blemish or in any degree inferior may be freely
+rejected. Hence length of time is an important element of success. Thus,
+also, propagation at an early age and at short intervals favours the work.
+Facility in pairing animals, or their inhabiting a confined area, is
+advantageous as a check to free crossing. Whenever and {248} wherever
+selection is not practised, distinct races are not formed. When any one
+part of the body or quality is not attended to, it remains either unchanged
+or varies in a fluctuating manner, whilst at the same time other parts and
+other qualities may become permanently and greatly modified. But from the
+tendency to reversion and to continued variability, those parts or organs
+which are now undergoing rapid improvement through selection, are likewise
+found to vary much. Consequently highly-bred animals, when neglected, soon
+degenerate; but we have no reason to believe that the effects of
+long-continued selection would, if the conditions of life remained the
+same, be soon and completely lost.
+
+Man always tends to go to an extreme point in the selection, whether
+methodical or unconscious, of all useful and pleasing qualities. This is an
+important principle, as it leads to continued divergence, and in some rare
+cases to convergence of character. The possibility of continued divergence
+rests on the tendency in each part or organ to go on varying in the same
+manner in which it has already varied; and that this occurs, is proved by
+the steady and gradual improvement of many animals and plants during
+lengthened periods. The principle of divergence of character, combined with
+the neglect and final extinction of all previous, less-valued, and
+intermediate varieties, explains the amount of difference and the
+distinctness of our several races. Although we may have reached the utmost
+limit to which certain characters can be modified, yet we are far from
+having reached, as we have good reason to believe, the limit in the
+majority of cases. Finally, from the difference between selection as
+carried on by man and by nature, we can understand how it is that domestic
+races often, though by no means always, differ in general aspect from
+closely allied natural species.
+
+Throughout this chapter and elsewhere I have spoken of selection as the
+paramount power, yet its action absolutely depends on what we in our
+ignorance call spontaneous or accidental variability. Let an architect be
+compelled to build an edifice with uncut stones, fallen from a precipice.
+The shape of each fragment may be called accidental; yet the shape of each
+has been determined by the force of gravity, the nature {249} of the rock,
+and the slope of the precipice,--events and circumstances, all of which
+depend on natural laws; but there is no relation between these laws and the
+purpose for which each fragment is used by the builder. In the same manner
+the variations of each creature are determined by fixed and immutable laws;
+but these bear no relation to the living structure which is slowly built up
+through the power of selection, whether this be natural or artificial
+selection.
+
+If our architect succeeded in rearing a noble edifice, using the rough
+wedge-shaped fragments for the arches, the longer stones for the lintels,
+and so forth, we should admire his skill even in a higher degree than if he
+had used stones shaped for the purpose. So it is with selection, whether
+applied by man or by nature; for though variability is indispensably
+necessary, yet, when we look at some highly complex and excellently adapted
+organism, variability sinks to a quite subordinate position in importance
+in comparison with selection, in the same manner as the shape of each
+fragment used by our supposed architect is unimportant in comparison with
+his skill.
+
+       *       *       *       *       *
+
+
+{250}
+
+CHAPTER XXII.
+
+CAUSES OF VARIABILITY.
+
+    VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES
+    ASSIGNED BY VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF
+    EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH
+    CHANGES--CLIMATE, FOOD, EXCESS OF NUTRIMENT--SLIGHT CHANGES
+    SUFFICIENT--EFFECTS OF GRAFTING ON THE VARIABILITY OF
+    SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO CHANGED
+    CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
+    INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
+    VARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW
+    CHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM
+    REVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH
+    EITHER DIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE
+    VARIABILITY.
+
+We will now consider, as far as we can, the causes of the almost universal
+variability of our domesticated productions. The subject is an obscure one;
+but it may be useful to probe our ignorance. Some authors, for instance Dr.
+Prosper Lucas, look at variability as a necessary contingent on
+reproduction, and as much an aboriginal law, as growth or inheritance.
+Others have of late encouraged, perhaps unintentionally, this view by
+speaking of inheritance and variability as equal and antagonistic
+principles. Pallas maintained, and he has had some followers, that
+variability depends exclusively on the crossing of primordially distinct
+forms. Other authors attribute the tendency to variability to an excess of
+food, and with animals to an excess relatively to the amount of exercise
+taken, or again to the effects of a more genial climate. That these causes
+are all effective is highly probable. But we must, I think, take a broader
+view, and conclude that organic beings, when subjected during several
+generations to any change whatever in their conditions, tend to vary; the
+kind of variation which ensues depending in a far higher degree on the
+nature or constitution of the being, than on the nature of the changed
+conditions. {251}
+
+Those authors who believe that it is a law of nature that each individual
+should differ in some slight degree from every other, may maintain,
+apparently with truth, that this is the fact, not only with all
+domesticated animals and cultivated plants, but likewise with all organic
+beings in a state of nature. The Laplander by long practice knows and gives
+a name to each reindeer, though, as Linnaeus remarks, "to distinguish one
+from another among such multitudes was beyond my comprehension, for they
+were like ants on an ant-hill." In Germany shepherds have won wagers by
+recognising each sheep in a flock of a hundred, which they had never seen
+until the previous fortnight. This power of discrimination, however, is as
+nothing compared to that which some florists have acquired. Verlot mentions
+a gardener who could distinguish 150 kinds of camellia, when not in flower;
+and it has been positively asserted that the famous old Dutch florist
+Voorhelm, who kept above 1200 varieties of the hyacinth, was hardly ever
+deceived in knowing each variety by the bulb alone. Hence we must conclude
+that the bulbs of the hyacinth and the branches and leaves of the camellia,
+though appearing to an unpractised eye absolutely undistinguishable, yet
+really differ.[603]
+
+As Linnaeus has compared the reindeer in number to ants, I may add that
+each ant knows its fellow of the same community. Several times I carried
+ants of the same species (_Formica rufa_) from one ant-hill to another,
+inhabited apparently by tens of thousands of ants; but the strangers were
+instantly detected and killed. I then put some ants taken from a very large
+nest into a bottle strongly perfumed with assafoetida, and after an
+interval of twenty-four hours returned them to their home; they were at
+first threatened by their fellows, but were soon recognised and allowed to
+pass. Hence each ant certainly recognises, independently of odour, its
+fellow; and if all the ants of the same community have not some countersign
+or watchword, they must present to each other's senses some distinguishable
+character.
+
+{252}
+
+The dissimilarity of brothers or sisters of the same family, and of
+seedlings from the same capsule, may be in part accounted for by the
+unequal blending of the characters of the two parents, and by the more or
+less complete recovery through reversion of ancestral characters on either
+side; but we thus only push the difficulty further back in time, for what
+made the parents or their progenitors different? Hence the belief[604] that
+an innate tendency to vary exists, independently of external conditions,
+seems at first sight probable. But even the seeds nurtured in the same
+capsule are not subjected to absolutely uniform conditions, as they draw
+their nourishment from different points; and we shall see in a future
+chapter that this difference sometimes suffices greatly to affect the
+character of the future plant. The less close similarity of the successive
+children of the same family in comparison with human twins, which often
+resemble each other in external appearance, mental disposition, and
+constitution, in so extraordinary a manner, apparently proves that the
+state of the parents at the exact period of conception, or the nature of
+the subsequent embryonic development, has a direct and powerful influence
+on the character of the offspring. Nevertheless, when we reflect on the
+{253} individual differences between organic beings in a state of nature,
+as shown by every wild animal knowing its mate; and when we reflect on the
+infinite diversity of the many varieties of our domesticated productions,
+we may well be inclined to exclaim, though falsely as I believe, that
+Variability must be looked at as an ultimate fact, necessarily contingent
+on reproduction.
+
+Those authors who adopt this latter view would probably deny that each
+separate variation has its own proper exciting cause. Although we can
+seldom trace the precise relation between cause and effect, yet the
+considerations presently to be given lead to the conclusion that each
+modification must have its own distinct cause. When we hear of an infant
+born, for instance, with a crooked finger, a misplaced tooth, or other
+slight deviation of structure, it is difficult to bring the conviction home
+to the mind that such abnormal cases are the result of fixed laws, and not
+of what we blindly call accident. Under this point of view the following
+case, which has been carefully examined and communicated to me by Dr.
+William Ogle, is highly instructive. Two girls, born as twins, and in all
+respects extremely alike, had their little fingers on both hands crooked;
+and in both children the second bicuspid tooth in the upper jaw, of the
+second dentition, was misplaced; for these teeth, instead of standing in a
+line with the others, grew from the roof of the mouth behind the first
+bicuspids. Neither the parents nor any other member of the family had
+exhibited any similar peculiarity. Now, as both these children were
+affected in exactly the same manner by both deviations of structure, the
+idea of accident is at once excluded; and we are compelled to admit that
+there must have existed some precise and sufficient cause which, if it had
+occurred a hundred times, would have affected a hundred children.
+
+We will now consider the general arguments, which appear to me to have
+great weight, in favour of the view that variations of all kinds and
+degrees are directly or indirectly caused by the conditions of life to
+which each being, and more especially its ancestors, have been exposed.
+
+No one doubts that domesticated productions are more variable than organic
+beings which have never been removed from their {254} natural conditions.
+Monstrosities graduate so insensibly into mere variations that it is
+impossible to separate them; and all those who have studied monstrosities
+believe that they are far commoner with domesticated than with wild animals
+and plants;[605] and in the case of plants, monstrosities would be equally
+noticeable in the natural as in the cultivated state. Under nature, the
+individuals of the same species are exposed to nearly uniform conditions,
+for they are rigorously kept to their proper places by a host of competing
+animals and plants; they have, also, long been habituated to their
+conditions of life; but it cannot be said that they are subject to quite
+uniform conditions, and they are liable to a certain amount of variation.
+The circumstances under which our domestic productions are reared are
+widely different: they are protected from competition; they have not only
+been removed from their natural conditions and often from their native
+land, but they are frequently carried from district to district, where they
+are treated differently, so that they never remain during a considerable
+length of time exposed to closely similar conditions. In conformity with
+this, all our domesticated productions, with the rarest exceptions, vary
+far more than natural species. The hive-bee, which feeds itself and follows
+in most respects its natural habits of life, is the least variable of all
+domesticated animals, and probably the goose is the next least variable;
+but even the goose varies more than almost any wild bird, so that it cannot
+be affiliated with perfect certainty to any natural species. Hardly a
+single plant can be named, which has long been cultivated and propagated by
+seed, that is not highly variable; common rye (_Secale cereale_) has
+afforded fewer and less marked varieties than almost any other cultivated
+plant;[606] but it may be doubted whether the variations of this, the least
+valuable of all our cereals, have been closely observed.
+
+Bud-variation, which was fully discussed in a former chapter, shows us that
+variability may be quite independent of seminal reproduction, and likewise
+of reversion to long-lost ancestral characters. No one will maintain that
+the sudden appearance {255} of a moss-rose on a Provence-rose is a return
+to a former state, for mossiness of the calyx has been observed in no
+natural species; the same argument is applicable to variegated and
+laciniated leaves; nor can the appearance of nectarines on peach-trees be
+accounted for with any probability on the principle of reversion. But
+bud-variations more immediately concern us, as they occur far more
+frequently on plants which have been highly cultivated during a length of
+time, than on other and less highly cultivated plants; and very few
+well-marked instances have been observed with plants growing under strictly
+natural conditions. I have given one instance of an ash-tree growing in a
+gentleman's pleasure-grounds; and occasionally there may be seen, on beech
+and other trees, twigs leafing at a different period from the other
+branches. But our forest trees in England can hardly be considered as
+living under strictly natural conditions; the seedlings are raised and
+protected in nursery-grounds, and must often be transplanted into places
+where wild trees of the kind would not naturally grow. It would be esteemed
+a prodigy if a dog-rose growing in a hedge produced by bud-variation a
+moss-rose, or a wild bullace or wild cherry-tree yielded a branch bearing
+fruit of a different shape and colour from the ordinary fruit. The prodigy
+would be enhanced if these varying branches were found capable of
+propagation, not only by grafts, but sometimes by seed; yet analogous cases
+have occurred with many of our highly cultivated trees and herbs.
+
+These several considerations alone render it probable that variability of
+every kind is directly or indirectly caused by changed conditions of life.
+Or, to put the case under another point of view, if it were possible to
+expose all the individuals of a species during many generations to
+absolutely uniform conditions of life, there would be no variability.
+
+_On the Nature of the Changes in the Conditions of Life which induce
+Variability._
+
+From a remote period to the present day, under climates and circumstances
+as different as it is possible to conceive, organic beings of all kinds,
+when domesticated or cultivated, have {256} varied. We see this with the
+many domestic races of quadrupeds and birds belonging to different orders,
+with gold-fish and silkworms, with plants of many kinds, raised in various
+quarters of the world. In the deserts of northern Africa the date-palm has
+yielded thirty-eight varieties; in the fertile plains of India it is
+notorious how many varieties of rice and of a host of other plants exist;
+in a single Polynesian island, twenty-four varieties of the bread-fruit,
+the same number of the banana, and twenty-two varieties of the arum, are
+cultivated by the natives; the mulberry-tree in India and Europe has
+yielded many varieties serving as food for the silkworm; and in China
+sixty-three varieties of the bamboo are used for various domestic
+purposes.[607] These facts alone, and innumerable others could be added,
+indicate that a change of almost any kind in the conditions of life
+suffices to cause variability--different changes acting on different
+organisms.
+
+Andrew Knight[608] attributed the variation of both animals and plants to a
+more abundant supply of nourishment, or to a more favourable climate, than
+that natural to the species. A more genial climate, however, is far from
+necessary; the kidney-bean, which is often injured by our spring frosts,
+and peaches, which require the protection of a wall, have varied much in
+England, as has the orange-tree in northern Italy, where it is barely able
+to exist.[609] Nor can we overlook the fact, though not immediately
+connected with our present subject, that the plants and shells of the
+arctic regions are eminently variable.[610] Moreover, it does not appear
+that a change of climate, whether more or less genial, is one of the most
+potent causes of variability; for in regard to plants Alph. De Candolle, in
+his 'Geographie {257} Botanique,' repeatedly shows that the native country
+of a plant, where in most cases it has been longest cultivated, is that
+where it has yielded the greatest number of varieties.
+
+It is doubtful whether a change in the nature of the food is a potent cause
+of variability. Scarcely any domesticated animal has varied more than the
+pigeon or the fowl, but their food, especially that of highly-bred pigeons,
+is generally the same. Nor can our cattle and sheep have been subjected to
+any great change in this respect. But in all these cases the food probably
+is much less varied in kind than that which was consumed by the species in
+its natural state.[611]
+
+Of all the causes which induce variability, excess of food, whether or not
+changed in nature, is probably the most powerful. This view was held with
+regard to plants by Andrew Knight, and is now held by Schleiden, more
+especially in reference to the inorganic elements of the food.[612] In
+order to give a plant more food it suffices in most cases to grow it
+separately, and thus prevent other plants robbing its roots. It is
+surprising, as I have often seen, how vigorously our common wild plants
+flourish when planted by themselves, though not in highly manured land.
+Growing plants separately is, in fact, the first step in cultivation. We
+see the converse of the belief that excess of food induces variability in
+the following statement by a great raiser of seeds of all kinds.[613] "It
+is a rule invariably with us, when we desire to keep a true stock of any
+one kind of seed, to grow it on poor land without dung; but when we grow
+for quantity, we act contrary, and sometimes have dearly to repent of it."
+
+In the case of animals the want of a proper amount of exercise, as
+Bechstein has remarked, has perhaps played, independently of the direct
+effects of the disuse of any particular organ, an important part in causing
+variability. We can see in a vague manner that, when the organised and
+nutrient fluids of the body are not used during growth, or by the wear and
+tear of the tissues, {258} they will be in excess; and as growth,
+nutrition, and reproduction are intimately allied processes, this
+superfluity might disturb the due and proper action of the reproductive
+organs, and consequently affect the character of the future offspring. But
+it may be argued that neither an excess of food nor a superfluity in the
+organised fluids of the body necessarily induces variability. The goose and
+the turkey have been well fed for many generations, yet have varied very
+little. Our fruit-trees and culinary plants, which are so variable, have
+been cultivated from an ancient period, and, though they probably still
+receive more nutriment than in their natural state, yet they must have
+received during many generations nearly the same amount; and it might be
+thought that they would have become habituated to the excess. Nevertheless,
+on the whole, Knight's view, that excess of food is one of the most potent
+causes of variability, appears, as far as I can judge, probable.
+
+Whether or not our various cultivated plants have received nutriment in
+excess, all have been exposed to changes of various kinds. Fruit-trees are
+grafted on different stocks, and grown in various soils. The seeds of
+culinary and agricultural plants are carried from place to place; and
+during the last century the rotation of our crops and the manures used have
+been greatly changed.
+
+Slight changes of treatment often suffice to induce variability. The simple
+fact of almost all our cultivated plants and domesticated animals having
+varied in all places and at all times, leads to this conclusion. Seeds
+taken from common English forest-trees, grown under their native climate,
+not highly manured or otherwise artificially treated, yield seedlings which
+vary much, as may be seen in every extensive seed-bed. I have shown in a
+former chapter what a number of well marked and singular varieties the
+thorn (_Crataegus oxyacantha_) has produced; yet this tree has been
+subjected to hardly any cultivation. In Staffordshire I carefully examined
+a large number of two British plants, namely, _Geranium phaeum_ and
+_Pyrenaicum_, which have never been highly cultivated. These plants had
+spread spontaneously by seed from a common garden into an open plantation;
+and the seedlings varied in almost every single character, both in their
+flowers and foliage, to a degree which {259} I have never seen exceeded;
+yet they could not have been exposed to any great change in their
+conditions.
+
+With respect to animals, Azara has remarked with much surprise,[614] that,
+whilst the feral horses on the Pampas are always of one of three colours,
+and the cattle always of a uniform colour, yet these animals, when bred on
+the unenclosed estancias, though kept in a state which can hardly be called
+domesticated, and apparently exposed to almost identically the same
+conditions as when they are feral, nevertheless display a great diversity
+of colour. So again in India several species of fresh-water fish are only
+so far treated artificially, that they are reared in great tanks; but this
+small change is sufficient to induce much variability.[615]
+
+Some facts on the effects of grafting, in regard to the variability of
+trees, deserve attention. Cabanis asserts that when certain pears are
+grafted on the quince, their seeds yield more varieties than do the seeds
+of the same variety of pear when grafted on the wild pear.[616] But as the
+pear and quince are distinct species, though so closely related that the
+one can be readily grafted and succeeds admirably on the other, the fact of
+variability being thus caused is not surprising; we are, however, here
+enabled to see the cause, namely, the different nature of the stock with
+its roots and the rest of the tree. Several North American varieties of the
+plum and peach are well known to reproduce themselves truly by seed; but
+Downing asserts,[617] "that when a graft is taken from one of these trees
+and placed upon another stock, this grafted tree is found to lose its
+singular property of producing the same variety by seed, and becomes like
+all other worked trees;"--that is, its seedlings become highly variable.
+Another case is worth giving: the Lalande variety of the walnut-tree leafs
+between April 20th and May 15th, and its seedlings invariably inherit the
+same habit; whilst several other varieties of the walnut leaf in June. Now,
+if seedlings are raised from the May-leafing Lalande variety, grafted on
+another May-leafing variety, though both stock and graft have the same
+early habit of leafing, yet the seedlings leaf at various times, {260} even
+as late as the 5th of June.[618] Such facts as these are well fitted to
+show, on what obscure and slight causes variability rests.
+
+    I may here just allude to the appearance of new and valuable varieties
+    of fruit-trees and of wheat in woods and waste places, which at first
+    sight seems a most anomalous circumstance. In France a considerable
+    number of the best pears have been discovered in woods; and this has
+    occurred so frequently, that Poiteau asserts that "improved varieties
+    of our cultivated fruits rarely originate with nurserymen."[619] In
+    England, on the other hand, no instance of a good pear having been
+    found wild has been recorded; and Mr. Rivers informs me that he knows
+    of only one instance with apples, namely, the Bess Poole, which was
+    discovered in a wood in Nottinghamshire. This difference between the
+    two countries may be in part accounted for by the more favourable
+    climate of France, but chiefly from the great number of seedlings which
+    spring up there in the woods. I infer that this is the case from a
+    remark made by a French gardener,[620] who regards it as a national
+    calamity that such a number of pear-trees are periodically cut down for
+    firewood, before they have borne fruit. The new varieties which thus
+    spring up in the woods, though they cannot have received any excess of
+    nutriment, will have been exposed to abruptly changed conditions, but
+    whether this is the cause of their production is very doubtful. These
+    varieties, however, are probably all descended[621] from old cultivated
+    kinds growing in adjoining orchards,--a circumstance which will account
+    for their variability; and out of a vast number of varying trees there
+    will always be a good chance of the appearance of a valuable kind. In
+    North America, where fruit-trees frequently spring up in waste places,
+    the Washington pear was found in a hedge, and the Emperor peach in a
+    wood.[622]
+
+    With respect to wheat, some writers have spoken[623] as if it were an
+    ordinary event for new varieties to be found in waste places; the
+    Fenton wheat was certainly discovered growing on a pile of basaltic
+    detritus in a quarry, but in such a situation the plant would probably
+    receive a sufficient amount {261} of nutriment. The Chidham wheat was
+    raised from an ear found _on_ a hedge; and Hunter's wheat was
+    discovered _by_ the roadside in Scotland, but it is not said that this
+    latter variety grew where it was found.[624]
+
+Whether our domestic productions would ever become so completely habituated
+to the conditions under which they now live, as to cease varying, we have
+no sufficient means for judging. But, in fact, our domestic productions are
+never exposed for a great length of time to uniform conditions, and it is
+certain that our most anciently cultivated plants, as well as animals,
+still go on varying, for all have recently undergone marked improvement. In
+some few cases, however, plants have become habituated to new conditions.
+Thus Metzger, who cultivated in Germany during many years numerous
+varieties of wheat, brought from different countries,[625] states that some
+kinds were at first extremely variable, but gradually, in one instance
+after an interval of twenty-five years, became constant; and it does not
+appear that this resulted from the selection of the more constant forms.
+
+       *       *       *       *       *
+
+_On the Accumulative Action of changed Conditions of Life._--We have good
+grounds for believing that the influence of changed conditions accumulates,
+so that no effect is produced on a species until it has been exposed during
+several generations to continued cultivation or domestication. Universal
+experience shows us that when new flowers are first introduced into our
+gardens they do not vary; but ultimately all, with the rarest exceptions,
+vary to a greater or less extent. In a few cases the requisite number of
+generations, as well as the successive steps in the progress of variation,
+have been recorded, as in the often-quoted instance of the Dahlia.[626]
+After several years' culture the Zinnia has only lately (1860) begun to
+vary in any great degree. "In the first seven or eight years of high
+cultivation the Swan River daisy (_Brachycome iberidifolia_) kept to its
+original colour; it then varied into lilac and purple and other minor
+shades."[627] Analogous facts have been recorded with the Scotch rose. In
+discussing the variability of plants several experienced horticulturists
+have spoken to the {262} same general effect. Mr. Salter[628] remarks,
+"Every one knows that the chief difficulty is in breaking through the
+original form and colour of the species, and every one will be on the
+look-out for any natural sport, either from seed or branch; that being once
+obtained, however trifling the change may be, the result depends upon
+himself." M. de Jonghe, who has had so much success in raising new
+varieties of pears and strawberries,[629] remarks with respect to the
+former, "There is another principle, namely, that the more a type has
+entered into a state of variation, the greater is its tendency to continue
+doing so; and the more it has varied from the original type, the more it is
+disposed to vary still farther." We have, indeed, already discussed this
+latter point when treating of the power which man possesses, through
+selection, of continually augmenting in the same direction each
+modification; for this power depends on continued variability of the same
+general kind. The most celebrated horticulturist in France, namely,
+Vilmorin,[630] even maintains that, when any particular variation is
+desired, the first step is to get the plant to vary in any manner whatever,
+and to go on selecting the most variable individuals, even though they vary
+in the wrong direction; for the fixed character of the species being once
+broken, the desired variation will sooner or later appear.
+
+As nearly all our animals were domesticated at an extremely remote epoch,
+we cannot, of course, say whether they varied quickly or slowly when first
+subjected to new conditions. But Dr. Bachman[631] states that he has seen
+turkeys raised from the eggs of the wild species lose their metallic tints
+and become spotted with white in the third generation. Mr. Yarrell many
+years ago informed me that the wild ducks bred on the ponds in St. James's
+Park, which had never been crossed, as it is believed, with domestic ducks,
+lost their true plumage after a few generations. An excellent
+observer,[632] who has often reared birds from the eggs of the wild duck,
+and who took precautions {263} that there should be no crossing with
+domestic breeds, has given, as previously stated, full details on the
+changes which they gradually undergo. He found that he could not breed
+these wild ducks true for more than five or six generations, "as they then
+proved so much less beautiful. The white collar round the neck of the
+mallard became much broader and more irregular, and white feathers appeared
+in the ducklings' wings." They increased also in size of body; their legs
+became less fine, and they lost their elegant carriage. Fresh eggs were
+then procured from wild birds; but again the same result followed. In these
+cases of the duck and turkey we see that animals, like plants, do not
+depart from their primitive type until they have been subjected during
+several generations to domestication. On the other hand, Mr. Yarrell
+informed me that the Australian dingos, bred in the Zoological Gardens,
+almost invariably produced in the first generation puppies marked with
+white and other colours; but these introduced dingos had probably been
+procured from the natives, who keep them in a semi-domesticated state. It
+is certainly a remarkable fact that changed conditions should at first
+produce, as far as we can see, absolutely no effect; but that they should
+subsequently cause the character of the species to change. In the chapter
+on pangenesis I shall attempt to throw a little light on this fact.
+
+       *       *       *       *       *
+
+Returning now to the causes which are supposed to induce variability. Some
+authors[633] believe that close interbreeding gives this tendency, and
+leads to the production of monstrosities. In the seventeenth chapter some
+few facts were advanced, showing that monstrosities are, as it appears,
+occasionally thus caused; and there can be no doubt that close
+interbreeding induces lessened fertility and a weakened constitution; hence
+it may lead to variability: but I have not sufficient evidence on this
+head. On the other hand, close interbreeding, if not carried to an
+injurious extreme, far from causing variability, tends to fix the character
+of each breed.
+
+It was formerly a common belief, still held by some persons, that the
+imagination of the mother affects the child in {264} the womb.[634] This
+view is evidently not applicable to the lower animals, which lay
+unimpregnated eggs, or to plants. Dr. William Hunter, in the last century,
+told my father that during many years every woman in a large London
+Lying-in Hospital was asked before her confinement whether anything had
+specially affected her mind, and the answer was written down; and it so
+happened that in no one instance could a coincidence be detected between
+the woman's answer and any abnormal structure; but when she knew the nature
+of the structure, she frequently suggested some fresh cause. The belief in
+the power of the mother's imagination may perhaps have arisen from the
+children of a second marriage resembling the previous father, as certainly
+sometimes occurs, in accordance with the facts given in the eleventh
+chapter.
+
+       *       *       *       *       *
+
+_Crossing as a Cause of Variability._--In an early part of this chapter it
+was stated that Pallas[635] and a few other naturalists maintain that
+variability is wholly due to crossing. If this means that new characters
+never spontaneously appear in our domestic races, but that they are all
+directly derived from certain aboriginal species, the doctrine is little
+less than absurd; for it implies that animals like Italian greyhounds,
+pug-dogs, bull-dogs, pouter and fantail pigeons, &c., were able to exist in
+a state of nature. But the doctrine may mean something widely different,
+namely, that the crossing of distinct species is the sole cause of the
+first appearance of new characters, and that without this aid man could not
+have formed his various breeds. As, however, new characters have appeared
+in certain cases by bud-variation, we may conclude with certainty that
+crossing is not necessary for variability. It is, moreover, almost certain
+that the breeds of various animals, such as of the rabbit, pigeon, duck,
+&c., and the varieties of several plants, are the modified descendants of a
+single wild species. Nevertheless, it is probable that the crossing of two
+forms, when one or both have long been domesticated or cultivated, adds to
+the variability of the offspring, independently of the commingling of the
+characters derived from the two parent-forms; and this implies {265} that
+new characters actually arise. But we must not forget the facts advanced in
+the thirteenth chapter, which clearly prove that the act of crossing often
+leads to the reappearance or reversion of long-lost characters; and in most
+cases it would be impossible to distinguish between the reappearance of
+ancient characters and the first appearance of new characters. Practically,
+whether new or old, they would be new to the breed in which they
+reappeared.
+
+    Gaertner declares,[636] and his experience is of the highest value on
+    such a point, that, when he crossed native plants which had not been
+    cultivated, he never once saw in the offspring any new character; but
+    that from the odd manner in which the characters derived from the
+    parents were combined, they sometimes appeared as if new. When, on the
+    other hand, he crossed cultivated plants, he admits that new characters
+    occasionally appeared, but he is strongly inclined to attribute their
+    appearance to ordinary variability, not in any way to the cross. An
+    opposite conclusion, however, appears to me the more probable.
+    According to Koelreuter, hybrids in the genus Mirabilis vary almost
+    infinitely, and he describes new and singular characters in the form of
+    the seeds, in the colour of the anthers, in the cotyledons being of
+    immense size, in new and highly peculiar odours, in the flowers
+    expanding early in the season, and in their closing at night. With
+    respect to one lot of these hybrids, he remarks that they presented
+    characters exactly the reverse of what might have been expected from
+    their parentage.[637]
+
+    Prof. Lecoq[638] speaks strongly to the same effect in regard to this
+    same genus, and asserts that many of the hybrids from _Mirabilis
+    jalapa_ and _multiflora_ might easily be mistaken for distinct species,
+    and adds that they differed in a greater degree, than the other species
+    of the genus, from _M. jalapa_. Herbert, also, has described[639] the
+    offspring from a hybrid Rhododendron as being "as _unlike all others_
+    in foliage, as if they had been a separate species." The common
+    experience of floriculturists proves that the crossing and recrossing
+    of distinct but allied plants, such as the species of Petunia,
+    Calceolaria, Fuchsia, Verbena, &c., induces excessive variability;
+    hence the appearance of quite new characters is probable. M.
+    Carriere[640] has lately discussed this subject: he states that
+    _Erythrina cristagalli_ had been multiplied by seed for many years, but
+    had not yielded any varieties: it was then crossed with the allied _E.
+    herbacea_, and "the resistance was now overcome, and varieties were
+    produced with flowers of extremely different size, form, and colour."
+
+    From the general and apparently well-founded belief that the crossing
+    {266} of distinct species, besides commingling their characters, adds
+    greatly to their variability, it has probably arisen that some
+    botanists have gone so far as to maintain[641] that, when a genus
+    includes only a single species, this when cultivated never varies. The
+    proposition made so broadly cannot be admitted; but it is probably true
+    that the variability of cultivated monotypic genera is much less than
+    that of genera including numerous species, and this quite independently
+    of the effects of crossing. I have stated in my 'Origin of Species,'
+    and in a future work shall more fully show, that the species belonging
+    to small genera generally yield a less number of varieties in a state
+    of nature than those belonging to large genera. Hence the species of
+    small genera would, it is probable, produce fewer varieties under
+    cultivation than the already variable species of larger genera.
+
+    Although we have not at present sufficient evidence that the crossing
+    of species, which have never been cultivated, leads to the appearance
+    of new characters, this apparently does occur with species which have
+    been already rendered in some degree variable through cultivation.
+    Hence crossing, like any other change in the conditions of life, seems
+    to be an element, probably a potent one, in causing variability. But we
+    seldom have the means of distinguishing, as previously remarked,
+    between the appearance of really new characters and the reappearance of
+    long-lost characters, evoked through the act of crossing. I will give
+    an instance of the difficulty in distinguishing such cases. The species
+    of Datura may be divided into two sections, those having white flowers
+    with green stems, and those having purple flowers with brown stems: now
+    Naudin[642] crossed _Datura laevis_ and _ferox_, both of which belong
+    to the white section, and raised from them 205 hybrids. Of these
+    hybrids, every one had brown stems and bore purple flowers; so that
+    they resembled the species of the other section of the genus, and not
+    their own two parents. Naudin was so much astonished at this fact, that
+    he was led carefully to observe both parent-species, and he discovered
+    that the pure seedlings of _D. ferox_, immediately after germination,
+    had dark purple stems, extending from the young roots up to the
+    cotyledons, and that this tint remained ever afterwards as a ring round
+    the base of the stem of the plant when old. Now I have shown in the
+    thirteenth chapter that the retention or exaggeration of an early
+    character is so intimately related to reversion, that it evidently
+    comes under the same principle. Hence probably we ought to look at the
+    purple flowers and brown stems of these hybrids, not as new characters
+    due to variability, but as a return to the former state of some ancient
+    progenitor.
+
+    Independently of the appearance of new characters from crossing, a few
+    words may be added to what has been said in former chapters on the
+    unequal combination and transmission of the characters proper to the
+    two parent-forms. When two species or races are crossed, the offspring
+    of {267} the first generation are generally uniform, but subsequently
+    they display an almost infinite diversity of character. He who wishes,
+    says Koelreuter,[643] to obtain an endless number of varieties from
+    hybrids should cross and recross them. There is also much variability
+    when hybrids or mongrels are reduced or absorbed by repeated crosses
+    with either pure parent-form; and a still higher degree of variability
+    when three distinct species, and most of all when four species, are
+    blended together by successive crosses. Beyond this point
+    Gaertner,[644] on whose authority the foregoing statements are made,
+    never succeeded in effecting a union; but Max Wichura[645] united six
+    distinct species of willows into a single hybrid. The sex of the
+    parent-species affects in an inexplicable manner the degree of
+    variability of hybrids; for Gaertner[646] repeatedly found that when a
+    hybrid was used as the father, and either one of the pure
+    parent-species, or a third species, was used as the mother, the
+    offspring were more variable than when the same hybrid was used as the
+    mother, and either pure parent or the same third species as the father:
+    thus seedlings from _Dianthus barbatus_ crossed by the hybrid _D.
+    chinensi-barbatus_ were more variable than those raised from this
+    latter hybrid fertilised by the pure _D. barbatus_. Max Wichura[647]
+    insists strongly on an analogous result with his hybrid willows. Again
+    Gaertner[648] asserts that the degree of variability sometimes differs
+    in hybrids raised from reciprocal crosses between the same two species;
+    and here the sole difference is, that the one species is first used as
+    the father and then as the mother. On the whole we see that,
+    independently of the appearance of new characters, the variability of
+    successive crossed generations is extremely complex, partly from the
+    offspring partaking unequally of the characters of the two
+    parent-forms, and more especially from their unequal tendency to revert
+    to these same characters or to those of more ancient progenitors.
+
+       *       *       *       *       *
+
+_On the Manner and on the Period of Action of the Causes which induce
+Variability._--This is an extremely obscure subject, and we need here only
+briefly consider, firstly, whether inherited variations are caused by the
+organisation being directly acted on, or indirectly through the
+reproductive system; and secondly, at what period of life or growth they
+are primarily caused. We shall see in the two following chapters that
+various agencies, such as an abundant supply of food, exposure to a
+different climate, increased use or disuse of parts, &c., prolonged during
+several generations, certainly modify either the whole organisation or
+certain organs. This direct action of changed conditions perhaps comes into
+play much more frequently than can be proved, and it is at least clear that
+in all cases of {268} bud-variation the action cannot have been through the
+reproductive system.
+
+    With respect to the part which the reproductive system takes in causing
+    variability, we have seen in the eighteenth chapter that even slight
+    changes in the conditions of life have a remarkable power in causing a
+    greater or less degree of sterility. Hence it seems not improbable that
+    being generated though a system so easily affected should themselves be
+    affected, or should fail to inherit, or inherit in excess, characters
+    proper to their parents. We know that certain groups of organic beings,
+    but with exceptions in each group, have their reproductive systems much
+    more easily affected by changed conditions than other groups; for
+    instance, carnivorous birds more readily than carnivorous mammals, and
+    parrots more readily than pigeons; and this fact harmonizes with the
+    apparently capricious manner and degree in which various groups of
+    animals and plants vary under domestication.
+
+    Koelreuter[649] was struck with the parallelism between the excessive
+    variability of hybrids when crossed and recrossed in various
+    ways,--these hybrids having their reproductive powers more or less
+    affected,--and the variability of anciently cultivated plants. Max
+    Wichura[650] has gone one step farther, and shows that with many of our
+    highly cultivated plants, such as the hyacinth, tulip, auricula,
+    snapdragon, potato, cabbage, &c., which there is no reason to believe
+    have been hybridized, the anthers contain many irregular pollen-grains,
+    in the same state as in hybrids. He finds also in certain wild forms,
+    the same coincidence between the state of the pollen and a high degree
+    of variability, as in many species of Rubus; but in _R. caesius_ and
+    _idaeus_, which are not highly variable species, the pollen is sound.
+    It is also notorious that many cultivated plants, such as the banana,
+    pine-apple, breadfruit, and others previously mentioned, have their
+    reproductive organs so seriously affected as to be generally quite
+    sterile; and when they do yield seed, the seedlings, judging from the
+    large number of cultivated races which exist, must be variable in an
+    extreme degree. These facts indicate that there is some relation
+    between the state of the reproductive organs and a tendency to
+    variability; but we must not conclude that the relation is strict.
+    Although many of our highly cultivated plants may have their pollen in
+    a deteriorated condition, yet, as we have previously seen, they yield
+    more seed, and our anciently domesticated animals are more prolific,
+    than the corresponding species in a state of nature. The peacock is
+    almost the only bird which is believed to be less fertile under
+    domestication than in its native state, and it has varied in a
+    remarkably small degree. From these considerations it would seem that
+    changes in the conditions of life lead either to sterility or to
+    variability, or to both; and not that sterility induces variability. On
+    the whole it is probable that any cause affecting the organs of
+    reproduction would likewise affect their product,--that is, the
+    offspring thus generated.
+
+    {269}
+
+    The period of life at which the causes that induce variability act, is
+    another obscure subject, which has been discussed by various
+    authors.[651] In some of the cases, to be given in the following
+    chapter, of modifications from the direct action of changed conditions,
+    which are inherited, there can be no doubt that the causes have acted
+    on the mature or nearly mature animal. On the other hand,
+    monstrosities, which cannot be distinctly separated from lesser
+    variations, are often caused by the embryo being injured whilst in the
+    mother's womb or in the egg. Thus I. Geoffroy St. Hilaire[652] asserts
+    that poor women who work hard during their pregnancy, and the mothers
+    of illegitimate children troubled in their minds and forced to conceal
+    their state, are far more liable to give birth to monsters than women
+    in easy circumstances. The eggs of the fowl when placed upright or
+    otherwise treated unnaturally frequently produce monstrous chickens. It
+    would, however, appear that complex monstrosities are induced more
+    frequently during a rather late than during a very early period of
+    embryonic life; but this may partly result from some one part, which
+    has been injured during an early period, affecting by its abnormal
+    growth other parts subsequently developed; and this would be less
+    likely to occur with parts injured at a later period.[653] When any
+    part or organ becomes monstrous through abortion, a rudiment is
+    generally left, and this likewise indicates that its development had
+    already commenced.
+
+    Insects sometimes have their antennae or legs in a monstrous condition,
+    and yet the larvae from which they are metamorphosed do not possess
+    either antennae or legs; and in those cases, as Quatrefages[654]
+    believes, we are enabled to see the precise period at which the normal
+    progress of development has been troubled. But the nature of the food
+    given to a caterpillar sometimes affects the colours of the moth,
+    without the caterpillar itself being affected; therefore it seems
+    possible that other characters in the mature insect might be indirectly
+    modified through the larvae. There is no reason to suppose that organs
+    which have been rendered monstrous have always been acted on during
+    their development; the cause may have acted on the organisation at a
+    much earlier stage. It is even probable that either the male or female
+    sexual elements, or both, before their union, may be affected in such a
+    manner as to lead to modifications in organs developed at a late period
+    of life; in nearly the same manner as a child may inherit from his
+    father a disease which does not appear until old age.
+
+    In accordance with the facts above given, which prove that in many
+    cases a close relation exists between variability and the sterility
+    following from changed conditions, we may conclude that the exciting
+    cause often acts at the earliest possible period, namely, on the sexual
+    elements, before impregnation has taken place. That an affection of the
+    female sexual element may induce variability we may likewise infer as
+    probable from the occurrence of bud-variations; for a bud seems to be
+    the analogue of an ovule. But the male element is apparently much
+    oftener affected by changed {270} conditions, at least in a visible
+    manner, than the female element or ovule; and we know from Gaertner's
+    and Wichura's statements that a hybrid used as the father and crossed
+    with a pure species gives a greater degree of variability to the
+    offspring, than does the same hybrid when used as the mother. Lastly,
+    it is certain that variability may be transmitted through either sexual
+    element, whether or not originally excited in them, for Koelreuter and
+    Gaertner[655] found that when two species were crossed, if either one
+    was variable, the offspring were rendered variable.
+
+       *       *       *       *       *
+
+_Summary._--From the facts given in this chapter, we may conclude that the
+variability of organic beings under domestication, although so general, is
+not an inevitable contingent on growth and reproduction, but results from
+the conditions to which the parents have been exposed. Changes of any kind
+in the conditions of life, even extremely slight changes, often suffice to
+cause variability. Excess of nutriment is perhaps the most efficient single
+exciting cause. Animals and plants continue to be variable for an immense
+period after their first domestication; but the conditions to which they
+are exposed never long remain quite constant. In the course of time they
+can be habituated to certain changes, so as to become less variable; and it
+is possible that when first domesticated they may have been even more
+variable than at present. There is good evidence that the power of changed
+conditions accumulates; so that two, three, or more generations must be
+exposed to new conditions before any effect is visible. The crossing of
+distinct forms, which have already become variable, increases in the
+offspring the tendency to further variability, by the unequal commingling
+of the characters of the two parents, by the reappearance of long-lost
+characters, and by the appearance of absolutely new characters. Some
+variations are induced by the direct action of the surrounding conditions
+on the whole organisation, or on certain parts alone, and other variations
+are induced indirectly through the reproductive system being affected in
+the same manner as is so common with organic beings when removed from their
+natural conditions. The causes which induce variability act on the mature
+organism, on the embryo, and, as we have good reason to believe, on both
+sexual elements before impregnation has been effected.
+
+       *       *       *       *       *
+
+
+{271}
+
+CHAPTER XXIII.
+
+DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.
+
+    SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
+    CONDITIONS IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF
+    THE TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED
+    CLIMATE OR FOOD, ETC.--PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT,
+    AND BY THE INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC
+    BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL
+    CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS
+    OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT
+    INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF
+    VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF
+    CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
+    UNNATURAL TREATMENT--SUMMARY.
+
+If we ask ourselves why this or that character has been modified under
+domestication, we are, in most cases lost in utter darkness. Many
+naturalists, especially of the French school, attribute every modification
+to the "monde ambiant," that is, to changed climate, with all its
+diversities of heat and cold, dampness and dryness, light and electricity,
+to the nature of the soil, and to varied kinds and amount of food. By the
+term definite action, as used in this chapter, I mean an action of such a
+nature that, when many individuals of the same variety are exposed during
+several generations to any change in their physical conditions of life,
+all, or nearly all the individuals, are modified in the same manner. A new
+sub-variety would thus be produced without the aid of selection.
+
+I do not include under the term of definite action the effects of habit or
+of the increased use and disuse of various organs. Modifications of this
+nature, no doubt, are definitely caused by the conditions to which the
+beings are subjected; but they depend much less on the nature of the
+conditions than on the laws of growth; hence they are included under a
+distinct head in the {272} following chapter. We know, however, far too
+little of the causes and laws of variation to make a sound classification.
+The direct action of the conditions of life, whether leading to definite or
+indefinite results, is a totally distinct consideration from the effects of
+natural selection; for natural selection depends on the survival under
+various and complex circumstances of the best-fitted individuals, but has
+no relation whatever to the primary cause of any modification of structure.
+
+I will first give in detail all the facts which I have been able to
+collect, rendering it probable that climate, food, &c., have acted so
+definitely and powerfully on the organisation of our domesticated
+productions, that they have sufficed to form new sub-varieties or races,
+without the aid of selection by man or of natural selection. I will then
+give the facts and considerations opposed to this conclusion, and finally
+we will weigh, as fairly as we can, the evidence on both sides.
+
+When we reflect that distinct races of almost all our domesticated animals
+exist in each kingdom of Europe, and formerly even in each district of
+England, we are at first strongly inclined to attribute their origin to the
+definite action of the physical conditions of each country; and this has
+been the conclusion of many authors. But we should bear in mind that man
+annually has to choose which animals shall be preserved for breeding, and
+which shall be slaughtered. We have also seen that both methodical and
+unconscious selection were formerly practised, and are now occasionally
+practised by the most barbarous races, to a much greater extent than might
+have been anticipated. Hence it is very difficult to judge how far the
+difference in conditions between, for instance, the several districts in
+England, could have sufficed without the aid of selection to modify the
+breeds which have been reared in each. It may be argued that, as numerous
+wild animals and plants have ranged during many ages throughout Great
+Britain, and still retain the same character, the difference in conditions
+between the several districts could not have modified in so marked a manner
+the various native races of cattle, sheep, pigs, and horses. The same
+difficulty of distinguishing between selection and the definite effects of
+the conditions of life, is encountered in a still higher degree when we
+compare closely allied natural {273} forms, inhabiting two countries, such
+as North America and Europe, which do not differ greatly in climate, nature
+of soil, &c., for in this case natural selection will inevitably and
+rigorously have acted during a long succession of ages.
+
+    From the importance of the difficulty just alluded to, it will be
+    advisable to give as large a body of facts as possible, showing that
+    extremely slight differences in treatment, either in different parts of
+    the same country, or during different seasons, certainly cause an
+    appreciable effect, at least on varieties which are already in an
+    unstable condition. Ornamental flowers are good for this purpose, as
+    they are highly variable, and are carefully observed. All
+    floriculturists are unanimous that certain varieties are affected by
+    very slight differences in the nature of the artificial compost in
+    which they are grown, and by the natural soil of the district, and by
+    the season. Thus, a skilful judge, in writing on Carnations and
+    Picotees,[656] asks "where can Admiral Curzon be seen possessing the
+    colour, size, and strength which it has in Derbyshire? Where can
+    Flora's Garland be found equal to those at Slough? Where do
+    high-coloured flowers revel better than at Woolwich and Birmingham? Yet
+    in no two of these districts do the same varieties attain an equal
+    degree of excellence, although each may be receiving the attention of
+    the most skilful cultivators." The same writer then recommends every
+    cultivator to keep five different kinds of soil and manure, "and to
+    endeavour to suit the respective appetites of the plants you are
+    dealing with, for without such attention all hope of general success
+    will be vain." So it is with the Dahlia:[657] the Lady Cooper rarely
+    succeeds near London, but does admirably in other districts; the
+    reverse holds good with other varieties; and again, there are others
+    which succeed equally well in various situations. A skilful
+    gardener[658] states that he procured cuttings of an old and well-known
+    variety (pulchella) of Verbena, which from having been propagated in a
+    different situation presented a slightly different shade of colour; the
+    two varieties were afterwards multiplied by cuttings, being carefully
+    kept distinct; but in the second year they could hardly be
+    distinguished, and in the third year no one could distinguish them.
+
+    The nature of the season has an especial influence on certain varieties
+    of the Dahlia: in 1841 two varieties were pre-eminently good, and the
+    next year these same two were pre-eminently bad. A famous amateur[659]
+    asserts that in 1861 many varieties of the Rose came so untrue in
+    character, "that it was hardly possible to recognise them, and the
+    thought was not seldom entertained that the grower had lost his tally."
+    The same amateur[660] states that in 1862 two-thirds of his Auriculas
+    produced central trusses of flowers, and these are remarkable from not
+    keeping true; {274} and he adds that in some seasons certain varieties
+    of this plant all prove good, and the next season all prove bad; whilst
+    exactly the reverse happens with other varieties. In 1845 the editor of
+    the 'Gardener's Chronicle'[661] remarked how singular it was that this
+    year many Calceolarias tended to assume a tubular form. With
+    Heartsease[662] the blotched sorts do not acquire their proper
+    character until hot weather sets in; whilst other varieties lose their
+    beautiful marks as soon as this occurs.
+
+    Analogous facts have been observed with leaves: Mr. Beaton asserts[663]
+    that he raised at Shrubland, during six years, twenty thousand
+    seedlings from the Punch Pelargonium, and not one had variegated
+    leaves; but at Surbiton, in Surrey, one-third, or even a greater
+    proportion, of the seedlings from this same variety were more or less
+    variegated. The soil of another district in Surrey has a strong
+    tendency to cause variegation, as appears from information given me by
+    Sir F. Pollock. Verlot[664] states that the variegated strawberry
+    retains its character as long as grown in a dryish soil, but soon loses
+    it when planted in fresh and humid soil. Mr. Salter, who is well known
+    for his success in cultivating variegated plants, informs me that rows
+    of strawberries were planted in his garden in 1859, in the usual way;
+    and at various distances in one row, several plants simultaneously
+    became variegated, and what made the case more extraordinary, all were
+    variegated in precisely the same manner. These plants were removed, but
+    during the three succeeding years other plants in the same row became
+    variegated, and in no instance were the plants in any adjoining row
+    affected.
+
+    The chemical qualities, odours, and tissues of plants are often
+    modified by a change which seems to us slight. The Hemlock is said not
+    to yield conicine in Scotland. The root of the _Aconitum napellus_
+    becomes innocuous in frigid climates. The medicinal properties of the
+    Digitalis are easily affected by culture. The Rhubarb flourishes in
+    England, but does not produce the medicinal substance which makes the
+    plant so valuable in Chinese Tartary. As the _Pistacia lentiscus_ grows
+    abundantly in the South of France, the climate must suit it, but it
+    yields no mastic. The _Laurus sassafras_ in Europe loses the odour
+    proper to it in North America.[665] Many similar facts could be given,
+    and they are remarkable because it might have been thought that
+    definite chemical compounds would have been little liable to change
+    either in quality or quantity.
+
+    The wood of the American Locust-tree (_Robinia_) when grown in England
+    is nearly worthless, as is that of the Oak-tree when grown at the Cape
+    of Good Hope.[666] Hemp and flax, as I hear from Dr. Falconer, flourish
+    and yield plenty of seed on the plains of India, but their fibres are
+    brittle {275} and useless. Hemp, on the other hand, fails to produce in
+    England that resinous matter which is so largely used in India as an
+    intoxicating drug.
+
+    The fruit of the Melon is greatly influenced by slight differences in
+    culture and climate. Hence it is generally a better plan, according to
+    Naudin, to improve an old kind than to introduce a new one into any
+    locality. The seed of the Persian Melon produces near Paris fruit
+    inferior to the poorest market kinds, but at Bordeaux yields delicious
+    fruit.[667] Seed is annually brought from Thibet to Kashmir,[668] and
+    produces fruit weighing from four to ten pounds, but plants raised from
+    seed saved in Kashmir next year give fruit weighing only from two to
+    three pounds. It is well known that American varieties of the Apple
+    produce in their native land magnificent and brightly-coloured fruit,
+    but in England of poor quality and a dull colour. In Hungary there are
+    many varieties of the Kidney-bean, remarkable for the beauty of their
+    seeds, but the Rev. M. J. Berkeley[669] found that their beauty could
+    hardly ever be preserved in England, and in some cases the colour was
+    greatly changed. We have seen in the ninth chapter, with respect to
+    wheat, what a remarkable effect transportal from the North to the South
+    of France, and reversely, produced on the weight of the grain.
+
+When man can perceive no change in plants or animals which have been
+exposed to a new climate or to different treatment, insects can sometimes
+perceive a marked change. The same species of cactus has been carried to
+India from Canton, Manilla, Mauritius, and from the hot-houses of Kew, and
+there is likewise a so-called native kind, formerly introduced from South
+America; all these plants are alike in appearance, but the cochineal insect
+flourishes only on the native kind, on which it thrives prodigiously.[670]
+Humboldt remarks[671] that white men "born in the torrid zone walk barefoot
+with impunity in the same apartment where a European, recently landed, is
+exposed to the attacks of the _Pulex penetrans_." This insect, the too
+well-known chigoe, must therefore be able to distinguish what the most
+delicate chemical analysis fails to distinguish, namely, a difference
+between the blood or tissues of a European and those of a white man born in
+the country. But the discernment of the chigoe is not so surprising as it
+at first appears; for {276} according to Liebig[672] the blood of men with
+different complexions, though inhabiting the same country, emits a
+different odour.
+
+    Diseases peculiar to certain localities, heights, or climates, may be
+    here briefly noticed, as showing the influence of external
+    circumstances on the human body. Diseases confined to certain races of
+    man do not concern us, for the constitution of the race may play the
+    more important part, and this may have been determined by unknown
+    causes. The Plica Polonica stands, in this respect, in a nearly
+    intermediate position; for it rarely affects Germans, who inhabit the
+    neighbourhood of the Vistula, where so many Poles are grievously
+    affected; and on the other hand, it does not affect Russians, who are
+    said to belong to the same original stock with the Poles.[673] The
+    elevation of a district often governs the appearance of diseases; in
+    Mexico the yellow fever does not extend above 924 metres; and in Peru,
+    people are affected with the _verugas_ only between 600 and 1600 metres
+    above the sea; many other such cases could be given. A peculiar
+    cutaneous complaint, called the _Bouton d'Alep_, affects in Aleppo and
+    some neighbouring districts almost every native infant, and some few
+    strangers; and it seems fairly well established that this singular
+    complaint depends on drinking certain waters. In the healthy little
+    island of St. Helena the scarlet-fever is dreaded like the Plague;
+    analogous facts have been observed in Chili and Mexico.[674] Even in
+    the different departments of France it is found that the various
+    infirmities which render the conscript unfit for serving in the army,
+    prevail with remarkable inequality, revealing, as Boudin observes, that
+    many of them are endemic, which otherwise would never have been
+    suspected.[675] Any one who will study the distribution of disease will
+    be struck with surprise at what slight differences in the surrounding
+    circumstances govern the nature and severity of the complaints by which
+    man is at least temporarily affected.
+
+The modifications as yet referred to have been extremely slight, and in
+most cases have been caused, as far as we can judge, by equally slight
+changes in the conditions. But can it be safely maintained that such
+changed conditions, if acting during a long series of generations, would
+not produce a marked effect? It is commonly believed that the people of the
+United States differ in appearance from the parent Anglo-Saxon race; and
+selection cannot have come into action within so short a period. A good
+observer[676] states that a general absence of fat, {277} a thin and
+elongated neck, stiff and lank hair, are the chief characteristics. The
+change in the nature of the hair is supposed to be caused by the dryness of
+the atmosphere. If immigration into the United States were now stopped, who
+can say that the character of the whole people would not be greatly
+modified in the course of two or three thousand years?
+
+    The direct and definite action of changed conditions, in
+    contradistinction to the accumulation of indefinite variations, seems
+    to me so important that I will give a large additional body of
+    miscellaneous facts. With plants, a considerable change of climate
+    sometimes produces a conspicuous result. I have given in detail in the
+    ninth chapter the most remarkable case known to me, namely, that in
+    Germany several varieties of maize brought from the hotter parts of
+    America were transformed in the course of only two or three
+    generations. Dr. Falconer informs me that he has seen the English
+    Ribston-pippin apple, a Himalayan oak, Prunus and Pyrus, all assume in
+    the hotter parts of India a fastigate or pyramidal habit; and this fact
+    is the more interesting, as a Chinese tropical species of Pyrus
+    naturally has this habit of growth. Although in these cases the changed
+    manner of growth seems to have been directly caused by the great heat,
+    we know that many fastigate trees have originated in their temperate
+    homes. In the Botanic Gardens of Ceylon the apple-tree[677] "sends out
+    numerous runners under ground, which continually rise into small stems,
+    and form a growth around the parent-tree." The varieties of the cabbage
+    which produce heads in Europe fail to do so in certain tropical
+    countries.[678] The _Rhododendron ciliatum_ produced at Kew flowers so
+    much larger and paler-coloured than those which it bears on its native
+    Himalayan mountain, that Dr. Hooker[679] would hardly have recognised
+    the species by the flowers alone. Many similar facts with respect to
+    the colour and size of flowers could be given.
+
+    The experiments of Vilmorin and Buckman on carrots and parsnips prove
+    that abundant nutriment produces a definite and inheritable effect on
+    the so-called roots, with scarcely any change in other parts of the
+    plant. Alum directly influences the colour of the flowers of the
+    Hydrangea.[680] Dryness seems generally to favour the hairyness or
+    villosity of plants. Gaertner found that hybrid Verbascums became
+    extremely woolly when grown in pots. Mr. Masters, on the other hand,
+    states that the _Opuntia leucotricha_ "is well clothed with beautiful
+    white hairs when grown in a damp heat; but in a dry heat exhibits none
+    of this peculiarity."[681] Slight variations of many kinds, not worth
+    specifying in detail, are retained only as {278} long as plants are
+    grown in certain soils, of which Sageret[682] gives from his own
+    experience some instances. Odart, who insists strongly on the
+    permanence of the varieties of the grape, admits[683] that some
+    varieties, when grown under a different climate or treated differently,
+    vary in an extremely slight degree, as in the tint of the fruit and in
+    the period of ripening. Some authors have denied that grafting causes
+    even the slightest difference in the scion; but there is sufficient
+    evidence that the fruit is sometimes slightly affected in size and
+    flavour, the leaves in duration, and the flowers in appearance.[684]
+
+    With animals there can be no doubt, from the facts given in the first
+    chapter, that European dogs deteriorate in India, not only in their
+    instincts but in structure; but the changes which they undergo are of
+    such a nature, that they may be partly due to reversion to a primitive
+    form, as in the case of feral animals. In parts of India the turkey
+    becomes reduced in size, "with the pendulous appendage over the beak
+    enormously developed."[685] We have seen how soon the wild duck, when
+    domesticated, loses its true character, from the effects of abundant or
+    changed food, or from taking little exercise. From the direct action of
+    a humid climate and poor pasture the horse rapidly decreases in size in
+    the Falkland Islands. From information which I have received, this
+    seems likewise to be the case to a certain extent with sheep in
+    Australia.
+
+    Climate definitely influences the hairy covering of animals; in the
+    West Indies a great change is produced in the fleece of sheep, in about
+    three generations. Dr. Falconer states[686] that the Thibet mastiff and
+    goat, when brought down from the Himalaya to Kashmir, lose their fine
+    wool. At Angora not only goats, but shepherd-dogs and cats, have fine
+    fleecy hair, and Mr. Ainsworth[687] attributes the thickness of the
+    fleece to the severe winters, and its silky lustre to the hot summers.
+    Burnes states positively[688] that the Karakool sheep lose their
+    peculiar black curled fleeces when removed into any other country. Even
+    within the limits of England, I have been assured that with two breeds
+    of sheep the wool was slightly changed by the flocks being pastured in
+    different localities.[689] It has been asserted on good authority[690]
+    that horses kept during several years in the deep coal-mines of Belgium
+    become covered with velvety hair, almost like that on the mole. These
+    cases probably stand in close relation to the natural change of coat in
+    winter and summer. Naked varieties of several domestic animals have
+    occasionally appeared; but there is no reason to {279} believe that
+    this is in any way related to the nature of the climate to which they
+    have been exposed.[691]
+
+    It appears at first sight probable that the increased size, the
+    tendency to fatten, the early maturity and altered forms of our
+    improved cattle, sheep, and pigs, have directly resulted from their
+    abundant supply of food. This is the opinion of many competent judges,
+    and probably is to a great extent true. But as far as form is
+    concerned, we must not overlook the equal or more potent influence of
+    lessened use on the limbs and lungs. We see, moreover, as far as size
+    is concerned, that selection is apparently a more powerful agent than a
+    large supply of food, for we can thus only account for the existence,
+    as remarked to me by Mr. Blyth, of the largest and smallest breeds of
+    sheep in the same country, of Cochin-China fowls and Bantams, of small
+    Tumbler and large Runt pigeons, all kept together and supplied with
+    abundant nourishment. Nevertheless there can be little doubt that our
+    domesticated animals have been modified, independently of the increased
+    or lessened use of parts, by the conditions to which they have been
+    subjected, without the aid of selection. For instance, Prof.
+    Ruetimeyer[692] shows that the bones of all domesticated quadrupeds can
+    be distinguished from those of wild animals by the state of their
+    surface and general appearance. It is scarcely possible to read
+    Nathusius's excellent 'Vorstudien,'[693] and doubt that, with the
+    highly improved races of the pig, abundant food has produced a
+    conspicuous effect on the general form of the body, on the breadth of
+    the head and face, and even on the teeth. Nathusius rests much on the
+    case of a purely bred Berkshire pig, which when two months old became
+    diseased in its digestive organs, and was preserved for observation
+    until nineteen months old; at this age it had lost several
+    characteristic features of the breed, and had acquired a long, narrow
+    head, of large size relatively to its small body, and elongated legs.
+    But in this case and in some others we ought not to assume that,
+    because certain characters are lost, perhaps through reversion, under
+    one course of treatment, therefore that they had been at first directly
+    produced by an opposite course.
+
+    In the case of the rabbit, which has become feral on the island of
+    Porto Santo, we are at first strongly tempted to attribute the whole
+    change--the greatly reduced size, the altered tints of the fur, and the
+    loss of certain characteristic marks--to the definite action of the new
+    conditions to which it has been exposed. But in all such cases we have
+    to consider in addition the tendency to reversion to progenitors more
+    or less remote, and the natural selection of the finest shades of
+    difference.
+
+    The nature of the food sometimes either definitely induces certain
+    peculiarities, or stands in some close relation with them. Pallas long
+    ago asserted that the fat-tailed sheep of Siberia degenerated and lost
+    their enormous tails when removed from certain saline pastures; and
+    recently {280} Erman[694] states that this occurs with the Kirgisian
+    sheep when brought to Orenburgh.
+
+    It is well known that hemp-seed causes bullfinches and certain other
+    birds to become black. Mr. Wallace has communicated to me some much
+    more remarkable facts of the same nature. The natives of the Amazonian
+    region feed the common green parrot (_Chrysotis festiva_, Linn.) with
+    the fat of large Siluroid fishes, and the birds thus treated become
+    beautifully variegated with red and yellow feathers. In the Malayan
+    archipelago, the natives of Gilolo alter in an analogous manner the
+    colours of another parrot, namely, the _Lorius garrulus_, Linn., and
+    thus produce the _Lori rajah_ or King-Lory. These parrots in the Malay
+    Islands and South America, when fed by the natives on natural vegetable
+    food, such as rice and plantains, retain their proper colours. Mr.
+    Wallace has, also, recorded[695] a still more singular fact. "The
+    Indians (of S. America) have a curious art by which they change the
+    colours of the feathers of many birds. They pluck out those from the
+    part they wish to paint, and inoculate the fresh wound with the milky
+    secretion from the skin of a small toad. The feathers grow of a
+    brilliant yellow colour, and on being plucked out, it is said, grow
+    again of the same colour without any fresh operation."
+
+    Bechstein[696] does not entertain any doubt that seclusion from light
+    affects, at least temporarily, the colours of cage-birds.
+
+    It is well known that the shells of land-mollusca are affected by the
+    abundance of lime in different districts. Isidore Geoffroy St.
+    Hilaire[697] gives the case of _Helix lactea_, which has recently been
+    carried from Spain to the South of France and to the Rio Plata, and in
+    both these countries now presents a distinct appearance, but whether
+    this has resulted from food or climate is not known. With respect to
+    the common oyster, Mr. F. Buckland informs me that he can generally
+    distinguish the shells from different districts; young oysters brought
+    from Wales and laid down in beds where "_natives_" are indigenous, in
+    the short space of two months begin to assume the "native" character.
+    M. Costa[698] has recorded a much more remarkable case of the same
+    nature, namely, that young shells taken from the shores of England and
+    placed in the Mediterranean, at once altered their manner of growth and
+    formed prominent diverging rays, like those on the shells of the proper
+    Mediterranean oyster. The same individual shell, showing both forms of
+    growth, was exhibited before a society in Paris. Lastly, it is well
+    known that caterpillars fed on different food sometimes either
+    themselves acquire a different colour or produce moths different in
+    colour.[699]
+
+    {281}
+
+    It would be travelling beyond my proper limits here to discuss how far
+    organic beings in a state of nature are definitely modified by changed
+    conditions. In my 'Origin of Species' I have given a brief abstract of
+    the facts bearing on this point, and have shown the influence of light
+    on the colours of birds, and of residence near the sea on the lurid
+    tints of insects, and on the succulency of plants. Mr. Herbert
+    Spencer[700] has recently discussed with much ability this whole
+    subject on broad and general grounds. He argues, for instance, that
+    with all animals the external and internal tissues are differently
+    acted on by the surrounding conditions, and they invariably differ in
+    intimate structure. So again the upper and lower surfaces of true
+    leaves, as well as of stems and petioles, when these assume the
+    function and occupy the position of leaves, are differently
+    circumstanced with respect to light, &c., and apparently in consequence
+    differ in structure. But, as Mr. Herbert Spencer admits, it is most
+    difficult in all such cases to distinguish between the effects of the
+    definite action of physical conditions and the accumulation through
+    natural selection of inherited variations which are serviceable to the
+    organism, and which have arisen independently of the definite action of
+    these conditions.
+
+Although we are not here concerned with organic beings in a state of
+nature, yet I may call attention to one case. Mr. Meehan,[701] in a
+remarkable paper, compares twenty-nine kinds of American trees, belonging
+to various orders, with their nearest European allies, all grown in close
+proximity in the same garden and under as nearly as possible the same
+conditions. In the American species Mr. Meehan finds, with the rarest
+exceptions, that the leaves fall earlier in the season, and assume before
+falling a brighter tint; that they are less deeply toothed or serrated;
+that the buds are smaller; that the trees are more diffuse in growth and
+have fewer branchlets; and, lastly, that the seeds are smaller--all in
+comparison with the corresponding European species. Now, considering that
+these trees belong to distinct orders, it is out of the question that the
+peculiarities just specified should have been inherited in the one
+continent from one progenitor, and in the other from another progenitor;
+and considering that the trees inhabit widely different stations, these
+peculiarities can hardly be supposed to be of any special {282} service to
+the two series in the Old and New Worlds; therefore these peculiarities
+cannot have been naturally selected. Hence we are led to infer that they
+have been definitely caused by the long-continued action of the different
+climate of the two continents on the trees.
+
+_Galls._--Another class of facts, not relating to cultivated plants,
+deserves attention. I allude to the production of galls. Every one knows
+the curious, bright-red, hairy productions on the wild rose-tree, and the
+various different galls produced by the oak. Some of the latter resemble
+fruit, with one face as rosy as the rosiest apple. These bright colours can
+be of no service either to the gall-forming insect or to the tree, and
+probably are the direct result of the action of the light, in the same
+manner as the apples of Nova Scotia or Canada are brighter coloured than
+English apples. The strongest upholder of the doctrine that organic beings
+are created beautiful to please mankind would not, I presume, extend this
+view to galls. According to Osten Sacken's latest revision, no less than
+fifty-eight kinds of galls are produced on the several species of oak, by
+Cynips with its sub-genera; and Mr. B. D. Walsh[702] states that he can add
+many others to the list. One American species of willow, the _Salix
+humilis_, bears ten distinct kinds of galls. The leaves which spring from
+the galls of various English willows differ completely in shape from the
+natural leaves. The young shoots of junipers and firs, when punctured by
+certain insects, yield monstrous growths like flowers and cones; and the
+flowers of some plants become from the same cause wholly changed in
+appearance. Galls are produced in every quarter of the world; of several
+sent to me by Mr. Thwaites from Ceylon, some were as symmetrical as a
+composite flower when in bud, others smooth and spherical like a berry;
+some protected by long spines, others clothed with yellow wool formed of
+long cellular hairs, others with regularly tufted hairs. In some galls the
+internal structure is simple, but in others it is highly complex; thus M.
+Lucaze-Duthiers[703] has figured in the common ink-gall no less than seven
+concentric layers, composed of distinct tissue, {283} namely, the
+epidermic, sub-epidermic, spongy, intermediate, and the hard protective
+layer formed of curiously thickened woody cells, and, lastly, the central
+mass abounding with starch-granules on which the larvae feed.
+
+Galls are produced by insects of various orders, but the greater number by
+species of Cynips. It is impossible to read M. Lucaze-Duthier's discussion
+and doubt that the poisonous secretion of the insect causes the growth of
+the gall, and every one knows how virulent is the poison secreted by wasps
+and bees, which belong to the same order with Cynips. Galls grow with
+extraordinary rapidity, and it is said that they attain their full size in
+a few days;[704] it is certain that they are almost completely developed
+before the larvae are hatched. Considering that many gall-insects are
+extremely small, the drop of secreted poison must be excessively minute; it
+probably acts on one or two cells alone, which, being abnormally
+stimulated, rapidly increase by a process of self-division. Galls, as Mr.
+Walsh[705] remarks, afford good, constant, and definite characters, each
+kind keeping as true to form as does any independent organic being. This
+fact becomes still more remarkable when we hear that, for instance, seven
+out of the ten different kinds of galls produced on _Salix humilis_ are
+formed by gall-gnats (_Cecidomyidae_) which, "though essentially distinct
+species, yet resemble one another so closely that in almost all cases it is
+difficult, and in some cases impossible, to distinguish the full-grown
+insects one from the other."[706] For in accordance with a wide-spread
+analogy we may safely infer that the poison secreted by insects so closely
+allied would not differ much in nature; yet this slight difference is
+sufficient to induce widely different results. In some few cases the same
+species of gall-gnat produces on distinct species of willows galls which
+cannot be distinguished; the _Cynips fecundatrix_, also, has been known to
+produce on the Turkish oak, to which it is not properly attached, exactly
+the same kind of gall as on the European oak.[707] These latter facts
+apparently prove that the nature of the poison is a much more powerful
+{284} agent in determining the form of the gall than the specific character
+of the tree which is acted on.
+
+As the poisonous secretion of insects belonging to various orders has the
+special power of affecting the growth of various plants;--as a slight
+difference in the nature of the poison suffices to produce widely different
+results;--and lastly, as we know that the chemical compounds secreted by
+plants are eminently liable to be modified by changed conditions of life,
+we may believe it possible that various parts of a plant might be modified
+through the agency of its own altered secretions. Compare, for instance,
+the mossy and viscid calyx of a moss-rose, which suddenly appears through
+bud-variation on a Provence-rose, with the gall of red moss growing from
+the inoculated leaf of a wild rose, with each filament symmetrically
+branched like a microscopical spruce-fir, bearing a glandular tip and
+secreting odoriferous gummy matter.[708] Or compare, on the one hand, the
+fruit of the peach, with its hairy skin, fleshy covering, hard shell and
+kernel, and on the other hand one of the more complex galls with its
+epidermic, spongy, and woody layers, surrounding tissue loaded with starch
+granules. These normal and abnormal structures manifestly present a certain
+degree of resemblance. Or, again, reflect on the cases above given of
+parrots which have had their plumage brightly decorated through some change
+in their blood, caused by having been fed on certain fishes, or locally
+inoculated with the poison of a toad. I am far from wishing to maintain
+that the moss-rose or the hard shell of the peach-stone or the bright
+colours of birds are actually due to any chemical change in the sap or
+blood; but these cases of galls and of parrots are excellently adapted to
+show us how powerfully and singularly external agencies may affect
+structure. With such facts before us, we need feel no surprise at the
+appearance of any modification in any organic being.
+
+    I may, also, here allude to the remarkable effects which parasitic
+    fungi sometimes produce on plants. Reissek[709] has described a
+    Thesium, affected by an Oecidium, which was greatly modified, and
+    assumed some of the {285} characteristic features of certain allied
+    species, or even genera. Suppose, says Reissek, "the condition
+    originally caused by the fungus to become constant in the course of
+    time, the plant would, if found growing wild, be considered as a
+    distinct species or even as belonging to a new genus." I quote this
+    remark to show how profoundly, yet in how natural a manner, this plant
+    must have been modified by the parasitic fungus.
+
+_Facts and Considerations opposed to the belief that the Conditions of Life
+act in a potent manner in causing definite Modifications of Structure._
+
+I have alluded to the slight differences in species when naturally living
+in distinct countries under different conditions; and such differences we
+feel at first inclined, probably to a limited extent with justice, to
+attribute to the definite action of the surrounding conditions. But it must
+be borne in mind that there are a far greater number of animals and plants
+which range widely and have been exposed to great diversities of
+conditions, yet remain nearly uniform in character. Some authors, as
+previously remarked, account for the varieties of our culinary and
+agricultural plants by the definite action of the conditions to which they
+have been exposed in the different parts of Great Britain; but there are
+about 200 plants[710] which are found in every single English county; these
+plants must have been exposed for an immense period to considerable
+differences of climate and soil, yet do not differ. So, again, some birds,
+insects, other animals, and plants range over large portions of the world,
+yet retain the same character.
+
+    Notwithstanding the facts previously given on the occurrence of highly
+    peculiar local diseases and on the strange modifications of structure
+    in plants caused by the inoculated poison of insects, and other
+    analogous cases; still there are a multitude of variations--such as the
+    modified skull of the niata ox and bulldog, the long horns of Caffre
+    cattle, the conjoined toes of the solid-hoofed swine, the immense crest
+    and protuberant skull of Polish fowls, the crop of the pouter-pigeon,
+    and a host of other such cases--which we can hardly attribute to the
+    definite action, in the sense before specified, of the external
+    conditions of life. No doubt in every case there must have been some
+    exciting cause; but as we see innumerable individuals exposed to nearly
+    the same conditions, and one alone is affected, we may conclude that
+    the constitution of the individual is of far higher {286} importance
+    than the conditions to which it has been exposed. It seems, indeed, to
+    be a general rule that conspicuous variations occur rarely, and in one
+    individual alone out of many thousands, though all may have been
+    exposed, as far as we can judge, to nearly the same conditions. As the
+    most strongly marked variations graduate insensibly into the most
+    trifling, we are led by the same train of thought to attribute each
+    slight variation much more to innate differences of constitution,
+    however caused, than to the definite action of the surrounding
+    conditions.
+
+    We are led to the same conclusion by considering the cases, formerly
+    alluded to, of fowls and pigeons, which have varied and will no doubt
+    go on varying in directly opposite ways, though kept during many
+    generations under nearly the same conditions. Some, for instance, are
+    born with their beaks, wings, tails, legs, &c., a little longer, and
+    others with these same parts a little shorter. By the long-continued
+    selection of such slight individual differences, which occur in birds
+    kept in the same aviary, widely different races could certainly be
+    formed; and long-continued selection, important as is the result, does
+    nothing but preserve the variations which appear to us to arise
+    spontaneously.
+
+    In these cases we see that domesticated animals vary in an indefinite
+    number of particulars, though treated as uniformly as is possible. On
+    the other hand, there are instances of animals and plants, which,
+    though exposed to very different conditions, both under nature and
+    domestication, have varied in nearly the same manner. Mr. Layard
+    informs me that he has observed amongst the Caffres of South Africa a
+    dog singularly like an arctic Esquimaux dog. Pigeons in India present
+    nearly the same wide diversities of colour as in Europe; and I have
+    seen chequered and simply barred pigeons, and pigeons with blue and
+    white loins, from Sierra Leone, Madeira, England, and India. New
+    varieties of flowers are continually raised in different parts of Great
+    Britain, but many of these are found by the judges at our exhibitions
+    to be almost identical with old varieties. A vast number of new
+    fruit-trees and culinary vegetables have been produced in North
+    America: these differ from European varieties in the same general
+    manner as the several varieties raised in Europe differ from each
+    other; and no one has ever pretended that the climate of America has
+    given to the many American varieties any general character by which
+    they can be recognised. Nevertheless, from the facts previously
+    advanced on the authority of Mr. Meehan with respect to American and
+    European forest-trees, it would be rash to affirm that varieties raised
+    in the two countries would not in the course of ages assume a
+    distinctive character. Mr. Masters has recorded a striking fact[711]
+    bearing on this subject: he raised numerous plants of _Hybiscus
+    Syriacus_ from seed collected in South Carolina and the Holy Land,
+    where the parent-plants must have been exposed to considerably
+    different conditions; yet the seedlings from both localities broke into
+    two similar strains, one with obtuse leaves and purple or crimson
+    flowers, and the other with elongated leaves and more or less pink
+    flowers.
+
+    {287}
+
+    We may, also, infer the prepotent influence of the constitution of the
+    organism over the definite action of the conditions of life, from the
+    several cases given in the earlier chapters of parallel series of
+    varieties,--an important subject, hereafter to be more fully discussed.
+    Sub-varieties of the several kinds of wheat, gourds, peaches, and other
+    plants, and to a certain limited extent sub-varieties of the fowl,
+    pigeon, and dog, have been shown either to resemble or to differ from
+    each other in a closely corresponding and parallel manner. In other
+    cases, a variety of one species resembles a distinct species; or the
+    varieties of two distinct species resemble each other. Although these
+    parallel resemblances no doubt often result from reversion to the
+    former characters of a common progenitor; yet in other cases, when new
+    characters first appear, the resemblance must be attributed to the
+    inheritance of a similar constitution, and consequently to a tendency
+    to vary in the same manner. We see something of a similar kind in the
+    same monstrosity appearing and reappearing many times in the same
+    animal, and, as Dr. Maxwell Masters has remarked to me, in the same
+    plant.
+
+We may at least conclude thus far, that the amount of modification which
+animals and plants have undergone under domestication, does not correspond
+with the degree to which they have been subjected to changed circumstances.
+As we know the parentage of domesticated birds far better than of most
+quadrupeds, we will glance through the list. The pigeon has varied in
+Europe more than almost any other bird; yet it is a native species, and has
+not been exposed to any extraordinary change of conditions. The fowl has
+varied equally, or almost equally, with the pigeon, and is a native of the
+hot jungles of India. Neither the peacock, a native of the same country,
+nor the guinea-fowl, an inhabitant of the dry deserts of Africa, has varied
+at all, or only in colour. The turkey, from Mexico, has varied but little.
+The duck, on the other hand, a native of Europe, has yielded some
+well-marked races; and as this is an aquatic bird, it must have been
+subjected to a far more serious change in its habits than the pigeon or
+even the fowl, which nevertheless have varied in a much higher degree. The
+goose, a native of Europe and aquatic like the duck, has varied less than
+any other domesticated bird, except the peacock.
+
+Bud-variation is, also, important under our present point of view. In some
+few cases, as when all the eyes or buds on the same tuber of the potato, or
+all the fruit on the same plum-tree, or all the flowers on the same plant,
+have suddenly varied in the same manner, it might be argued that the {288}
+variation had been definitely caused by some change in the conditions to
+which the plants had been exposed; yet, in other cases, such an admission
+is extremely difficult. As new characters sometimes appear by
+bud-variation, which do not occur in the parent-species or in any allied
+species, we may reject, at least in these cases, the idea that they are due
+to reversion. Now it is well worth while to reflect maturely on some
+striking case of bud-variation, for instance that of the peach. This tree
+has been cultivated by the million in various parts of the world, has been
+treated differently, grown on its own roots and grafted on various stocks,
+planted as a standard, against a wall, and under glass; yet each bud of
+each sub-variety keeps true to its kind. But occasionally, at long
+intervals of time, a tree in England, or under the widely-different climate
+of Virginia, produces a single bud, and this yields a branch which ever
+afterwards bears nectarines. Nectarines differ, as every one knows, from
+peaches in their smoothness, size, and flavour; and the difference is so
+great, that some botanists have maintained that they are specifically
+distinct. So permanent are the characters thus suddenly acquired, that a
+nectarine produced by bud-variation has propagated itself by seed. To guard
+against the supposition that there is some fundamental distinction between
+bud and seminal variation, it is well to bear in mind that nectarines have
+likewise been produced from the stone of the peach; and, reversely, peaches
+from the stone of the nectarine. Now is it possible to conceive external
+conditions more closely alike than those to which the buds on the same tree
+are exposed? Yet one bud alone, out of the many thousands borne by the same
+tree, has suddenly without any apparent cause produced a nectarine. But the
+case is even stronger than this, for the same flower-bud has yielded a
+fruit, one-half or one-quarter a nectarine, and the other half or
+three-quarters a peach. Again, seven or eight varieties of the peach have
+yielded by bud-variation nectarines: the nectarines thus produced, no
+doubt, differ a little from each other; but still they are nectarines. Of
+course there must be some cause, internal or external, to excite the
+peach-bud to change its nature; but I cannot imagine a class of facts
+better adapted to force on our minds the conviction that what we call the
+external conditions of life are quite insignificant in {289} relation to
+any particular variation, in comparison with the organisation or
+constitution of the being which varies.
+
+It is known from the labours of Geoffroy St. Hilaire, and recently from
+those of Dareste and others, that eggs of the fowl, if shaken, placed
+upright, perforated, covered in part with varnish, &c., produce monstrous
+chickens. Now these monstrosities may be said to be directly caused by such
+unnatural conditions, but the modifications thus induced are not of a
+definite nature. An excellent observer, M. Camille Dareste,[712] remarks
+"that the various species of monstrosities are not determined by specific
+causes; the external agencies which modify the development of the embryo
+act solely in causing a perturbation--a perversion in the normal course of
+development." He compares the result to what we see in illness: a sudden
+chill, for instance, affects one individual alone out of many, causing
+either a cold, or sore-throat, rheumatism, or inflammation of the lungs or
+pleura. Contagious matter acts in an analogous manner.[713] We may take a
+still more specific instance: seven pigeons were struck by
+rattle-snakes;[714] some suffered from convulsions; some had their blood
+coagulated, in others it was perfectly fluid; some showed ecchymosed spots
+on the heart, others on the intestines, &c.; others again showed no visible
+lesion in any organ. It is well known that excess in drinking causes
+different diseases in different men; but men living under a cold and
+tropical climate are differently affected:[715] and in this case we see the
+definite influence of opposite conditions. The foregoing facts apparently
+give us as good an idea as we are likely for a long time to obtain, how in
+many cases external conditions act directly, though not definitely, in
+causing modifications of structure.
+
+       *       *       *       *       *
+
+_Summary._--There can be no doubt, from the facts given in the early part
+of this chapter, that extremely slight changes in {290} the conditions of
+life sometimes act in a definite manner on our already variable
+domesticated productions; and, as the action of changed conditions in
+causing general or indefinite variability is accumulative, so it may be
+with their definite action. Hence it is possible that great and definite
+modifications of structure may result from altered conditions acting during
+a long series of generations. In some few instances a marked effect has
+been produced quickly on all, or nearly all, the individuals which have
+been exposed to some considerable change of climate, food, or other
+circumstance. This has occurred, and is now occurring, with European men in
+the United States, with European dogs in India, with horses in the Falkland
+Islands, apparently with various animals at Angora, with foreign oysters in
+the Mediterranean, and with maize grown in Europe from tropical seed. We
+have seen that the chemical compounds secreted by plants and the state of
+their tissues are readily affected by changed conditions. In some cases a
+relation apparently exists between certain characters and certain
+conditions, so that if the latter be changed the character is lost--as with
+cultivated flowers, with some few culinary plants, with the fruit of the
+melon, with fat-tailed sheep, and other sheep having peculiar fleeces.
+
+The production of galls, and the change of plumage in parrots when fed on
+peculiar food or when inoculated by the poison of a toad, prove to us what
+great and mysterious changes in structure and colour may be the definite
+result of chemical changes in the nutrient fluids or tissues.
+
+We have also reason to believe that organic beings in a state of nature may
+be modified in various definite ways by the conditions to which they have
+been long exposed, as in the case of American trees in comparison with
+their representatives in Europe. But in all such cases it is most difficult
+to distinguish between the definite results of changed conditions, and the
+accumulation through natural selection of serviceable variations which have
+arisen independently of the nature of the conditions. If, for instance, a
+plant had to be modified so as to become fitted to inhabit a humid instead
+of an arid station, we have no reason to believe that variations of the
+right kind would occur more frequently if the parent-plant inhabited a
+station a little more {291} humid than usual. Whether the station was
+unusually dry or humid, variations adapting the plant in a slight degree
+for directly opposite habits of life would occasionally arise, as we have
+reason to believe from what we know in other cases.
+
+In most, perhaps in all cases, the organisation or constitution of the
+being which is acted on, is a much more important element than the nature
+of the changed conditions, in determining the nature of the variation. We
+have evidence of this in the appearance of nearly similar modifications
+under different conditions, and of different modifications under apparently
+nearly the same conditions. We have still better evidence of this in
+closely parallel varieties being frequently produced from distinct races,
+or even distinct species, and in the frequent recurrence of the same
+monstrosity in the same species. We have also seen that the degree to which
+domesticated birds have varied, does not stand in any close relation with
+the amount of change to which they have been subjected.
+
+To recur once again to bud-variations. When we reflect on the millions of
+buds which many trees have produced, before some one bud has varied, we are
+lost in wonder what the precise cause of each variation can be. Let us
+recall the case given by Andrew Knight of the forty-year-old tree of the
+yellow magnum bonum plum, an old variety which has been propagated by
+grafts on various stocks for a very long period throughout Europe and North
+America, and on which a single bud suddenly produced the red magnum bonum.
+We should also bear in mind that distinct varieties, and even distinct
+species,--as in the case of peaches, nectarines, and apricots,--of certain
+roses and camellias,--although separated by a vast number of generations
+from any progenitor in common, and although cultivated under diversified
+conditions, have yielded by bud-variation closely analogous varieties. When
+we reflect on these facts we become deeply impressed with the conviction
+that in such cases the nature of the variation depends but little on the
+conditions to which the plant has been exposed, and not in any especial
+manner on its individual character, but much more on the general nature or
+constitution, inherited from some remote progenitor, of the whole group of
+allied beings to which the plant belongs. We are thus driven to conclude
+that in most {292} cases the conditions of life play a subordinate part in
+causing any particular modification; like that which a spark plays, when a
+mass of combustibles bursts into flame--the nature of the flame depending
+on the combustible matter, and not on the spark.
+
+No doubt each slight variation must have its efficient cause; but it is as
+hopeless an attempt to discover the cause of each as to say why a chill or
+a poison affects one man differently from another. Even with modifications
+resulting from the definite action of the conditions of life, when all or
+nearly all the individuals, which have been similarly exposed, are
+similarly affected, we can rarely see the precise relation between cause
+and effect. In the next chapter it will be shown that the increased use or
+disuse of various organs, produces an inherited effect. It will further be
+seen that certain variations are bound together by correlation and other
+laws. Beyond this we cannot at present explain either the causes or manner
+of action of Variation.
+
+Finally, as indefinite and almost illimitable variability is the usual
+result of domestication and cultivation, with the same part or organ
+varying in different individuals in different or even in directly opposite
+ways; and as the same variation, if strongly pronounced, usually recurs
+only after long intervals of time, any particular variation would generally
+be lost by crossing, reversion, and the accidental destruction of the
+varying individuals, unless carefully preserved by man. Hence, although it
+must be admitted that new conditions of life do sometimes definitely affect
+organic beings, it may be doubted whether well-marked races have often been
+produced by the direct action of changed conditions without the aid of
+selection either by man or nature.
+
+       *       *       *       *       *
+
+
+{293}
+
+CHAPTER XXIV.
+
+LAWS OF VARIATION--USE AND DISUSE, ETC.
+
+    NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON
+    THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS
+    OF LIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY
+    WHICH THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS.
+
+In this and the two following chapters I shall discuss, as well as the
+difficulty of the subject permits, the several laws which govern
+Variability. These may be grouped under the effects of use and disuse,
+including changed habits and acclimatisation--arrests of
+development--correlated variation--the cohesion of homologous parts--the
+variability of multiple parts--compensation of growth--the position of buds
+with respect to the axis of the plant--and lastly, analogous variation.
+These several subjects so graduate into each other that their distinction
+is often arbitrary.
+
+It may be convenient first briefly to discuss that co-ordinating and
+reparative power which is common, in a higher or lower degree, to all
+organic beings, and which was formerly designated by physiologists as the
+_nisus formativus_.
+
+    Blumenbach and others[716] have insisted that the principle which
+    permits a Hydra, when cut into fragments, to develop itself into two or
+    more perfect animals, is the same with that which causes a wound in the
+    higher animals to heal by a cicatrice. Such cases as that of the Hydra
+    are evidently analogous with the spontaneous division or fissiparous
+    generation of the lowest animals, and likewise with the budding of
+    plants. Between these extreme cases and that of a mere cicatrice we
+    have every gradation. Spallanzani,[717] by cutting off the legs and
+    tail of a Salamander, got in the course of three months six crops of
+    these members; so that 687 perfect bones were reproduced by one animal
+    during one season. At whatever {294} point the limb was cut off, the
+    deficient part, and no more, was exactly reproduced. Even with man, as
+    we have seen in the twelfth chapter, when treating of polydactylism,
+    the entire limb whilst in an embryonic state, and supernumerary digits,
+    are occasionally, though imperfectly, reproduced after amputation. When
+    a diseased bone has been removed, a new one sometimes "gradually
+    assumes the regular form, and all the attachments of muscles,
+    ligaments, &c., become as complete as before."[718]
+
+    This power of regrowth does not, however, always act perfectly: the
+    reproduced tail of a lizard differs in the forms of the scales from the
+    normal tail: with certain Orthopterous insects the large hind legs are
+    reproduced of smaller size:[719] the white cicatrice which in the
+    higher animals unites the edges of a deep wound is not formed of
+    perfect skin, for elastic tissue is not produced till long
+    afterwards.[720] "The activity of the _nisus formativus_," says
+    Blumenbach, "is in an inverse ratio to the age of the organised body."
+    To this may be added that its power is greater in animals the lower
+    they are in the scale of organisation; and animals low in the scale
+    correspond with the embryos of higher animals belonging to the same
+    class. Newport's observations[721] afford a good illustration of this
+    fact, for he found that "myriapods, whose highest development scarcely
+    carries them beyond the larvae of perfect insects, can regenerate limbs
+    and antennae up to the time of their last moult;" and so can the larvae
+    of true insects, but not the mature insect. Salamanders correspond in
+    development with the tadpoles or larvae of the tailless Batrachians,
+    and both possess to a large extent the power of regrowth; but not so
+    the mature tailless Batrachians.
+
+    Absorption often plays an important part in the repairs of injuries.
+    When a bone is broken, and does not unite, the ends are absorbed and
+    rounded, so that a false joint is formed; or if the ends unite, but
+    overlap, the projecting parts are removed.[722] But absorption comes
+    into action, as Virchow remarks, during the normal growth of bones;
+    parts which are solid during youth become hollowed out for the
+    medullary tissue as the bone increases in size. In trying to understand
+    the many well-adapted cases of regrowth when aided by absorption, we
+    should remember that most parts of the organisation, even whilst
+    retaining the same form, undergo constant renewal; so that a part which
+    was not renewed would naturally be liable to complete absorption.
+
+    Some cases, usually classed under the so-called _nisus formativus_, at
+    first appear to come under a distinct head; for not only are old
+    structures reproduced, but structures which appear new are formed.
+    Thus, after inflammation "false membranes," furnished with
+    blood-vessels, lymphatics, and nerves, are developed; or a foetus
+    escapes from the Fallopian tubes, and falls into the abdomen, "nature
+    pours out a quantity of plastic lymph, which forms itself into
+    organised membrane, richly supplied with blood-vessels," and the foetus
+    is nourished for a time. In certain cases of {295} hydrocephalus the
+    open and dangerous spaces in the skull are filled up with new bones,
+    which interlock by perfect serrated sutures.[723] But most
+    physiologists, especially on the Continent, have now given up the
+    belief in plastic lymph or blastema, and Virchow[724] maintains that
+    every structure, new or old, is formed by the proliferation of
+    pre-existing cells. On this view false membranes, like cancerous or
+    other tumours, are merely abnormal developments of normal growths; and
+    we can thus understand how it is that they resemble adjoining
+    structures; for instance, that "false membrane in the serous cavities
+    acquires a covering of epithelium exactly like that which covers the
+    original serous membrane; adhesions of the iris may become black
+    apparently from the production of pigment-cells like those of the
+    uvea."[725]
+
+    No doubt the power of reparation, though not always quite perfect, is
+    an admirable provision, ready for various emergencies, even for those
+    which occur only at long intervals of time.[726] Yet this power is not
+    more wonderful than the growth and development of every single
+    creature, more especially of those which are propagated by fissiparous
+    generation. This subject has been here noticed, because we may infer
+    that, when any part or organ is either greatly increased in size or
+    wholly suppressed through variation and continued selection, the
+    co-ordinating power of the organisation will continually tend to bring
+    all the parts again into harmony with each other.
+
+_On the Effects of the Increased Use and Disuse of Organs._
+
+It is notorious, and we shall immediately adduce proofs, that increased use
+or action strengthens muscles, glands, sense-organs, &c.; and that disuse,
+on the other hand, weakens them. I have not met with any clear explanation
+of this fact in works on Physiology. Mr. Herbert Spencer[727] maintains
+that when muscles are much used, or when intermittent pressure is applied
+to the epidermis, an excess of nutritive matter exudes from the vessels,
+and that this gives additional development to the adjoining parts. That an
+increased flow of blood towards an organ leads to its greater development
+is probable, if not certain. Mr. Paget[728] thus accounts for the long,
+thick, and dark-coloured hair which occasionally grows, even in young
+children, near old-standing inflamed surfaces or fractured bones. When
+Hunter {296} inserted the spur of a cock into the comb, which is well
+supplied with blood-vessels, it grew in one case in a spiral direction to a
+length of six inches, and in another case forward, like a horn, so that the
+bird could not touch the ground with its beak. But whether Mr. Herbert
+Spencer's view of the exudation of nutritive matter due to increased
+movement and pressure, will fully account for the augmented size of bones,
+ligaments, and especially of internal glands and nerves, seems doubtful.
+According to the interesting observations of M. Sedillot,[729] when a
+portion of one bone of the leg or fore-arm of an animal is removed and is
+not replaced by growth, the associated bone enlarges till it attains a bulk
+equal to that of the two bones, of which it has to perform the functions.
+This is best exhibited in dogs in which the tibia has been removed; the
+companion bone, which is naturally almost filiform and not one-fifth the
+size of the other, soon acquires a size equal to or greater than the tibia.
+Now, it is at first difficult to believe that increased weight acting on a
+straight bone could, by alternately increased and diminished pressure,
+cause nutritive matter to exude from the vessels which permeate the
+periosteum. Nevertheless, the observations adduced by Mr. Spencer,[730] on
+the strengthening of the bowed bones of rickety children, along their
+concave sides, leads to the belief that this is possible.
+
+Mr. H. Spencer has also shown that the ascent of the sap in trees is aided
+by the rocking movement caused by the wind; and the sap strengthens the
+trunk "in proportion to the stress to be borne; since the more severe and
+the more repeated the strains, the greater must be the exudation from the
+vessels into the surrounding tissue, and the greater the thickening of this
+tissue by secondary deposits."[731] But woody trunks may be formed of hard
+tissue without their having been subjected to any movement, as we see with
+ivy closely attached to old walls. In all these cases, it is very difficult
+to disentangle the effects of long-continued selection from those
+consequent on the increased action or movement of the part. Mr. H.
+Spencer[732] acknowledges this difficulty, and gives as an instance the
+spines {297} or thorns of trees, and the shells of nuts. Here we have
+extremely hard woody tissue without the possibility of any movement to
+cause exudation, and without, as far as we can see, any other directly
+exciting cause; and as the hardness of these parts is of manifest service
+to the plant, we may look at the result as probably due to the selection of
+so-called spontaneous variations. Every one knows that hard work thickens
+the epidermis on the hands; and when we hear that with infants long before
+their birth the epidermis is thicker on the palms and soles of the feet
+than on any other part of the body, as was observed with admiration by
+Albinus,[733] we are naturally inclined to attribute this to the inherited
+effects of long-continued use or pressure. We are tempted to extend the
+same view even to the hoofs of quadrupeds; but who will pretend to
+determine how far natural selection may have aided in the formation of
+structures of such obvious importance to the animal?
+
+    That use strengthens the muscles may be seen in the limbs of artisans
+    who follow different trades; and when a muscle is strengthened, the
+    tendons, and the crests of bone to which they are attached, become
+    enlarged; and this must likewise be the case with the blood-vessels and
+    nerves. On the other hand, when a limb is not used, as by Eastern
+    fanatics, or when the nerve supplying it with nervous power is
+    effectually destroyed, the muscles wither. So again, when the eye is
+    destroyed the optic nerve becomes atrophied, sometimes even in the
+    course of a few months.[734] The Proteus is furnished with branchiae as
+    well as with lungs: and Schreibers[735] found that when the animal was
+    compelled to live in deep water the branchiae were developed to thrice
+    their ordinary size, and the lungs were partially atrophied. When, on
+    the other hand, the animal was compelled to live in shallow water, the
+    lungs became larger and more vascular, whilst the branchiae disappeared
+    in a more or less complete degree. Such modifications as these are,
+    however, of comparatively little value for us, as we do not actually
+    know that they tend to be inherited.
+
+    In many cases there is reason to believe that the lessened use of
+    various organs has affected the corresponding parts in the offspring.
+    But there is no good evidence that this ever follows in the course of a
+    single generation. It appears, as in the case of general or indefinite
+    variability, that several generations must be subjected to changed
+    habits for any appreciable result. Our domestic fowls, ducks, and geese
+    have almost lost, not {298} only in the individual but in the race,
+    their power of flight; for we do not see a chicken, when frightened,
+    take flight like a young pheasant. Hence I was led carefully to compare
+    the limb-bones of fowls, ducks, pigeons, and rabbits, with the same
+    bones in the wild parent-species. As the measurements and weights were
+    fully given in the earlier chapters, I need here only recapitulate the
+    results. With domestic pigeons, the length of the sternum, the
+    prominence of its crest, the length of the scapulae and furcula, the
+    length of the wings as measured from tip to tip of the radius, are all
+    reduced relatively to the same parts in the wild pigeon. The wing and
+    tail feathers, however, are increased in length, but this may have as
+    little connection with the use of the wings or tail, as the lengthened
+    hair on a dog with the amount of exercise which the breed has
+    habitually taken. The feet of pigeons, except in the long-beaked races,
+    are reduced in size. With fowls the crest of the sternum is less
+    prominent, and is often distorted or monstrous; the wing-bones have
+    become lighter relatively to the leg-bones, and are apparently a little
+    shorter in comparison with those of the parent-form, the _Gallus
+    bankiva_. With ducks, the crest of the sternum is affected in the same
+    manner as in the foregoing cases: the furcula, coracoids, and scapulae
+    are all reduced in weight relatively to the whole skeleton: the bones
+    of the wings are shorter and lighter, and the bones of the legs longer
+    and heavier, relatively to each other, and relatively to the whole
+    skeleton, in comparison with the same bones in the wild-duck. The
+    decreased weight and size of the bones, in the foregoing cases, is
+    probably the indirect result of the reaction of the weakened muscles on
+    the bones. I failed to compare the feathers of the wings of the tame
+    and wild duck; but Gloger[736] asserts that in the wild duck the tips
+    of the wing-feathers reach almost to the end of the tail, whilst in the
+    domestic duck they often hardly reach to its base. He remarks, also, on
+    the greater thickness of the legs, and says that the swimming membrane
+    between the toes is reduced; but I was not able to detect this latter
+    difference.
+
+    With the domesticated rabbit the body, together with the whole
+    skeleton, is generally larger and heavier than in the wild animal, and
+    the leg-bones are heavier in due proportion; but whatever standard of
+    comparison be taken, neither the leg-bones nor the scapulae have
+    increased in length proportionally with the increased dimensions of the
+    rest of the skeleton. The skull has become in a marked manner narrower,
+    and, from the measurements of its capacity formerly given, we may
+    conclude, that this narrowness results from the decreased size of the
+    brain, consequent on the mentally inactive life led by these
+    closely-confined animals.
+
+    We have seen in the eighth chapter that silk-moths, which have been
+    kept during many centuries closely confined, emerge from their cocoons
+    with their wings distorted, incapable of flight, often greatly reduced
+    in size, or even, according to Quatrefages, quite rudimentary. This
+    condition of the wings may be largely owing to the same kind of
+    monstrosity which often affects wild Lepidoptera when artificially
+    reared from the cocoon; or it may {299} be in part due to an inherent
+    tendency, which is common to the females of many Bombycidae, to have
+    their wings in a more or less rudimentary state; but part of the effect
+    may probably be attributed to long-continued disuse.
+
+From the foregoing facts there can be no doubt that certain parts of the
+skeleton in our anciently domesticated animals, have been modified in
+length and weight by the effects of decreased or increased use; but they
+have not been modified, as shown in the earlier chapters, in shape or
+structure. We must, however, be cautious in extending this latter
+conclusion to animals living a free life; for these will occasionally be
+exposed during successive generations to the severest competition. With
+wild animals it would be an advantage in the struggle for life that every
+superfluous and useless detail of structure should be removed or absorbed;
+and thus the reduced bones might ultimately become changed in structure.
+With highly-fed domesticated animals, on the other hand, there is no
+economy of growth; nor any tendency to the elimination of trifling and
+superfluous details of structure.
+
+Turning now to more general observations, Nathusius has shown that, with
+the improved races of the pig, the shortened legs and snout, the form of
+the articular condyles of the occiput, and the position of the jaws with
+the upper canine teeth projecting in a most anomalous manner in front of
+the lower canines, may be attributed to these parts not having been fully
+exercised. For the highly-cultivated races do not travel in search of food,
+nor root up the ground with their ringed muzzles. These modifications of
+structure, which are all strictly inherited, characterise several improved
+breeds, so that they cannot have been derived from any single domestic or
+wild stock.[737] With respect to cattle, Professor Tanner has remarked that
+the lungs and liver in the improved breeds "are found to be considerably
+reduced in size when compared with those possessed by animals having
+perfect liberty;"[738] and the reduction of these organs affects the
+general shape of the body. The cause of the reduced lungs in highly-bred
+animals which take little exercise is {300} obvious; and perhaps the liver
+may be affected by the nutritious and artificial food on which they largely
+subsist.
+
+    It is well known that, when an artery is tied, the anastomosing
+    branches, from being forced to transmit more blood, increase in
+    diameter; and this increase cannot be accounted for by mere extension,
+    as their coats gain in strength. Mr. Herbert Spencer[739] has argued
+    that with plants the flow of sap from the point of supply to the
+    growing part first elongates the cells in this line; and that the cells
+    then become confluent, thus forming the ducts; so that, on this view,
+    the vessels in plants are formed by the mutual reaction of the flowing
+    sap and cellular tissue. Dr. W. Turner has remarked,[740] with respect
+    to the branches of arteries, and likewise to a certain extent with
+    nerves, that the great principle of compensation frequently comes into
+    play; for "when two nerves pass to adjacent cutaneous areas, an inverse
+    relation as regards size may subsist between them; a deficiency in one
+    may be supplied by an increase in the other, and thus the area of the
+    former may be trespassed on by the latter nerve." But how far in these
+    cases the difference in size in the nerves and arteries is due to
+    original variation, and how far to increased use or action, is not
+    clear.
+
+    In reference to glands, Mr. Paget observes that "when one kidney is
+    destroyed the other often becomes much larger, and does double
+    work."[741] If we compare the size of the udders and their power of
+    secretion in cows which have been long domesticated, and in certain
+    goats in which the udders nearly touch the ground, with the size and
+    power of secretion of these organs in wild or half-domesticated
+    animals, the difference is great. A good cow with us daily yields more
+    than five gallons, or forty pints of milk, whilst a first-rate animal,
+    kept, for instance, by the Damaras of South Africa,[742] "rarely gives
+    more than two or three pints of milk daily, and, should her calf be
+    taken from her, she absolutely refuses to give any." We may attribute
+    the excellence of our cows, and of certain goats, partly to the
+    continued selection of the best milking animals, and partly to the
+    inherited effects of the increased action, through man's art, of the
+    secreting glands.
+
+    It is notorious, as was remarked in the twelfth chapter, that
+    short-sight is inherited; and if we compare watchmakers or engravers
+    with, for instance, sailors, we can hardly doubt that vision
+    continually directed towards a near object permanently affects the
+    structure of the eye.
+
+    Veterinarians are unanimous that horses become affected with spavins,
+    splints, ringbones, &c., from being shod, and from travelling on hard
+    roads, and they are almost equally unanimous that these injuries are
+    transmitted. Formerly horses were not shod in North Carolina, and it
+    has been asserted that they did not then suffer from these diseases of
+    the legs and feet.[743]
+
+{301}
+
+Our domesticated quadrupeds are all descended, as far as is known, from
+species having erect ears; yet few kinds can be named, of which at least
+one race has not drooping ears. Cats in China, horses in parts of Russia,
+sheep in Italy and elsewhere, the guinea-pig in Germany, goats and cattle
+in India, rabbits, pigs, and dogs in all long-civilised countries, have
+dependent ears. With wild animals, which constantly use their ears like
+funnels to catch every passing sound, and especially to ascertain the
+direction whence it comes, there is not, as Mr. Blyth has remarked, any
+species with drooping ears except the elephant. Hence the incapacity to
+erect the ears is certainly in some manner the result of domestication; and
+this incapacity has been attributed by various authors[744] to disuse, for
+animals protected by man are not compelled habitually to use their ears.
+Col. Hamilton Smith[745] states that in ancient effigies of the dog, "with
+the exception of one Egyptian instance, no sculpture of the earlier Grecian
+era produces representations of hounds with completely drooping ears; those
+with them half pendulous are missing in the most ancient; and this
+character increases, by degrees, in the works of the Roman period." Godron
+also has remarked that "the pigs of the ancient Egyptians had not their
+ears enlarged and pendent."[746] But it is remarkable that the drooping of
+the ears, though probably the effect of disuse, is not accompanied by any
+decrease in size; on the contrary, when we remember that animals so
+different as fancy rabbits, certain Indian breeds of the goat, our petted
+spaniels, bloodhounds, and other dogs, have enormously elongated ears, it
+would appear as if disuse actually caused an increase in length. With
+rabbits, the drooping of the much elongated ears has affected even the
+structure of the skull.
+
+The tail of no wild animal, as remarked to me by Mr. Blyth, is curled;
+whereas pigs and some races of dogs have their tails much curled. This
+deformity, therefore, appears to be the result of domestication, but
+whether in any way connected with the lessened use of the tail is doubtful.
+
+{302}
+
+The epidermis on our hands is easily thickened, as every one knows, by hard
+work. In a district of Ceylon the sheep have "horny callosities that defend
+their knees, and which arise from their habit of kneeling down to crop the
+short herbage, and this distinguishes the Jaffna flocks from those of other
+portions of the island;" but it is not stated whether this peculiarity is
+inherited.[747]
+
+The mucous membrane which lines the stomach is continuous with the external
+skin of the body; therefore it is not surprising that its texture should be
+affected by the nature of the food consumed, but other and more interesting
+changes likewise follow. Hunter long ago observed that the muscular coat of
+the stomach of a gull (_Larus tridactylus_) which had been fed for a year
+chiefly on grain was thickened; and, according to Dr. Edmondston, a similar
+change periodically occurs in the Shetland Islands in the stomach of the
+_Larus argentatus_, which in the spring frequents the corn-fields and feeds
+on the seed. The same careful observer has noticed a great change in the
+stomach of a raven which had been long fed on vegetable food. In the case
+of an owl (_Strix grallaria_) similarly treated, Menetries states that the
+form of the stomach was changed, the inner coat became leathery, and the
+liver increased in size. Whether these modifications in the digestive
+organs would in the course of generations become inherited is not
+known.[748]
+
+The increased or diminished length of the intestines, which apparently
+results from changed diet, is a more remarkable case, because it is
+characteristic of certain animals in their domesticated condition, and
+therefore must be inherited. The complex absorbent system, the
+blood-vessels, nerves, and muscles, are necessarily all modified together
+with the intestines. According to Daubenton, the intestines of the domestic
+cat are one-third longer than those of the wild cat of Europe; and although
+this species is not the parent-stock of the domestic animal, yet, as
+Isidore Geoffroy has remarked, the several species {303} of cats are so
+closely allied that the comparison is probably a fair one. The increased
+length appears to be due to the domestic cat being less strictly
+carnivorous in its diet than any wild feline species; I have seen a French
+kitten eating vegetables as readily as meat. According to Cuvier, the
+intestines of the domesticated pig exceed greatly in proportionate length
+those of the wild boar. In the tame and wild rabbit the change is of an
+opposite nature, and probably results from the nutritious food given to the
+tame rabbit.[749]
+
+       *       *       *       *       *
+
+_Changed Habits of Life, independently of the Use or Disuse of particular
+Organs._--This subject, as far as the mental powers of animals are
+concerned, so blends into instinct, on which I shall treat in a future
+work, that I will here only remind the reader of the many cases which occur
+under domestication, and which are familiar to every one--for instance the
+tameness of our animals--the pointing or retrieving of dogs--their not
+attacking the smaller animals kept by man--and so forth. How much of these
+changes ought to be attributed to inherited habit, and how much to the
+selection of individuals which have varied in the desired manner,
+irrespectively of the special circumstances under which they have been
+kept, can seldom be told. We have already seen that animals may be
+habituated to a changed diet; but a few additional instances may here be
+given.
+
+In the Polynesian Islands and in China the dog is fed exclusively on
+vegetable matter, and the taste for this kind of food is to a certain
+extent inherited.[750] Our sporting dogs will not touch the bones of game
+birds, whilst other dogs devour them with greediness. In some parts of the
+world sheep have been largely fed on fish. The domestic hog is fond of
+barley, the wild boar is said to disdain it; and the disdain is partially
+inherited, for some young wild pigs bred in captivity showed an aversion
+for this grain, whilst others of the same brood relished it.[751] One of my
+relations bred some young pigs from {304} a Chinese sow by a wild Alpine
+boar; they lived free in the park, and were so tame that they came to the
+house to be fed; but they would not touch swill, which was devoured by the
+other pigs. An animal when once accustomed to an unnatural diet, which can
+generally be effected only during youth, dislikes its proper food, as
+Spallanzani found to be the case with a pigeon which had been long fed on
+meat. Individuals of the same species take to new food with different
+degrees of readiness; one horse, it is stated, soon learned to eat meat,
+whilst another would have perished from hunger rather than have partaken of
+it.[752]
+
+The caterpillars of the _Bombyx hesperus_ feed in a state of nature on the
+leaves of the _Cafe diable_, but, after having been reared on the
+Ailanthus, they would not touch the _Cafe diable_, and actually died of
+hunger.[753]
+
+It has been found possible to accustom marine fish to live in fresh water;
+but as such changes in fish, and other marine animals, have been chiefly
+observed in a state of nature, they do not properly belong to our present
+subject. The period of gestation and of maturity, as shown in the earlier
+chapters,--the season and the frequency of the act of breeding,--have all
+been greatly modified under domestication. With the Egyptian goose the rate
+of change in the season has been recorded.[754] The wild drake pairs with
+one female, the domestic drake is polygamous. Certain breeds of fowls have
+lost the habit of incubation. The paces of the horse, and the manner of
+flight in certain breeds of the pigeon, have been modified, and are
+inherited. The voice differs much in certain fowls and pigeons. Some breeds
+are clamorous and others silent, as in the Call and common duck, or in the
+Spitz and pointer dog. Every one knows how dogs differ from each other in
+their manner of hunting, and in their ardour after different kinds of game
+or vermin.
+
+With plants the period of vegetation is easily changed and is inherited, as
+in the case of summer and winter wheat, barley, {305} and vetches; but to
+this subject we shall immediately return under acclimatisation. Annual
+plants sometimes become perennial under a new climate, as I hear from Dr.
+Hooker is the case with the stock and mignonette in Tasmania. On the other
+hand, perennials sometimes become annuals, as with the Ricinus in England,
+and as, according to Captain Mangles, with many varieties of the
+heartsease. Von Berg[755] raised from seed of _Verbascum phoenicium_, which
+is usually a biennial, both annual and perennial varieties. Some deciduous
+bushes become evergreen in hot countries.[756] Rice requires much water,
+but there is one variety in India which can be grown without
+irrigation.[757] Certain varieties of the oat and of our other cereals are
+best fitted for certain soils.[758] Endless similar facts could be given in
+the animal and vegetable kingdoms. They are noticed here because they
+illustrate analogous differences in closely allied natural species, and
+because such changed habits of life, whether due to use and disuse, or to
+the direct action of external conditions, or to so-called spontaneous
+variation, would be apt to lead to modifications of structure.
+
+       *       *       *       *       *
+
+_Acclimatisation._--From the previous remarks we are naturally led to the
+much disputed subject of acclimatisation. There are two distinct questions:
+Do varieties descended from the same species differ in their power of
+living under different climates? And secondly, if they so differ, how have
+they become thus adapted? We have seen that European dogs do not succeed
+well in India, and it is asserted,[759] that no one has succeeded in there
+keeping the Newfoundland long alive; but then it may be argued, probably
+with truth, that these northern breeds are specifically distinct from the
+native dogs which flourish in India. The same remark may be made with
+respect to different breeds of sheep, of which, according to Youatt,[760]
+not one brought "from a torrid climate lasts out the second year," in the
+Zoological Gardens. But sheep are capable of some degree of
+acclimatisation, for Merino sheep bred at the Cape of Good Hope have been
+found {306} far better adapted for India than those imported from
+England.[761] It is almost certain that the breeds of the fowl are
+descended from the same species; but the Spanish breed, which there is good
+reason to believe originated near the Mediterranean,[762] though so fine
+and vigorous in England, suffers more from frost than any other breed. The
+Arrindy silk-moth introduced from Bengal, and the Ailanthus moth from the
+temperate province of Shan Tung, in China, belong to the same species, as
+we may infer from their identity in the caterpillar, cocoon, and mature
+states;[763] yet they differ much in constitution: the Indian form "will
+flourish only in warm latitudes," the other is quite hardy and withstands
+cold and rain.
+
+    Plants are more strictly adapted to climate than are animals. The
+    latter when domesticated withstand such great diversities of climate,
+    that we find nearly the same species in tropical and temperate
+    countries; whilst the cultivated plants are widely dissimilar. Hence a
+    larger field is open for inquiry in regard to the acclimatisation of
+    plants than of animals. It is no exaggeration to say that with almost
+    every plant which has long been cultivated varieties exist, which are
+    endowed with constitutions fitted for very different climates; I will
+    select only a few of the more striking cases, as it would be tedious to
+    give all. In North America numerous fruit-trees have been raised, and
+    in horticultural publications,--for instance, in Downing,--lists are
+    given of the varieties which are best able to withstand the severe
+    climate of the northern States and Canada. Many American varieties of
+    the pear, plum, and peach are excellent in their own country, but until
+    recently hardly one was known that succeeded in England; and with
+    apples,[764] not one succeeds. Though the American varieties can
+    withstand a severer winter than ours, the summer here is not hot
+    enough. Fruit-trees have originated in Europe as in America with
+    different constitutions, but they are not here much noticed, as the
+    same nurserymen do not supply a wide area. The Forelle pear flowers
+    early, and when the flowers have just set, and this is the critical
+    period, they have been observed, both in France and England, to
+    withstand with complete impunity a frost of 18deg and even 14deg Fahr.,
+    which killed the flowers, whether fully expanded or in bud, of all
+    other kinds of pears.[765] This power in the flower of resisting cold
+    and afterwards producing fruit does not invariably depend, as we know
+    on good authority,[766] on general constitutional vigour.
+
+    {307}
+
+    In proceeding northward, the number of varieties which are enabled to
+    resist the climate rapidly decreases, as may be seen in the list of the
+    varieties of the cherry, apple, and pear, which can be cultivated in
+    the neighbourhood of Stockholm.[767] Near Moscow, Prince Troubetzkoy
+    planted for experiment in the open ground several varieties of the
+    pear, but one alone, the _Poire sans Pepins_, withstood the cold of
+    winter.[768] We thus see that our fruit-trees, like distinct species of
+    the same genus, certainly differ from each other in their
+    constitutional adaptation to different climates.
+
+    With the varieties of many plants, the adaptation to climate is often
+    very close. Thus it has been proved by repeated trials "that few if any
+    of the English varieties of wheat are adapted for cultivation in
+    Scotland;"[769] but the failure in this case is at first only in the
+    quantity, though ultimately in the quality, of the grain produced. The
+    Rev. J. M. Berkeley sowed wheat-seed from India, and got "the most
+    meagre ears," on land which would certainly have yielded a good crop
+    from English wheat.[770] In these cases varieties have been carried
+    from a warmer to a cooler climate; in the reverse case, as "when wheat
+    was imported directly from France into the West Indian Islands, it
+    produced either wholly barren spikes or furnished with only two or
+    three miserable seeds, while West Indian seed by its side yielded an
+    enormous harvest."[771] Here is another case of close adaptation to a
+    slightly cooler climate; a kind of wheat which in England may be used
+    indifferently either as a winter or summer variety, when sown under the
+    warmer climate of Grignan, in France, behaved exactly as if it had been
+    a true winter wheat.[772]
+
+    Botanists believe that all the varieties of maize belong to the same
+    species; and we have seen that in North America, in proceeding
+    northward, the varieties cultivated in each zone produce their flowers
+    and ripen their seed within shorter and shorter periods. So that the
+    tall, slowly maturing southern varieties do not succeed in New England,
+    and the New English varieties do not succeed in Canada. I have not met
+    with any statement that the southern varieties are actually injured or
+    killed by a degree of cold which the northern varieties withstand with
+    impunity, though this is probable; but the production of early
+    flowering and early seeding varieties deserves to be considered as one
+    form of acclimatisation. Hence it has been found possible, according to
+    Kalm, to cultivate maize further and further northwards in America. In
+    Europe, also, as we learn from the evidence given by Alph. De Candolle,
+    the culture of maize has extended since the end of the last century
+    thirty leagues north of its former boundary.[773] On the authority of
+    the great Linnaeus,[774] I may quote an {308} analogous case, namely,
+    that in Sweden tobacco raised from home-grown seed ripens its seed a
+    month sooner and is less liable to miscarry than plants raised from
+    foreign seed.
+
+    With the Vine, differently from the maize, the line of practical
+    culture has retreated a little southward since the middle ages;[775]
+    but this seems due to commerce, including that of wine, being now freer
+    or more easy. Nevertheless the fact of the vine not having spread
+    northward shows that acclimatisation has made no progress during
+    several centuries. There is, however, a marked difference in the
+    constitution of the several varieties,--some being hardy, whilst
+    others, like the muscat of Alexandria, require a very high temperature
+    to come to perfection. According to Labat,[776] vines taken from France
+    to the West Indies succeed with extreme difficulty, whilst those
+    imported from Madeira, or the Canary Islands, thrive admirably.
+
+    Gallesio gives a curious account of the naturalisation of the Orange in
+    Italy. Daring many centuries the sweet orange was propagated
+    exclusively by grafts, and so often suffered from frosts that it
+    required protection. After the severe frost of 1709, and more
+    especially after that of 1763, so many trees were destroyed that
+    seedlings from the sweet orange were raised, and, to the surprise of
+    the inhabitants, their fruit was found to be sweet. The trees thus
+    raised were larger, more productive, and hardier than the former kinds;
+    and seedlings are now continually raised. Hence Gallesio concludes that
+    much more was effected for the naturalisation of the orange in Italy by
+    the accidental production of new kinds during a period of about sixty
+    years, than had been effected by grafting old varieties during many
+    ages.[777] I may add that Risso[778] describes some Portuguese
+    varieties of the orange as extremely sensitive to cold, and as much
+    tenderer than certain other varieties.
+
+    The peach was known to Theophrastus, 322 B.C.[779] According to the
+    authorities quoted by Dr. F. Rolle,[780] it was tender when first
+    introduced into Greece, and even in the island of Rhodes only
+    occasionally bore fruit. If this be correct, the peach, in spreading
+    during the last two thousand years over the middle parts of Europe,
+    must have become much hardier. At the present day different varieties
+    differ much in hardiness: some French varieties will not succeed in
+    England; and near Paris, the _Pavie de Bonneuil_ does not ripen its
+    fruit till very late, even when grown on a wall; "it is, therefore,
+    only fit for a very hot southern climate."[781]
+
+    I will briefly give a few other cases. A variety of _Magnolia
+    grandiflora_, raised by M. Roy, withstands cold several degrees lower
+    than that which any other variety can resist. With camellias there is
+    much difference in hardiness. One particular variety of Noisette rose
+    withstood the severe frost of 1860 "untouched and hale amidst a
+    universal destruction of other {309} Noisettes." In New York the "Irish
+    yew is quite hardy, but the common yew is liable to be cut down." I may
+    add that there are varieties of the sweet potato (_Convolvulus
+    batatas_) which are suited for warmer, as well as for colder,
+    climates.[782]
+
+The plants as yet mentioned have been found capable of resisting an unusual
+degree of cold or heat, when fully grown. The following cases refer to
+plants whilst young. In a large bed of young Araucarias of the same age,
+growing close together and equally exposed, it was observed,[783] after the
+unusually severe winter of 1860-61, that, "in the midst of the dying,
+numerous individuals remained on which the frost had absolutely made no
+kind of impression." Dr. Lindley, after alluding to this and other similar
+cases, remarks, "Among the lessons which the late formidable winter has
+taught us, is that, even in their power of resisting cold, individuals of
+the same species of plants are remarkably different." Near Salisbury, there
+was a sharp frost on the night of May 24th, 1836, and all the French beans
+(_Phaseolus vulgaris_) in a bed were killed except about one in thirty,
+which completely escaped.[784] On the same day of the month, but in the
+year 1864, there was a severe frost in Kent, and two rows of
+scarlet-runners (_P. multiflorus_) in my garden, containing 390 plants of
+the same age and equally exposed, were all blackened and killed except
+about a dozen plants. In an adjoining row of "Fulmer's dwarf bean" (_P.
+vulgaris_), one single plant escaped. A still more severe frost occurred
+four days afterwards, and of the dozen plants which had previously escaped
+only three survived; these were not taller or more vigorous than the other
+young plants, but they escaped completely, with not even the tips of their
+leaves browned. It was impossible to behold these three plants, with their
+blackened, withered, and dead brethren all round them, and not see at a
+glance that they differed widely in constitutional power of resisting
+frost.
+
+This work is not the proper place to show that wild plants {310} of the
+same species, naturally growing at different altitudes or under different
+latitudes, become to a certain extent acclimatised, as is proved by the
+different behaviour of their seedlings when raised in England. In my
+'Origin of Species' I have alluded to some cases, and I could add others.
+One instance must suffice: Mr. Grigor, of Forres,[785] states that
+seedlings of the Scotch fir (_Pinus sylvestris_), raised from seed from the
+Continent and from the forests of Scotland, differ much. "The difference is
+perceptible in one-year-old, and more so in two-year-old seedlings; but the
+effects of the winter on the second year's growth almost uniformly makes
+those from the Continent quite brown, and so damaged, that by the month of
+March they are quite unsaleable, while the plants from the native Scotch
+pine, under the same treatment, and standing alongside, although
+considerably shorter, are rather stouter and quite green, so that the beds
+of the one can be known from the other when seen from the distance of a
+mile." Closely similar facts have been observed with seedling larches.
+
+    Hardy varieties would alone be valued or noticed in Europe; whilst
+    tender varieties, requiring more warmth, would generally be neglected;
+    but such occasionally arise. Thus Loudon[786] describes a Cornish
+    variety of the elm which is almost an evergreen, and of which the
+    shoots are often killed by the autumnal frosts, so that its timber is
+    of little value. Horticulturists know that some varieties are much more
+    tender than others: thus all the varieties of the broccoli are more
+    tender than cabbages; but there is much difference in this respect in
+    the sub-varieties of the broccoli; the pink and purple kinds are a
+    little hardier than the white Cape broccoli, "but they are not to be
+    depended on after the thermometer falls below 24deg Fahr.:" the
+    Walcheren broccoli is less tender than the Cape, and there are several
+    varieties which will stand much severer cold than the Walcheren.[787]
+    Cauliflowers seed more freely in India than cabbages.[788] To give one
+    instance with flowers: eleven plants raised from a hollyhock, called
+    the _Queen of the Whites_,[789] were found to be much more tender than
+    various other seedlings. It may be presumed that all tender varieties
+    would succeed better under a climate warmer than ours. With
+    fruit-trees, it is well known that certain varieties, for instance of
+    the peach, stand forcing in a hot-house better than others; and this
+    shows {311} either pliability of organisation or some constitutional
+    difference. The same individual cherry-tree, when forced, has been
+    observed during successive years gradually to change its period of
+    vegetation.[790] Few pelargoniums can resist the heat of a stove, but
+    _Alba multiflora_ will, as a most skilful gardener asserts, "stand
+    pine-apple top and bottom heat the whole winter, without looking any
+    more drawn than if it had stood in a common greenhouse; and _Blanche
+    Fleur_ seems as if it had been made on purpose for growing in winter,
+    like many bulbs, and to rest all summer."[791] There can hardly be a
+    doubt that the _Alba multiflora_ pelargonium must have a widely
+    different constitution from that of most other varieties of this plant;
+    it would probably withstand even an equatorial climate.
+
+    We have seen that according to Labat the vine and wheat require
+    acclimatisation in order to succeed in the West Indies. Similar facts
+    have been observed at Madras: "two parcels of mignonette-seed, one
+    direct from Europe, the other saved at Bangalore (of which the mean
+    temperature is much below that of Madras) were sown at the same time:
+    they both vegetated equally favourably, but the former all died off a
+    few days after they appeared above ground; the latter still survive,
+    and are vigorous healthy plants." So again, "turnip and carrot seed
+    saved at Hyderabad are found to answer better at Madras than seed from
+    Europe or from the Cape of Good Hope."[792] Mr. J. Scott, of the
+    Calcutta Botanic Gardens, informs me that seeds of the sweet-pea
+    (_Lathyrus odoratus_) imported from England produce plants, with thick,
+    rigid stems and small leaves, which rarely blossom and never yield
+    seed; plants raised from French seed blossom sparingly, but all the
+    flowers are sterile; on the other hand, plants raised from sweet-peas
+    grown near Darjeeling in Upper India, but originally derived from
+    England, can be successfully cultivated on the plains of India; for
+    they flower and seed profusely, and their stems are lax and scandent.
+    In some of the foregoing cases, as Dr. Hooker has remarked to me, the
+    greater success may perhaps be attributed to the seeds having been more
+    fully ripened under a more favourable climate; but this view can hardly
+    be extended to so many cases, including plants, which, from being
+    cultivated under a climate hotter than their native one, become fitted
+    for a still hotter climate. We may therefore safely conclude that
+    plants can to a certain extent become accustomed to a climate either
+    hotter or colder than their own; although these latter cases have been
+    more frequently observed.
+
+We will now consider the means by which acclimatisation may be effected,
+namely, through the spontaneous appearance of varieties having a different
+constitution, and through the effects of use or habit. In regard to the
+first process, there is no evidence that a change in the constitution of
+the {312} offspring necessarily stands in any direct relation with the
+nature of the climate inhabited by the parents. On the contrary, it is
+certain that hardy and tender varieties of the same species appear in the
+same country. New varieties thus spontaneously arising become fitted to
+slightly different climates in two different ways; firstly, they may have
+the power, either as seedlings or when full-grown, of resisting intense
+cold, as with the Moscow pear, or of resisting intense heat, as with some
+kinds of Pelargonium, or the flowers may withstand severe frost, as with
+the Forelle pear. Secondly, plants may become adapted to climates widely
+different from their own, from flowering and fruiting either earlier or
+later in the season. In both these cases the power of acclimatisation by
+man consists simply in the selection and preservation of new varieties. But
+without any direct intention on his part of securing a hardier variety,
+acclimatisation may be unconsciously effected by merely raising tender
+plants from seed, and by occasionally attempting their cultivation further
+and further northwards, as in the case of maize, the orange, and the peach.
+
+How much influence ought to be attributed to inherited habit or custom in
+the acclimatisation of animals and plants is a much more difficult
+question. In many cases natural selection can hardly have failed to have
+come into play and complicated the result. It is notorious that mountain
+sheep resist severe weather and storms of snow which would destroy lowland
+breeds; but then mountain sheep have been thus exposed from time
+immemorial, and all delicate individuals will have been destroyed, and the
+hardiest preserved. So with the Arrindy silk-moths of China and India; who
+can tell how far natural selection may have taken a share in the formation
+of the two races, which are now fitted for such widely different climates?
+It seems at first probable that the many fruit-trees, which are so well
+fitted for the hot summers and cold winters of North America, in contrast
+with their poor success under our climate, have become adapted through
+habit; but when we reflect on the multitude of seedlings annually raised in
+that country, and that none would succeed unless born with a fitting
+constitution, it is possible that mere habit may have done nothing towards
+their acclimatisation. On the other hand, when we {313} hear that Merino
+sheep, bred during no great number of generations at the Cape of Good
+Hope--that some European plants raised during only a few generations in the
+cooler parts of India, withstand the hotter parts of that country much
+better than the sheep or seeds imported directly from England, we must
+attribute some influence to habit. We are led to the same conclusion when
+we hear from Naudin[793] that the races of melons, squashes, and gourds,
+which have long been cultivated in Northern Europe, are comparatively more
+precocious, and need much less heat for maturing their fruit, than the
+varieties of the same species recently brought from tropical regions. In
+the reciprocal conversion of summer and winter wheat, barley, and vetches
+into each other, habit produces a marked effect in the course of a very few
+generations. The same thing apparently occurs with the varieties of maize,
+which, when carried from the Southern to the Northern States of America, or
+into Germany, soon become accustomed to their new homes. With vine-plants
+taken to the West Indies from Madeira, which are said to succeed better
+than plants brought directly from France, we have some degree of
+acclimatisation in the individual, independently of the production of new
+varieties by seed.
+
+The common experience of agriculturists is of some value, and they often
+advise persons to be cautious in trying in one country the productions of
+another. The ancient agricultural writers of China recommend the
+preservation and cultivation of the varieties peculiar to each country.
+During the classical period, Columella wrote, "Vernaculum pecus peregrino
+longe praestantius est."[794]
+
+I am aware that the attempt to acclimatise either animals or plants has
+been called a vain chimaera. No doubt the attempt in most cases deserves to
+be thus called, if made independently of the production of new varieties
+endowed with a different constitution. Habit, however much prolonged,
+rarely produces any effect on a plant propagated by buds; it apparently
+acts only through successive seminal generations. {314} The laurel, bay,
+laurestinus, &c., and the Jerusalem artichoke, which are propagated by
+cuttings or tubers, are probably now as tender in England as when first
+introduced; and this appears to be the case with the potato, which until
+recently was seldom multiplied by seed. With plants propagated by seed, and
+with animals, there will be little or no acclimatisation unless the hardier
+individuals are either intentionally or unconsciously preserved. The
+kidney-bean has often been advanced as an instance of a plant which has not
+become hardier since its first introduction into Britain. We hear, however,
+on excellent authority,[795] that some very fine seed, imported from
+abroad, produced plants "which blossomed most profusely, but were nearly
+all but abortive, whilst plants grown alongside from English seed podded
+abundantly;" and this apparently shows some degree of acclimatisation in
+our English plants. We have also seen that seedlings of the kidney-bean
+occasionally appear with a marked power of resisting frost; but no one, as
+far as I can hear, has ever separated such hardy seedlings, so as to
+prevent accidental crossing, and then gathered their seed, and repeated the
+process year after year. It may, however, be objected with truth that
+natural selection ought to have had a decided effect on the hardiness of
+our kidney-beans; for the tenderest individuals must have been killed
+during every severe spring, and the hardier preserved. But it should be
+borne in mind that the result of increased hardiness would simply be that
+gardeners, who are always anxious for as early a crop as possible, would
+sow their seed a few days earlier than formerly. Now, as the period of
+sowing depends much on the soil and elevation of each district, and varies
+with the season; and as new varieties have often been imported from abroad,
+can we feel sure that our kidney-beans are not somewhat hardier? I have not
+been able, by searching old horticultural works, to answer this question
+satisfactorily.
+
+On the whole the facts now given show that, though habit does something
+towards acclimatisation, yet that the spontaneous appearance of
+constitutionally different individuals is a far more effective agent. As no
+single instance has been recorded, either with animals or plants, of
+hardier individuals {315} having been long and steadily selected, though
+such selection is admitted to be indispensable for the improvement of any
+other character, it is not surprising that man has done little in the
+acclimatisation of domesticated animals and cultivated plants. We need not,
+however, doubt that under nature new races and new species would become
+adapted to widely different climates, by spontaneous variation, aided by
+habit, and regulated by natural selection.
+
+_Arrests of Development: Rudimentary and Aborted Organs._
+
+    These subjects are here introduced because there is reason to believe
+    that rudimentary organs are in many cases the result of disuse.
+    Modifications of structure from arrested development, so great or so
+    serious as to deserve to be called monstrosities, are of common
+    occurrence, but, as they differ much from any normal structure, they
+    require here only a passing notice. When a part or organ is arrested
+    during its embryonic growth, a rudiment is generally left. Thus the
+    whole head may be represented by a soft nipple-like projection, and the
+    limbs by mere papillae. These rudiments of limbs are sometimes
+    inherited, as has been observed in a dog.[796]
+
+    Many lesser anomalies in our domesticated animals appear to be due to
+    arrested development. What the cause of the arrest may be, we seldom
+    know, except in the case of direct injury to the embryo within the egg
+    or womb. That the cause does not generally act at a very early
+    embryonic period we may infer from the affected organ seldom being
+    wholly aborted,--a rudiment being generally preserved. The external
+    ears are represented by mere vestiges in a Chinese breed of sheep; and
+    in another breed, the tail is reduced "to a little button, suffocated,
+    in a manner, by fat."[797] In tailless dogs and cats a stump is left;
+    but I do not know whether it includes at an early embryonic age
+    rudiments of all the caudal vertebrae. In certain breeds of fowls the
+    comb and wattles are reduced to rudiments; in the Cochin-China breed
+    scarcely more than rudiments of spurs exist. With polled Suffolk
+    cattle, "rudiments of horns can often be felt at an early age;"[798]
+    and with species in a state of nature, the relatively greater
+    development of rudimentary organs at an early period of life is highly
+    characteristic of such organs. With hornless breeds of cattle and
+    sheep; another and singular kind of rudiment has been observed, namely,
+    minute dangling horns attached to the skin alone, and which are often
+    shed and grow again. With hornless goats, according to Desmarest,[799]
+    {316} the bony protuberances which properly support the horns exist as
+    mere rudiments.
+
+    With cultivated plants it is far from rare to find the petals, stamens,
+    and pistils represented by rudiments, like those observed in natural
+    species. So it is with the whole seed in many fruits; thus near
+    Astrakhan there is a grape with mere traces of seeds, "so small and
+    lying so near the stalk that they are not perceived in eating the
+    grape."[800] In certain varieties of the gourd, the tendrils, according
+    to Naudin, are represented by rudiments or by various monstrous
+    growths. In the broccoli and cauliflower the greater number of the
+    flowers are incapable of expansion, and include rudimentary organs. In
+    the Feather hyacinth (_Muscari comosum_) the upper and central flowers
+    are brightly coloured but rudimentary; under cultivation the tendency
+    to abortion travels downwards and outwards, and all the flowers become
+    rudimentary; but the abortive stamens and pistils are not so small in
+    the lower as in the upper flowers. In the _Viburnum opulus_, on the
+    other hand, the outer flowers naturally have their organs of
+    fructification in a rudimentary state, and the corolla is of large
+    size; under cultivation, the change spreads to the centre, and all the
+    flowers become affected; thus the well-known Snow-ball bush is
+    produced. In the Compositae, the so-called doubling of the flowers
+    consists in the greater development of the corolla of the central
+    florets, generally accompanied with some degree of sterility; and it
+    has been observed[801] that the progressive doubling invariably spreads
+    from the circumference to the centre,--that is, from the ray florets,
+    which so often include rudimentary organs, to those of the disc. I may
+    add, as bearing on this subject, that, with Asters, seeds taken from
+    the florets of the circumference have been found to yield the greatest
+    number of double flowers.[802] In these several cases we have a natural
+    tendency in certain parts to become rudimentary, and this under culture
+    spreads either to, or from, the axis of the plant. It deserves notice,
+    as showing how the same laws govern the changes which natural species
+    and artificial varieties undergo, that in a series of species in the
+    genus Carthamus, one of the Compositae, a tendency in the seeds to the
+    abortion of the pappus may be traced extending from the circumference
+    to the centre of the disc: thus, according to A. de Jussieu,[803] the
+    abortion is only partial in _Carthamus creticus_, but more extended in
+    _C. lanatus_; for in this species two or three alone of the central
+    seeds are furnished with a pappus, the surrounding seeds being either
+    quite naked or furnished with a few hairs; and lastly, in _C.
+    tinctorius_, even the central seeds are destitute of pappus, and the
+    abortion is complete.
+
+    With animals and plants under domestication, when an organ disappears,
+    leaving only a rudiment, the loss has generally been sudden, as with
+    hornless and tailless breeds; and such cases may be ranked as inherited
+    monstrosities. But in some few cases the loss has been gradual, and
+    {317} has been partly effected by selection, as with the rudimentary
+    combs and wattles of certain fowls. We have also seen that the wings of
+    some domesticated birds have been slightly reduced by disuse, and the
+    great reduction of the wings in certain silk-moths, with mere rudiments
+    left, has probably been aided by disuse.
+
+    With species in a state of nature, rudimentary organs are so extremely
+    common that scarcely one can be named which is wholly free from a
+    blemish of this nature. Such organs are generally variable, as several
+    naturalists have observed; for, being useless, they are not regulated
+    by natural selection, and they are more or less liable to reversion.
+    The same rule certainly holds good with parts which have become
+    rudimentary under domestication. We do not know through what steps
+    under nature rudimentary organs have passed in being reduced to their
+    present condition; but we so incessantly see in species of the same
+    group the finest gradations between an organ in a rudimentary and
+    perfect state, that we are led to believe that the passage must have
+    been extremely gradual. It may be doubted whether a change of structure
+    so abrupt as the sudden loss of an organ would ever be of service to a
+    species in a state of nature; for the conditions to which all organisms
+    are closely adapted usually change very slowly. Even if an organ did
+    suddenly disappear in some one individual by an arrest of development,
+    intercrossing with the other individuals of the same species would
+    cause it to reappear in a more or less perfect manner, so that its
+    final reduction could only be effected by the slow process of continued
+    disuse or natural selection. It is much more probable that, from
+    changed habits of life, organs first become of less and less use, and
+    ultimately superfluous; or their place may be supplied by some other
+    organ; and then disuse, acting on the offspring through inheritance at
+    corresponding periods of life, would go on reducing the organ; but as
+    most organs could be of no use at an early embryonic period, they would
+    not be affected by disuse; consequently they would be preserved at this
+    stage of growth, and would remain as rudiments. In addition to the
+    effects of disuse, the principle of economy of growth, already alluded
+    to in this chapter, would lead to the still further reduction of all
+    superfluous parts. With respect to the final and total suppression or
+    abortion of any organ, another and distinct principle, which will be
+    discussed in the chapter on pangenesis, probably takes a share in the
+    work.
+
+    With animals and plants reared by man there is no severe or recurrent
+    struggle for existence, and the principle of economy will not come into
+    action. So far, indeed, is this from being the case, that in some
+    instances organs, which are naturally rudimentary in the
+    parent-species, become partially redeveloped in the domesticated
+    descendants. Thus cows, like most other ruminants, properly have four
+    active and two rudimentary mammae; but in our domesticated animals, the
+    latter occasionally become considerably developed and yield milk. The
+    atrophied mammae, which, in male domesticated animals, including man,
+    have in some rare cases grown to full size and secreted milk, perhaps
+    offer an analogous case. The hind feet of dogs include rudiments of a
+    fifth toe, and in certain large breeds these toes, though still
+    rudimentary, become considerably developed {318} and are furnished with
+    claws. In the common Hen, the spurs and comb are rudimentary, but in
+    certain breeds these become, independently of age or disease of the
+    ovaria, well developed. The stallion has canine teeth, but the mare has
+    only traces of the alveoli, which, as I am informed by the eminent
+    veterinary Mr. G. T. Brown, frequently contain minute irregular nodules
+    of bone. These nodules, however, sometimes become developed into
+    imperfect teeth, protruding through the gums and coated with enamel;
+    and occasionally they grow to a third or even a fourth of the length of
+    the canines in the stallion. With plants I do not know whether the
+    redevelopment of rudimentary organs occurs more frequently under
+    culture than under nature. Perhaps the pear-tree may be a case in
+    point, for when wild it bears thorns, which though useful as a
+    protection are formed of branches in a rudimentary condition, but, when
+    the tree is cultivated, the thorns are reconverted into branches.
+
+Finally, though organs which must be classed as rudimentary frequently
+occur in our domesticated animals and cultivated plants, these have
+generally been formed suddenly, through an arrest of development. They
+usually differ in appearance from the rudiments which so frequently
+characterise natural species. In the latter, rudimentary organs have been
+slowly formed through continued disuse, acting by inheritance at a
+corresponding age, aided by the principle of the economy of growth, all
+under the control of natural selection. With domesticated animals, on the
+other hand, the principle of economy is far from coming into action, and
+their organs, although often slightly reduced by disuse, are not thus
+almost obliterated with mere rudiments left.
+
+       *       *       *       *       *
+
+
+{319}
+
+CHAPTER XXV.
+
+LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY.
+
+    EXPLANATION OF TERM--CORRELATION AS CONNECTED WITH
+    DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED
+    SIZE OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET
+    IN BIRDS ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE
+    HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND DERMAL
+    APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED
+    MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED
+    MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND EARS--SKULL AND CREST
+    OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTH COMPLICATED BY THE
+    ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS CORRELATED WITH
+    CONSTITUTIONAL PECULIARITIES.
+
+All the parts of the organisation are to a certain extent connected or
+correlated together; but the connexion may be so slight that it hardly
+exists, as with compound animals or the buds on the same tree. Even in the
+higher animals various parts are not at all closely related; for one part
+may be wholly suppressed or rendered monstrous without any other part of
+the body being affected. But in some cases, when one part varies, certain
+other parts always, or nearly always, simultaneously vary; they are then
+subject to the law of correlated variation. Formerly I used the somewhat
+vague expression of correlation of growth, which may be applied to many
+large classes of facts. Thus, all the parts of the body are admirably
+coordinated for the peculiar habits of life of each organic being, and they
+may be said, as the Duke of Argyll insists in his 'Reign of Law,' to be
+correlated for this purpose. Again, in large groups of animals certain
+structures always co-exist; for instance, a peculiar form of stomach with
+teeth of peculiar form, and such structures may in one sense be said to be
+correlated. But these cases have no necessary connexion with the law to be
+discussed in the present chapter; for we do not know that {320} the initial
+or primary variations of the several parts were in any way related; slight
+modifications or individual differences may have been preserved, first in
+one and then in another part, until the final and perfectly co-adapted
+structure was acquired; but to this subject I shall presently recur. Again,
+in many groups of animals the males alone are furnished with weapons, or
+are ornamented with gay colours; and these characters manifestly stand in
+some sort of correlation with the male reproductive organs, for when the
+latter are destroyed these characters disappear. But it was shown in the
+twelfth chapter that the very same peculiarity may become attached at any
+age to either sex, and afterwards be exclusively transmitted by the same
+sex at a corresponding age. In these cases we have inheritance limited by,
+or correlated with, both sex and age; but we have no reason for supposing
+that the original cause of the variation was necessarily connected with the
+reproductive organs, or with the age of the affected being.
+
+In cases of true correlated variation, we are sometimes able to see the
+nature of the connexion; but in most cases the bond is hidden from us, and
+certainly differs in different cases. We can seldom say which of two
+correlated parts first varies, and induces a change in the other; or
+whether the two are simultaneously produced by some distinct cause.
+Correlated variation is an important subject for us; for when one part is
+modified through continued selection, either by man or under nature, other
+parts of the organisation will be unavoidably modified. From this
+correlation it apparently follows that, with our domesticated animals and
+plants, varieties rarely or never differ from each other by some single
+character alone.
+
+One of the simplest cases of correlation is that a modification which
+arises during an early stage of growth tends to influence the subsequent
+development of the same part, as well as of other and intimately connected
+parts. Isidore Geoffroy St. Hilaire states[804] that this may constantly be
+observed with monstrosities {321} in the animal kingdom; and
+Moquin-Tandon[805] remarks, that, as with plants the axis cannot become
+monstrous without in some way affecting the organs subsequently produced
+from it, so axial anomalies are almost always accompanied by deviations of
+structure in the appended parts. We shall presently see that with
+short-muzzled races of the dog certain histological changes in the basal
+elements of the bones arrest their development and shorten them, and this
+affects the position of the subsequently developed molar teeth. It is
+probable that certain modifications in the larvae of insects would affect
+the structure of the mature insects. But we must be very careful not to
+extend this view too far, for, during the normal course of development,
+certain members in the same group of animals are known to pass through an
+extraordinary course of change, whilst other and closely allied members
+arrive at maturity with little change of structure.
+
+Another simple case of correlation is that with the increased or decreased
+dimensions of the whole body, or of any particular part, certain organs are
+increased or diminished in number, or are otherwise modified. Thus
+pigeon-fanciers have gone on selecting pouters for length of body, and we
+have seen that their vertebrae are generally increased in number, and their
+ribs in breadth. Tumblers have been selected for their small bodies, and
+their ribs and primary wing-feathers are generally lessened in number.
+Fantails have been selected for their large, widely-expanded tails, with
+numerous tail-feathers, and the caudal vertebrae are increased in size and
+number. Carriers have been selected for length of beak, and their tongues
+have become longer, but not in strict accordance with the length of beak.
+In this latter breed and in others having large feet, the number of the
+scutellae on the toes is greater than in the breeds with small feet. Many
+similar cases could be given. In Germany it has been observed that the
+period of gestation is longer in large-sized than in small-sized breeds of
+cattle. With our highly-improved animals of all kinds the period of
+maturity has advanced, both with respect to the full growth of the body and
+the period of reproduction; and, in correspondence with this, the teeth are
+now developed earlier than formerly, so that, {322} to the surprise of
+agriculturists, the ancient rules for judging the age of an animal by the
+state of its teeth are no longer trustworthy.[806]
+
+_Correlated Variation of Homologous Parts._--Parts which are homologous
+tend to vary in the same manner; and this is what might have been expected,
+for such parts are identical in form and structure during an early period
+of embryonic development, and are exposed in the egg or womb to similar
+conditions. The symmetry, in most kinds of animals, of the corresponding or
+homologous organs on the right and left sides of the body, is the simplest
+case in point; but this symmetry sometimes fails, as with rabbits having
+only one ear, or stags with one horn, or with many-horned sheep which
+sometimes carry an additional horn on one side of their heads. With flowers
+which have regular corollas, the petals generally vary in the same manner,
+as we see in the same complicated and elegant pattern, on the flowers of
+the Chinese pink; but with irregular flowers, though the petals are of
+course homologous, this symmetry often fails, as with the varieties of the
+_Antirrhinum_ or snapdragon, or that variety of the kidney-bean (_Phaseolus
+multiflorus_) which has a white standard-petal.
+
+In the vertebrata the front and hind limbs are homologous, and they tend to
+vary in the same manner, as we see in long and short-legged, or in thick
+and thin-legged races of the horse and dog. Isidore Geoffroy[807] has
+remarked on the tendency of supernumerary digits in man to appear, not only
+on the right and left sides, but on the upper and lower extremities. Meckel
+has insisted[808] that, when the muscles of the arm depart in number or
+arrangement from their proper type, they almost always imitate those of the
+leg; and so conversely the varying muscles of the leg imitate the normal
+muscles of the arm.
+
+In several distinct breeds of the pigeon and fowl, the legs and the two
+outer toes are heavily feathered, so that in the trumpeter pigeon they
+appear like little wings. In the feather-legged bantam the "boots" or
+feathers, which grow from the outside of the leg and generally from the two
+outer toes, have, {323} according to the excellent authority of Mr.
+Hewitt,[809] been seen to exceed the wing-feathers in length, and in one
+case were actually nine and a half inches in length! As Mr. Blyth has
+remarked to me, these leg-feathers resemble the primary wing-feathers, and
+are totally unlike the fine down which naturally grows on the legs of some
+birds, such as grouse and owls. Hence it may be suspected that excess of
+food has first given redundancy to the plumage, and then that the law of
+homologous variation has led to the development of feathers on the legs, in
+a position corresponding with those on the wing, namely, on the outside of
+the tarsi and toes. I am strengthened in this belief by the following
+curious case of correlation, which for a long time seemed to me utterly
+inexplicable, namely, that in pigeons of any breed, if the legs are
+feathered, the two outer toes are partially connected by skin. These two
+outer toes correspond with our third and fourth toes. Now, in the wing of
+the pigeon or any other bird, the first and fifth digits are wholly
+aborted; the second is rudimentary and carries the so-called
+"bastard-wing;" whilst the third and fourth digits are completely united
+and enclosed by skin, together forming the extremity of the wing. So that
+in feather-footed pigeons, not only does the exterior surface support a row
+of long feathers, like wing-feathers, but the very same digits which in the
+wing are completely united by skin become partially united by skin in the
+feet; and thus by the law of the correlated variation of homologous parts
+we can understand the curious connection of feathered legs and membrane
+between the two outer toes.
+
+Andrew Knight[810] has remarked that the face or head and the limbs vary
+together in general proportions. Compare, for instance, the head and limbs
+of a dray and race-horse, or of a greyhound and mastiff. What a monster a
+greyhound would appear with the head of a mastiff! The _modern_ bulldog,
+however, has fine limbs, but this is a recently-selected character. From
+the measurements given in the sixth chapter, we clearly see that in all the
+breeds of the pigeon the length of the beak and the size of the feet are
+correlated. The view which, as before explained, seems the most probable
+is, that disuse in all cases tends {324} to diminish the feet, the beak
+becoming at the same time through correlation shorter; but that in those
+few breeds in which length of beak has been a selected point, the feet,
+notwithstanding disuse, have through correlation increased in size.
+
+With the increased length of the beak in pigeons, not only the tongue
+increases in length, but likewise the orifice of the nostrils. But the
+increased length of the orifice of the nostrils perhaps stands in closer
+correlation with the development of the corrugated skin or wattle at the
+base of the beak; for when there is much wattle round the eyes, the eyelids
+are greatly increased or even doubled in length.
+
+There is apparently some correlation even in colour between the head and
+the extremities. Thus with horses a large white star or blaze on the
+forehead is generally accompanied by white feet.[811] With white rabbits
+and cattle, dark marks often co-exist on the tips of the ears and on the
+feet. In black and tan dogs of different breeds, tan-coloured spots over
+the eyes and tan-coloured feet almost invariably go together. These latter
+cases of connected colouring may be due either to reversion or to analogous
+variation,--subjects to which we shall hereafter return,--but this does not
+necessarily determine the question of their original correlation. If those
+naturalists are correct who maintain that the jaw-bones are homologous with
+the limb-bones, then we can understand why the head and limbs tend to vary
+together in shape and even in colour; but several highly competent judges
+dispute the correctness of this view.
+
+The lopping forwards and downwards of the immense ears of fancy rabbits is
+in part due to the disuse of the muscles, and in part to the weight and
+length of the ears, which have been increased by selection during many
+generations. Now, with the increased size and changed direction of the
+ears, not only has the bony auditory meatus become changed in outline,
+direction, and greatly in size, but the whole skull has been slightly
+modified. This could be clearly seen in "half-lops"--that is, in rabbits
+with one ear alone lopping forward--for the opposite sides of their skulls
+were not strictly symmetrical. This seems to me a curious instance of
+correlation, between hard {325} bones and organs so soft and flexible, as
+well as so unimportant under a physiological point of view, as the external
+ears. The result no doubt is largely due to mere mechanical action, that
+is, to the weight of the ears, on the same principle that the skull of a
+human infant is easily modified by pressure.
+
+The skin and the appendages of hair, feathers, hoofs, horns, and teeth, are
+homologous over the whole body. Every one knows that the colour of the skin
+and that of the hair usually vary together; so that Virgil advises the
+shepherd to look whether the mouth and tongue of the ram are black, lest
+the lambs should not be purely white. With poultry and certain ducks we
+have seen that the colour of the plumage stands in some connexion with the
+colour of the shell of the egg,--that is, with the mucous membrane which
+secretes the shell. The colour of the skin and hair, and the odour emitted
+by the glands of the skin, are said[812] to be connected, even in the same
+race of men. Generally the hair varies in the same way all over the body in
+length, fineness, and curliness. The same rule holds good with feathers, as
+we see with the laced and frizzled breeds both of fowls and pigeons. In the
+common cock the feathers on the neck and loins are always of a particular
+shape, called hackles: now in the Polish breed, both sexes are
+characterised by a tuft of feathers on the head; but through correlation
+these feathers in the male always assume the form of hackles. The wing and
+tail-feathers, though arising from parts not homologous, vary in length
+together; so that long or short winged pigeons generally have long or short
+tails. The case of the Jacobin-pigeon is more curious, for the wing and
+tail feathers are remarkably long; and this apparently has arisen in
+correlation with the elongated and reversed feathers on the back of the
+neck, which form the hood.
+
+The hoofs and hair are homologous appendages; and a careful observer,
+namely Azara,[813] states that in Paraguay horses of various colours are
+often born with their hair curled and twisted like that on the head of a
+negro. This peculiarity is strongly inherited. But what is remarkable is
+that the hoofs of these horses "are absolutely like those of a mule." The
+hair also of the mane and tail is invariably much shorter than usual, being
+only from four {326} to twelve inches in length; so that curliness and
+shortness of the hair are here, as with the negro, apparently correlated.
+
+With respect to the horns of sheep, Youatt[814] remarks that "multiplicity
+of horns is not found in any breed of much value: it is generally
+accompanied by great length and coarseness of the fleece." Several tropical
+breeds of sheep, which are clothed with hair instead of wool, have horns
+almost like those of a goat. Sturm[815] expressly declares that in
+different races the more the wool is curled the more the horns are spirally
+twisted. We have seen in the third chapter, where other analogous facts
+have been given, that the parent of the Mauchamp breed, so famous for its
+fleece, had peculiarly shaped horns. The inhabitants of Angora assert[816]
+that "only the white goats which have horns wear the fleece in the long
+curly locks that are so much admired; those which are not horned having a
+comparatively close coat." From these cases we may conclude that the hair
+or wool and the horns vary in a correlated manner. Those who have tried
+hydropathy are aware that the frequent application of cold water stimulates
+the skin; and whatever stimulates the skin tends to increase the growth of
+the hair, as is well shown in the abnormal growth of hair near old inflamed
+surfaces. Now, Professor Low[817] is convinced that with the different
+races of British cattle thick skin and long hair depend on the humidity of
+the climate which they inhabit. We can thus see how a humid climate might
+act on the horns--in the first place directly on the skin and hair, and
+secondly by correlation on the horns. The presence or absence of horns,
+moreover, both in the case of sheep and cattle, acts, as will presently be
+shown, by some sort of correlation on the skull.
+
+With respect to hair and teeth, Mr. Yarrell[818] found many of the teeth
+deficient in three hairless "_Aegyptian_" dogs, and in a hairless terrier.
+The incisors, canines, and premolars suffered most, but in one case all the
+teeth, except the large tubercular molar on each side, were deficient. With
+man several striking cases have been recorded[819] of inherited baldness
+with {327} inherited deficiency, either complete or partial, of the teeth.
+We see the same connexion in those rare cases in which the hair has been
+renewed in old age, for this has "usually been accompanied by a renewal of
+the teeth." I have remarked in a former part of this volume that the great
+reduction in the size of the tusks in domestic boars probably stands in
+close relation with their diminished bristles, due to a certain amount of
+protection; and that the reappearance of the tusks in boars, which have
+become feral and are fully exposed to the weather, probably depends on the
+reappearance of the bristles. I may add, though not strictly connected with
+our present point, that an agriculturist[820] asserts that "pigs with
+little hair on their bodies are most liable to lose their tails, showing a
+weakness of the tegumental structure. It may be prevented by crossing with
+a more hairy breed."
+
+In the previous cases deficient hair, and teeth deficient in number or
+size, are apparently connected. In the following cases abnormally redundant
+hair, and teeth either deficient or redundant, are likewise connected. Mr.
+Crawfurd[821] saw at the Burmese Court a man, thirty years old, with his
+whole body, except the hands and feet, covered with straight silky hair,
+which on the shoulders and spine was five inches in length. At birth the
+ears alone were covered. He did not arrive at puberty, or shed his milk
+teeth, until twenty years old; and at this period he acquired five teeth in
+the upper jaw, namely four incisors and one canine, and four incisor teeth
+in the lower jaw; all the teeth were small. This man had a daughter, who
+was born with hair within her ears; and the hair soon extended over her
+body. When Captain Yule[822] visited the Court, he found this girl grown
+up; and she presented a strange appearance with even her nose densely
+covered with soft hair. Like her father, she was furnished with incisor
+teeth alone. The King had with difficulty bribed a man to marry her, and of
+her two children, one, a boy fourteen months old, had hair growing out of
+his ears, with a beard and moustache. This strange peculiarity had,
+therefore, been inherited for three generations, with the molar teeth
+deficient in the grandfather and mother; whether {328} these teeth would
+likewise fail in the infant could not be told. Here is another case
+communicated to me by Mr. Wallace on the authority of Dr. Purland, a
+dentist: Julia Pastrana, a Spanish dancer, was a remarkably fine woman, but
+she had a thick masculine beard and a hairy forehead; she was photographed,
+and her stuffed skin was exhibited as a show; but what concerns us is, that
+she had in both the upper and lower jaw an irregular double set of teeth,
+one row being placed within the other, of which Dr. Purland took a cast.
+From the redundancy of the teeth her mouth projected, and her face had a
+gorilla-like appearance. These cases and those of the hairless dogs
+forcibly call to mind the fact, that the two orders of mammals--namely, the
+Edentata and Cetacea--which are the most abnormal in their dermal covering,
+are likewise the most abnormal either by deficiency or redundancy of teeth.
+
+The organs of sight and hearing are generally admitted to be homologous,
+both with each other and with the various dermal appendages; hence these
+parts are liable to be abnormally affected in conjunction. Mr. White Cowper
+says "that in all cases of double microphthalmia brought under his notice
+he has at the same time met with defective development of the dental
+system." Certain forms of blindness seem to be associated with the colour
+of the hair; a man with black hair and a woman with light-coloured hair,
+both of sound constitution, married and had nine children, all of whom were
+born blind; of these children, five "with dark hair and brown iris were
+afflicted with amaurosis; the four others, with light-coloured hair and
+blue iris, had amaurosis and cataract conjoined." Several cases could be
+given, showing that some relation exists between various affections of the
+eyes and ears; thus Liebreich states that out of 241 deaf-mutes in Berlin,
+no less than fourteen suffered from the rare disease called pigmentary
+retinitis. Mr. White Cowper and Dr. Earle have remarked that inability to
+distinguish different colours, or colour-blindness, "is often associated
+with a corresponding inability to distinguish musical sounds."[823]
+
+{329}
+
+Here is a more curious case: white cats, if they have blue eyes, are almost
+always deaf. I formerly thought that the rule was invariable, but I have
+heard of a few authentic exceptions. The first two notices were published
+in 1829, and relate to English and Persian cats: of the latter, the Rev.
+W. T. Bree possessed a female, and he states "that of the offspring
+produced at one and the same birth, such as, like the mother, were entirely
+white (with blue eyes) were, like her, invariably deaf; while those that
+had the least speck of colour on their fur, as invariably possessed the
+usual faculty of hearing."[824] The Rev. W. Darwin Fox informs me that he
+has seen more than a dozen instances of this correlation in English,
+Persian, and Danish cats; but he adds "that, if one eye, as I have several
+times observed, be not blue, the cat hears. On the other hand, I have never
+seen a white cat with eyes of the common colour that was deaf." In France
+Dr. Sichel[825] has observed during twenty years similar facts; he adds the
+remarkable case of the iris beginning, at the end of four months, to grow
+dark-coloured, and then the cat first began to hear.
+
+This case of correlation in cats has struck many persons as marvellous.
+There is nothing unusual in the relation between blue eyes and white fur;
+and we have already seen that the organs of sight and hearing are often
+simultaneously affected. In the present instance the cause probably lies in
+a slight arrest of development in the nervous system in connection with the
+sense-organs. Kittens during the first nine days, whilst their eyes are
+closed, appear to be completely deaf; I have made a great clanging noise
+with a poker and shovel close to their heads, both when they were asleep
+and awake, without producing any effect. The trial must not be made by
+shouting close to their ears, for they are, even when asleep, extremely
+sensitive to a breath of air. Now, as long as the eyes continue closed, the
+iris is no doubt blue, for in all the kittens which I have seen this colour
+remains for some time after the eyelids open. Hence, if we suppose the
+development of the organs of sight and hearing to be arrested at the stage
+of the closed eyelids, the eyes would {330} remain permanently blue and the
+ears would be incapable of perceiving sound; and we should thus understand
+this curious case. As, however, the colour of the fur is determined long
+before birth, and as the blueness of the eyes and the whiteness of the fur
+are obviously connected, we must believe that some primary cause acts at an
+early period.
+
+The instances of correlated variability hitherto given have been chiefly
+drawn from the animal kingdom, and we will now turn to plants. Leaves,
+sepals, petals, stamens, and pistils are all homologous. In double flowers
+we see that the stamens and pistils vary in the same manner, and assume the
+form and colour of the petals. In the double columbine (_Aquilegia
+vulgaris_), the successive whorls of stamens are converted into
+cornucopias, which are enclosed within each other and resemble the petals.
+In hose-and-hose flowers the sepals mock the petals. In some cases the
+flowers and leaves vary together in tint: in all the varieties of the
+common pea, which have purple flowers, a purple mark may be seen on the
+stipules. In other cases the leaves and fruit and seeds vary together in
+colour, as in a curious pale-leaved variety of the sycamore, which has
+recently been described in France,[826] and as in the purple-leaved hazel,
+in which the leaves, the husk of the nut, and the pellicle round the kernel
+are all coloured purple.[827] Pomologists can predict to a certain extent,
+from the size and appearance of the leaves of their seedlings, the probable
+nature of the fruit; for, as Van Mons remarks,[828] variations in the
+leaves are generally accompanied by some modification in the flower, and
+consequently in the fruit. In the Serpent melon, which has a narrow
+tortuous fruit above a yard in length, the stem of the plant, the peduncle
+of the female flower, and the middle lobe of the leaf, are all elongated in
+a remarkable manner. On the other hand, several varieties of Cucurbita,
+which have dwarfed stems, all produce, as Naudin remarks with surprise,
+leaves of the same peculiar shape. Mr. G. Maw informs me that all the
+varieties of the scarlet Pelargoniums which have contracted or imperfect
+leaves have contracted flowers: the difference between {331} "Brilliant"
+and its parent "Tom Thumb" is a good instance of this. It may be suspected
+that the curious case described by Risso,[829] of a variety of the Orange
+which produces on the young shoots rounded leaves with winged petioles, and
+afterwards elongated leaves on long but wingless petioles, is connected
+with the remarkable change in form and nature which the fruit undergoes
+during its development.
+
+In the following instance we have the colour and form of the petals
+apparently correlated, and both dependent on the nature of the season. An
+observer, skilled in the subject, writes,[830] "I noticed, during the year
+1842, that every Dahlia, of which the colour had any tendency to scarlet,
+was deeply notched--indeed to so great an extent as to give the petals the
+appearance of a saw; the indentures were, in some instances, more than a
+quarter of an inch deep." Again, Dahlias which have their petals tipped
+with a different colour from the rest are very inconstant, and during
+certain years some, or even all the flowers, become uniformly coloured; and
+it has been observed with several varieties,[831] that when this happens
+the petals grow much elongated and lose their proper shape. This, however,
+may be due to reversion, both in colour and form, to the aboriginal
+species.
+
+       *       *       *       *       *
+
+In this discussion on correlation, we have hitherto treated of cases in
+which we can partly understand the bond of connexion; but I will now give
+cases in which we cannot even conjecture, or can only very obscurely see,
+what is the nature of the bond. Isidore Geoffroy St. Hilaire, in his work
+on Monstrosities, insists,[832] "que certaines anomalies coexistent
+rarement entr'elles, d'autres frequemment, d'autres enfin presque
+constamment, malgre la difference tres-grande de leur nature, et
+quoiqu'elles puissent paraitre _completement independantes_ les unes des
+autres." We see something analogous in certain diseases: thus I hear from
+Mr. Paget that in a rare affection of the {332} renal capsules (of which
+the functions are unknown), the skin becomes bronzed; and in hereditary
+syphilis, both the milk and the second teeth assume a peculiar and
+characteristic form. Professor Rolleston, also, informs me that the incisor
+teeth are sometimes furnished with a vascular rim in correlation with
+intra-pulmonary deposition of tubercles. In other cases of phthisis and of
+cyanosis the nails and finger-ends become clubbed like acorns. I believe
+that no explanation has been offered of these and of many other cases of
+correlated disease.
+
+What can be more curious and less intelligible than the fact previously
+given, on the authority of Mr. Tegetmeier, that young pigeons of all
+breeds, which when mature have white, yellow, silver-blue, or dun-coloured
+plumage, come out of the egg almost naked; whereas pigeons of other colours
+when first born are clothed with plenty of down? White Pea-fowls, as has
+been observed both in England and France,[833] and as I have myself seen,
+are inferior in size to the common coloured kind; and this cannot be
+accounted for by the belief that albinism is always accompanied by
+constitutional weakness; for white or albino moles are generally larger
+than the common kind.
+
+To turn to more important characters: the niata cattle of the Pampas are
+remarkable from their short foreheads, upturned muzzles, and curved lower
+jaws. In the skull the nasal and premaxillary bones are much shortened, the
+maxillaries are excluded from any junction with the nasals, and all the
+bones are slightly modified, even to the plane of the occiput. From the
+analogical case of the dog, hereafter to be given, it is probable that the
+shortening of the nasal and adjoining bones is the proximate cause of the
+other modifications in the skull, including the upward curvature of the
+lower jaw, though we cannot follow out the steps by which these changes
+have been effected.
+
+Polish fowls have a large tuft of feathers on their heads; and their skulls
+are perforated by numerous holes, so that a pin can be driven into the
+brain without touching any bone. That this deficiency of bone is in some
+way connected with the tuft of feathers is clear from tufted ducks and
+geese likewise having {333} perforated skulls. The case would probably be
+considered by some authors as one of balancement or compensation. In the
+chapter on Fowls, I have shown that with Polish fowls the tuft of feathers
+was probably at first small; by continued selection it became larger, and
+then rested on a fleshy or fibrous mass; and finally, as it became still
+larger, the skull itself became more and more protuberant until it acquired
+its present extraordinary structure. Through correlation with the
+protuberance of the skull, the shape and even the relative connexion of the
+premaxillary and nasal bones, the shape of the orifice of the nostrils, the
+breadth of the frontal bone, the shape of the post-lateral processes of the
+frontal and squamosal bones, and the direction of the bony cavity of the
+ear, have all been modified. The internal configuration of the skull and
+the whole shape of the brain have likewise been altered in a truly
+marvellous manner.
+
+After this case of the Polish fowl it would be superfluous to do more than
+refer to the details previously given on the manner in which the changed
+form of the comb, in various breeds of the fowl, has affected the skull,
+causing by correlation crests, protuberances, and depressions on its
+surface.
+
+With our cattle and sheep the horns stand in close connexion with the size
+of the skull, and with the shape of the frontal bones; thus Cline[834]
+found that the skull of a horned ram weighed five times as much as that of
+a hornless ram of the same age. When cattle become hornless, the frontal
+bones are "materially diminished in breadth towards the poll;" and the
+cavities between the bony plates "are not so deep, nor do they extend
+beyond the frontals."[835]
+
+       *       *       *       *       *
+
+It may be well here to pause and observe how the effects of correlated
+variability, of the increased use of parts, and of the accumulation through
+natural selection of so-called spontaneous variations, are in many cases
+inextricably commingled. We may borrow an illustration from Mr. Herbert
+Spencer, who remarks that, when the Irish elk acquired its gigantic horns,
+weighing above one hundred pounds, numerous co-ordinated {334} changes of
+structure would have been indispensable,--namely, a thickened skull to
+carry the horns; strengthened cervical vertebrae, with strengthened
+ligaments; enlarged dorsal vertebrae to support the neck, with powerful
+fore-legs and feet; all these parts being supplied with proper muscles,
+blood-vessels, and nerves. How then could these admirably co-ordinated
+modifications of structure have been acquired? According to the doctrine
+which I maintain, the horns of the male elk were slowly gained through
+sexual selection,--that is, by the best-armed males conquering the
+worse-armed, and leaving a greater number of descendants. But it is not at
+all necessary that the several parts of the body should have simultaneously
+varied. Each stag presents individual differences, and in the same district
+those which had slightly heavier horns, or stronger necks, or stronger
+bodies, or were the most courageous, would secure the greater number of
+does, and consequently leave a greater number of offspring. The offspring
+would inherit, in a greater or less degree, these same qualities, would
+occasionally intercross with each other, or with other individuals varying
+in some favourable manner; and of their offspring, those which were the
+best endowed in any respect would continue multiplying; and so onwards,
+always progressing, sometimes in one direction, and sometimes in another,
+towards the present excellently co-ordinated structure of the male elk. To
+make this clear, let us reflect on the probable steps, as shown in the
+twentieth chapter, by which our race and dray-horses have arrived at their
+present state of excellence; if we could view the whole series of
+intermediate forms between one of these animals and an early unimproved
+progenitor, we should behold a vast number of animals, not equally improved
+in each generation throughout their entire structure, but sometimes a
+little more in one point, and sometimes in another, yet on the whole
+gradually approaching in character to our present race or dray-horses,
+which are so admirably fitted in the one case for fleetness and in the
+other for draught.
+
+Although natural selection would thus[836] tend to give to the {335} male
+elk its present structure, yet it is probable that the inherited influence
+of use has played an equal or more important part. As the horns gradually
+increased in weight, the muscles of the neck, with the bones to which they
+are attached, would increase in size and strength; and these parts would
+react on the body and legs. Nor must we overlook the fact that certain
+parts of the skull and the extremities would, judging by analogy, tend from
+the first to vary in a correlated manner. The increased weight of the horns
+would also act directly on the skull, in the same manner as, when one bone
+is removed in the leg of a dog, the other bone, which has to carry the
+whole weight of the body, increases in thickness. But from the facts given
+with respect to horned and hornless cattle, it is probable that the horns
+and skull would immediately act on each other through the principle of
+correlation. Lastly, the growth and subsequent wear and tear of the
+augmented muscles and bones would require an increased supply of blood, and
+consequently an increased supply of food; and this again would require
+increased powers of mastication, digestion, respiration, and excretion.
+
+_Colour as Correlated with Constitutional Peculiarities._
+
+It is an old belief that with man there is a connexion between complexion
+and constitution; and I find that some of the best authorities believe in
+this to the present day.[837] Thus Dr. Beddoe by his tables shows[838] that
+a relation exists between liability to consumption and the colour of the
+hair, eyes, and skin. It has been affirmed[839] that, in the French army
+which invaded Russia, soldiers having a dark complexion, from the {336}
+southern parts of Europe, withstood the intense cold better than those with
+lighter complexions from the north; but no doubt such statements are liable
+to error.
+
+In the second chapter on Selection I have given several cases proving that
+with animals and plants differences in colour are correlated with
+constitutional differences, as shown by greater or less immunity from
+certain diseases, from the attacks of parasitic plants and animals, from
+burning by the sun, and from the action of certain poisons. When all the
+individuals of any one variety possess an immunity of this nature, we
+cannot feel sure that it stands in any sort of correlation with their
+colour; but when several varieties of the same species, which are similarly
+coloured, are thus characterised, whilst other coloured varieties are not
+thus favoured, we must believe in the existence of a correlation of this
+kind. Thus in the United States purple-fruited plums of many kinds are far
+more affected by a certain disease than green or yellow-fruited varieties.
+On the other hand, yellow-fleshed peaches of various kinds suffer from
+another disease much more than the white-fleshed varieties. In the
+Mauritius red sugar-canes are much less affected by a particular disease
+than the white canes. White onions and verbenas are the most liable to
+mildew; and in Spain the green-fruited grapes suffered from the
+vine-disease more than other coloured varieties. Dark-coloured pelargoniums
+and verbenas are more scorched by the sun than varieties of other colours.
+Red wheats are believed to be hardier than white; whilst red-flowered
+hyacinths were more injured during one particular winter in Holland than
+other coloured varieties. With animals, white terriers suffer most from the
+distemper, white chickens from a parasitic worm in their tracheae, white
+pigs from scorching by the sun, and white cattle from flies; but the
+caterpillars of the silk-moth which yield white cocoons suffered in France
+less from the deadly parasitic fungus than those producing yellow silk.
+
+The cases of immunity from the action of certain vegetable poisons, in
+connexion with colour, are more interesting, and are at present wholly
+inexplicable. I have already given a remarkable instance, on the authority
+of Professor Wyman, of all the hogs, excepting those of a black colour,
+suffering severely in Virginia from eating the root of the _Lachnanthes
+tinctoria_. {337} According to Spinola and others,[840] buckwheat
+(_Polygonum fagopyrum_), when in flower, is highly injurious to white or
+white-spotted pigs, if they are exposed to the heat of the sun, but is
+quite innocuous to black pigs. By two accounts, the _Hypericum crispum_ in
+Sicily is poisonous to white sheep alone; their heads swell, their wool
+falls off, and they often die; but this plant, according to Lecce, is
+poisonous only when it grows in swamps; nor is this improbable, as we know
+how readily the poisonous principle in plants is influenced by the
+conditions under which they grow.
+
+Three accounts have been published in Eastern Prussia, of white and
+white-spotted horses being greatly injured by eating mildewed and
+honeydewed vetches; every spot of skin bearing white hairs becoming
+inflamed and gangrenous. The Rev. J. Rodwell informs me that his father
+turned out about fifteen cart-horses into a field of tares which in parts
+swarmed with black aphides, and which no doubt were honeydewed, and
+probably mildewed; the horses, with two exceptions, were chesnuts and bays
+with white marks on their faces and pasterns, and the white parts alone
+swelled and became angry scabs. The two bay horses with no white marks
+entirely escaped all injury. In Guernsey, when horses eat fools' parsley
+(_Aethusa cynapium_) they are sometimes violently purged; and this plant
+"has a peculiar effect on the nose and lips, causing deep cracks and
+ulcers, particularly on horses with white muzzles."[841] With cattle,
+independently of the action of any poison, cases have been published by
+Youatt and Erdt of cutaneous diseases with much constitutional disturbance
+(in one instance after exposure to a hot sun) affecting every single point
+which bore a white hair, but completely passing over other parts of the
+body. Similar cases have been observed with horses.[842]
+
+We thus see that not only do those parts of the skin which bear white hair
+differ in a remarkable manner from those bearing {338} hair of any other
+colour, but that in addition some great, constitutional difference must
+stand in correlation with the colour of the hair; for in the
+above-mentioned cases, vegetable poisons caused fever, swelling of the
+head, as well as other symptoms, and even death, to all the white or
+white-spotted animals.
+
+       *       *       *       *       *
+
+
+{339}
+
+CHAPTER XXVI.
+
+LAWS OF VARIATION, _continued_--SUMMARY.
+
+    ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OF
+    MULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICAL
+    PRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THE
+    PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS OR
+    PARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS.
+
+_On the Affinity of Homologous Parts._--This law was first generalised by
+Geoffroy Saint Hilaire, under the expression of _La loi de l'affinite de
+soi pour soi_. It has been fully discussed and illustrated by his son,
+Isidore Geoffroy, with respect to monsters in the animal kingdom,[843] and
+by Moquin-Tandon, with respect to monstrous plants. When similar or
+homologous parts, whether belonging to the same embryo or to two distinct
+embryos, are brought during an early stage of development into contact,
+they often blend into a single part or organ; and this complete fusion
+indicates some mutual affinity between the parts, otherwise they would
+simply cohere. Whether any power exists which tends to bring homologous
+parts into contact seems more doubtful. The tendency to complete fusion is
+not a rare or exceptional fact. It is exhibited in the most striking manner
+by double monsters. Nothing can be more extraordinary than the manner, as
+shown in various published plates, in which the corresponding parts of two
+embryos become intimately fused together. This is perhaps best seen in
+monsters with two heads, which are united, summit to summit, or face to
+face, or, Janus-like, back to back, or obliquely side to side. In one
+instance of two heads united almost face to face, but a little obliquely,
+four ears were developed, and on one side a perfect face, which was
+manifestly formed by the union of two {340} half-faces. Whenever two bodies
+or two heads are united, each bone, muscle, vessel, and nerve on the line
+of junction seems to seek out its fellow, and becomes completely fused with
+it. Lereboullet,[844] who carefully studied the development of double
+monsters in fishes, observed in fifteen instances the steps by which two
+heads gradually became fused into one. In this and other such cases, no
+one, I presume, supposes that the two already formed heads actually blend
+together, but that the corresponding parts of each head grow into one
+during the further progress of development, accompanied as it always is
+with incessant absorption and renovation. Double monsters were formerly
+thought to be formed by the union of two originally distinct embryos
+developed upon distinct vitelli; but now it is admitted that "their
+production is due to the spontaneous divarication of the embryonic mass
+into two halves;"[845] this, however, is effected by different methods. But
+the belief that double monsters originate from the division of one germ,
+does not necessarily affect the question of subsequent fusion, or render
+less true the law of the affinity of homologous parts.
+
+The cautious and sagacious J. Mueller,[846] when speaking of Janus-like
+monsters, says, that "without the supposition that some kind of affinity or
+attraction is exerted between corresponding parts, unions of this kind are
+inexplicable." On the other hand, Vrolik, and he is followed by others,
+disputes this conclusion, and argues from the existence of a whole series
+of monstrosities, graduating from a perfectly double monster to a mere
+rudiment of an additional digit, that "an excess of formative power" is the
+cause and origin of every monstrous duplicity. That there are two distinct
+classes of cases, and that parts may be doubled independently of the
+existence of two embryos, is certain; for a single embryo, or even a single
+adult animal, may produce doubled organs. Thus Valentin, as quoted by
+Vrolik, injured the caudal extremity of an embryo, and three days
+afterwards it produced rudiments of a double pelvis and of double hind
+limbs. {341} Hunter and others have observed lizards with their tails
+reproduced and doubled. When Bonnet divided longitudinally the foot of the
+salamander, several additional digits were occasionally formed. But neither
+these cases, nor the perfect series from a double monster to an additional
+digit, seem to me opposed to the belief that corresponding parts have a
+mutual affinity, and consequently tend to fuse together. A part may be
+doubled and remain in this state, or the two parts thus formed may
+afterwards through the law of affinity become blended; or two homologous
+parts in two separate embryos may, through the same principle, unite and
+form a single part.
+
+The law of the affinity and fusion of similar parts applies to the
+homologous organs of the same individual animal, as well as to double
+monsters. Isidore Geoffroy gives a number of instances of two or more
+digits, of two whole legs, of two kidneys, and of several teeth becoming
+symmetrically fused together in a more or less perfect manner. Even the two
+eyes have been known to unite into a single eye, forming a cyclopean
+monster, as have the two ears, though naturally standing so far apart. As
+Geoffroy remarks, these facts illustrate in an admirable manner the normal
+fusion of various organs which during an early embryonic period are double,
+but which afterwards always unite into a single median organ. Organs of
+this nature are generally found in a permanently double condition in other
+members of the same class. These cases of normal fusion appear to me to
+afford the strongest support in favour of the present law. Adjoining parts
+which are not homologous sometimes cohere; but this cohesion appears to
+result from mere juxtaposition, and not from mutual affinity.
+
+In the vegetable kingdom Moquin-Tandon[847] gives a long list of cases,
+showing how frequently homologous parts, such as leaves, petals, stamens,
+and pistils, as well as aggregates of homologous parts, such as buds,
+flowers, and fruit, become blended into each other with perfect symmetry.
+It is interesting to examine a compound flower of this nature, formed of
+exactly double the proper number of sepals, petals, stamens, and pistils,
+with each whorl of organs circular, and with no trace left of the {342}
+process of fusion. The tendency in homologous parts to unite during their
+early development, Moquin-Tandon considers as one of the most striking laws
+governing the production of monsters. It apparently explains a multitude of
+cases, both in the animal and vegetable kingdoms; it throws a clear light
+on many normal structures which have evidently been formed by the union of
+originally distinct parts, and it possesses, as we shall see in a future
+chapter, much theoretical interest.
+
+       *       *       *       *       *
+
+_On the Variability of Multiple and Homologous Parts._--Isidore
+Geoffroy[848] insists that, when any part or organ is repeated many times
+in the same animal, it is particularly liable to vary both in number and
+structure. With respect to number, the proposition may, I think, be
+considered as fully established; but the evidence is chiefly derived from
+organic beings living under their natural conditions, with which we are not
+here concerned. When the vertebrae, or teeth, or rays in the fins of
+fishes, or feathers in the tails of birds, or petals, stamens, pistils, and
+seeds in plants, are very numerous, the number is generally variable. The
+explanation of this simple fact is by no means obvious. With respect to the
+variability in structure of multiple parts, the evidence is not so
+decisive; but the fact, as far as it may be trusted, probably depends on
+multiple parts being of less physiological importance than single parts;
+consequently their perfect standard of structure has been less rigorously
+enforced by natural selection.
+
+       *       *       *       *       *
+
+_Compensation of Growth, or Balancement._--This law, as applied to natural
+species, was propounded by Goethe and Geoffroy St. Hilaire at nearly the
+same time. It implies that, when much organised matter is used in building
+up some one part, other parts are starved and become reduced. Several
+authors, especially botanists, believe in this law; others reject it. As
+far as I can judge, it occasionally holds good; but its importance has
+probably been exaggerated. It is scarcely possible to distinguish between
+the supposed effects of such compensation of growth, and the effects of
+long-continued selection, which {343} may at the same time lead to the
+augmentation of one part and the diminution of another. There can be no
+doubt that an organ may be greatly increased without any corresponding
+diminution in the adjoining parts. To recur to our former illustration of
+the Irish elk, it may be asked what part has suffered in consequence of the
+immense development of the horns?
+
+It has already been observed that the struggle for existence does not bear
+hard on our domesticated productions; consequently the principle of economy
+of growth will seldom affect them, and we ought not to expect to find
+frequent evidence of compensation. We have, however, some such cases.
+Moquin-Tandon describes a monstrous bean,[849] in which the stipules were
+enormously developed, and the leaflets apparently in consequence completely
+aborted; this case is interesting, as it represents the natural condition
+of _Lathyrus aphaca_, with its stipules of great size, and its leaves
+reduced to mere threads, which act as tendrils. De Candolle[850] has
+remarked that the varieties of _Raphanus sativus_ which have small roots
+yield numerous seed, valuable from containing oil, whilst those with large
+roots are not productive in this latter respect; and so it is with
+_Brassica asperifolia_. The varieties of the potato which produce tubers
+very early in the season rarely bear flowers; but Andrew Knight,[851] by
+checking the growth of the tubers, forced the plants to flower. The
+varieties of _Cucurbita pepo_ which produce large fruit yield, according to
+Naudin, few in number; whilst those producing small fruit yield a vast
+number. Lastly, I have endeavoured to show in the eighteenth chapter that
+with many cultivated plants unnatural treatment checks the full and proper
+action of the reproductive organs, and they are thus rendered more or less
+sterile; consequently, in the way of compensation, the fruit becomes
+greatly enlarged, and, in double flowers, the petals are greatly increased
+in number.
+
+With animals, it has been found difficult to produce cows which should
+first yield much milk, and afterwards be capable of {344} fattening well.
+With fowls which have large topknots and beards the comb and wattles are
+generally much reduced in size. Perhaps the entire absence of the oil-gland
+in fantail pigeons may be connected with the great development of their
+tails.
+
+       *       *       *       *       *
+
+_Mechanical Pressure as a Cause of Modifications._--In some few cases there
+is reason to believe that mere mechanical pressure has affected certain
+structures. Every one knows that savages alter the shape of their infants'
+skulls by pressure at an early age; but there is no reason to believe that
+the result is ever inherited. Nevertheless Vrolik and Weber[852] maintain
+that the shape of the human head is influenced by the shape of the mother's
+pelvis. The kidneys in different birds differ much in form, and St.
+Ange[853] believes that this is determined by the form of the pelvis, which
+again, no doubt, stands in close relation with their various habits of
+locomotion. In snakes, the viscera are curiously displaced, in comparison
+with their position in other vertebrates; and this has been attributed by
+some authors to the elongation of their bodies; but here, as in so many
+previous cases, it is impossible to disentangle any direct result of this
+kind from that consequent on natural selection. Godron has argued[854] that
+the normal abortion of the spur on the inner side of the flower in
+Corydalis, is caused by the buds being closely pressed at a very early
+period of growth, whilst under ground, against each other and against the
+stem. Some botanists believe that the singular difference in the shape both
+of the seed and corolla, in the interior and exterior florets in certain
+compositous and umbelliferous plants, is due to the pressure to which the
+inner florets are subjected; but this conclusion is doubtful.
+
+The facts just given do not relate to domesticated productions, and
+therefore do not strictly concern us. But here is a more appropriate case:
+H. Mueller[855] has shown that in {345} short-faced races of the dog some
+of the molar teeth are placed in a slightly different position from that
+which they occupy in other dogs, especially in those having elongated
+muzzles; and as he remarks, any inherited change in the arrangement of the
+teeth deserves notice, considering their classificatory importance. This
+difference in position is due to the shortening of certain facial bones,
+and the consequent want of space; and the shortening results from a
+peculiar and abnormal state of the basal cartilages of the bones.
+
+_Relative Position of Flowers with respect to the Axis, and of Seeds in the
+Capsule, as inducing Variation._
+
+    In the thirteenth chapter various peloric flowers were described, and
+    their production was shown to be due either to arrested development, or
+    to reversion to a primordial condition. Moquin-Tandon has remarked that
+    the flowers which stand on the summit of the main stem or of a lateral
+    branch are more liable to become peloric than those on the sides;[856]
+    and he adduces, amongst other instances, that of _Teucrium
+    campanulatum_. In another Labiate plant grown by me, viz. the
+    _Galeobdolon luteum_, the peloric flowers were always produced on the
+    summit of the stem, where flowers are not usually borne. In
+    Pelargonium, a _single_ flower in the truss is frequently peloric, and
+    when this occurs I have during several years invariably observed it to
+    be the central flower. This is of such frequent occurrence that one
+    observer[857] gives the names of ten varieties flowering at the same
+    time, in every one of which the central flower was peloric.
+    Occasionally more than one flower in the truss is peloric, and then of
+    course the additional ones must be lateral. These flowers are
+    interesting as showing how the whole structure is correlated. In the
+    common Pelargonium the upper sepal is produced into a nectary which
+    coheres with the flower-peduncle; the two upper petals differ a little
+    in shape from the three lower ones, and are marked with dark shades of
+    colour; the stamens are graduated in length and upturned. In the
+    peloric flowers, the nectary aborts; all the petals become alike both
+    in shape and colour; the stamens are generally reduced in number and
+    become straight, so that the whole flower resembles that of the allied
+    genus Erodium. The correlation between these changes is well shown when
+    one of the two upper petals alone loses its dark mark, for in this case
+    the nectary does not entirely abort, but is usually much reduced in
+    length.[858]
+
+    {346}
+
+    Morren has described[859] a marvellous flask-shaped flower of the
+    Calceolaria, nearly four inches in length, which was almost completely
+    peloric; it grew on the summit of the plant, with a normal flower on
+    each side; Prof. Westwood also has described[860] three similar peloric
+    flowers, which all occupied a central position on the flower-branches.
+    In the Orchideous genus, Phalaenopsis, the terminal flower has been
+    seen to become peloric.
+
+    In a Laburnum-tree I observed that about a fourth part of the racemes
+    produced terminal flowers which had lost their papilionaceous
+    structure. These were produced after almost all the other flowers on
+    the same racemes had withered. The most perfectly pelorised examples
+    had six petals, each marked with black striae like those on the
+    standard-petal. The keel seemed to resist the change more than the
+    other petals. Dutrochet has described[861] an exactly similar case in
+    France, and I believe these are the only two instances of pelorism in
+    the laburnum which have been recorded. Dutrochet remarks that the
+    racemes on this tree do not properly produce a terminal flower, so
+    that, as in the case of the Galeobdolon, their position as well as
+    their structure are both anomalies, which no doubt are in some manner
+    related. Dr. Masters has briefly described another leguminous
+    plant,[862] namely, a species of clover, in which the uppermost and
+    central flowers were regular or had lost their papilionaceous
+    structure. In some of these plants the flower-heads were also
+    proliferous.
+
+    Lastly, Linaria produces two kinds of peloric flowers, one having
+    simple petals, and the other having them all spurred. The two forms, as
+    Naudin remarks,[863] not rarely occur on the same plant, but in this
+    case the spurred form almost invariably stands on the summit of the
+    spike.
+
+    The tendency in the terminal or central flower to become peloric more
+    frequently than other flowers, probably results from "the bud which
+    stands on the end of a shoot receiving the most sap; it grows out into
+    a stronger shoot than those situated lower down."[864] I have discussed
+    the connection between pelorism and a central position, partly because
+    some few plants are known normally to produce a terminal flower
+    different in structure from the lateral ones; but chiefly on account of
+    the following case, in which we see a tendency to variability or to
+    reversion connected with the same position. A great judge of
+    Auriculas[865] states that when an Auricula throws up a side bloom it
+    is pretty sure to keep its character; but that if it grows from the
+    centre or heart of the plant, whatever the colour of the edging ought
+    to be, "it is just as likely to come in any other class as in the one
+    to which it properly belongs." This is so notorious a {347} fact, that
+    some florists regularly pinch off the central trusses of flowers.
+    Whether in the highly improved varieties the departure of the central
+    trusses from their proper type is due to reversion, I do not know. Mr.
+    Dombrain insists that, whatever may be the commonest kind of
+    imperfection in each variety, this is generally exaggerated in the
+    central truss. Thus one variety "sometimes has the fault of producing a
+    little green floret in the centre of the flower," and in central blooms
+    these become excessive in size. In some central blooms, sent to me by
+    Mr. Dombrain, all the organs of the flower were rudimentary in
+    structure, of minute size, and of a green colour, so that by a little
+    further change all would have been converted into small leaves. In this
+    case we clearly see a tendency to prolification--a term which, I may
+    explain to those who have never attended to botany, means the
+    production of a branch or flower, or head of flowers, out of another
+    flower. Now Dr. Masters[866] states that the central or uppermost
+    flower on a plant is generally the most liable to prolification. Thus,
+    in the varieties of the Auricula, the loss of their proper character
+    and a tendency to prolification, and in other plants a tendency to
+    prolification and pelorism, are all connected together, and are due
+    either to arrested development, or to reversion to a former condition.
+
+    The following is a more interesting case; Metzger[867] cultivated in
+    Germany several kinds of maize brought from the hotter parts of
+    America, and he found, as has been previously described, that in two or
+    three generations the grains became greatly changed in form, size, and
+    colour; and with respect to two races he expressly states that in the
+    first generation, whilst the lower grains on each head retained their
+    proper character, the uppermost grains already began to assume that
+    character which in the third generation all the grains acquired. As we
+    do not know the aboriginal parent of the maize, we cannot tell whether
+    these changes are in any way connected with reversion.
+
+    In the two following cases, reversion, as influenced by the position of
+    the seed in the capsule, evidently acts. The Blue Imperial pea is the
+    offspring of the Blue Prussian, and has larger seed and broader pods
+    than its parent. Now Mr. Masters, of Canterbury, a careful observer and
+    a raiser of new varieties of the pea, states[868] that the Blue
+    Imperial always has a strong tendency to revert to its parent-stock,
+    and the reversion "occurs in this manner: the last (or uppermost) pea
+    in the pod is frequently much smaller than the rest; and if these small
+    peas are carefully collected and sown separately, very many more, in
+    proportion, will revert to their origin, than those taken from the
+    other parts of the pod." Again M. Chate[869] says that in raising
+    seedling stocks he succeeds in getting eighty per cent. to bear double
+    flowers, by leaving only a few of the secondary branches to seed; but
+    in addition to this, "at the time of extracting the seeds, the upper
+    portion of the pod is separated and {348} placed aside, because it has
+    been ascertained that the plants coming from the seeds situated in this
+    portion of the pod, give eighty per cent. of single flowers." Now the
+    production of single-flowering plants from the seed of double-flowering
+    plants is clearly a case of reversion. These latter facts, as well as
+    the connection between a central position and pelorism and
+    prolification, show in an interesting manner how small a
+    difference--namely a little greater freedom in the flow of sap towards
+    one part of the same plant--determines important changes of structure.
+
+       *       *       *       *       *
+
+_Analogous or Parallel Variation._--By this term I wish to express that
+similar characters occasionally make their appearance in the several
+varieties or races descended from the same species, and more rarely in the
+offspring of widely distinct species. We are here concerned, not as
+hitherto with the causes of variation, but with the results; but this
+discussion could not have been more conveniently introduced elsewhere. The
+cases of analogous variation, as far as their origin is concerned, may be
+grouped, disregarding minor subdivisions, under two main heads; firstly,
+those due to unknown causes having acted on organic beings with nearly the
+same constitution, and which consequently vary in an analogous manner; and
+secondly, those due to the reappearance of characters which were possessed
+by a more or less remote progenitor. But these two main divisions can often
+be only conjecturally separated, and graduate, as we shall presently see,
+into each other.
+
+    Under the first head of analogous variations, not due to reversion, we
+    have the many cases of trees belonging to quite different orders which
+    have produced pendulous and fastigate varieties. The beech, hazel, and
+    barberry have given rise to purple-leaved varieties; and as Bernhardi
+    has remarked,[870] a multitude of plants, as distinct as possible, have
+    yielded varieties with deeply-cut or laciniated leaves. Varieties
+    descended from three distinct species of Brassica have their stems, or
+    so-called roots, enlarged into globular masses. The nectarine is the
+    offspring of the peach; and the varieties of both these trees offer a
+    remarkable parallelism in the fruit being white, red, or yellow
+    fleshed--in being clingstones or freestones--in the flowers being large
+    or small--in the leaves being serrated or crenated, furnished with
+    globose or reniform glands, or quite destitute of glands. It should be
+    remarked that each variety of the nectarine has not derived its
+    character from a corresponding variety of the peach. The several
+    varieties also of a closely allied genus, namely the apricot, differ
+    from each other in nearly the same parallel manner. There is no reason
+    {349} to believe that in any of these cases long-lost characters have
+    reappeared, and in most of them this certainly has not occurred.
+
+    Three species of Cucurbita have yielded a multitude of races, which
+    correspond so closely in character that, as Naudin insists, they may be
+    arranged in an almost strictly parallel series. Several varieties of
+    the melon are interesting from resembling in important characters other
+    species, either of the same genus or of allied genera; thus, one
+    variety has fruit so like, both externally and internally, the fruit of
+    a perfectly distinct species, namely, the cucumber, as hardly to be
+    distinguished from it; another has long cylindrical fruit twisting
+    about like a serpent; in another the seeds adhere to portions of the
+    pulp; in another the fruit, when ripe, suddenly cracks and falls into
+    pieces; and all these highly remarkable peculiarities are
+    characteristic of species belonging to allied genera. We can hardly
+    account for the appearance of so many unusual characters by reversion
+    to a single ancient form; but we must believe that all the members of
+    the family have inherited a nearly similar constitution from an early
+    progenitor. Our cereal and many other plants offer similar cases.
+
+    With animals we have fewer cases of analogous variation, independently
+    of direct reversion. We see something of the kind in the resemblance
+    between the short-muzzled races of the dog, such as the pug and
+    bulldog; in feather-footed races of the fowl, pigeon, and canary-bird;
+    in horses of the most different races presenting the same range of
+    colour; in all black-and-tan dogs having tan-coloured eye-spots and
+    feet, but in this latter case reversion may possibly have played a
+    part. Low has remarked[871] that several breeds of cattle are
+    "sheeted,"--that is, have a broad band of white passing round their
+    bodies like a sheet; this character is strongly inherited and sometimes
+    originates from a cross; it may be the first step in reversion to an
+    original or early type, for, as was shown in the third chapter, white
+    cattle with dark ears, feet, and tip of tail formerly existed, and now
+    exist in a feral or semi-feral condition in several quarters of the
+    world.
+
+    Under our second main division, namely, of analogous variations due to
+    reversion, the best cases are afforded by animals, and by none better
+    than by pigeons. In all the most distinct breeds sub-varieties
+    occasionally appear coloured exactly like the parent rock-pigeon, with
+    black wing-bars, white loins, banded tail, &c.; and no one can doubt
+    that these characters are simply due to reversion. So with minor
+    details; turbits properly have white tails, but occasionally a bird is
+    born with a dark-coloured and banded tail; pouters properly have white
+    primary wing-feathers, but not rarely a "sword-flighted" bird, that is,
+    one with the few first primaries dark-coloured, appears; and in these
+    cases we have characters proper to the rock-pigeon, but new to the
+    breed, evidently appearing from reversion. In some domestic varieties
+    the wing-bars, instead of being simply black, as in the rock-pigeon,
+    are beautifully edged with different zones of colour, and they then
+    present a striking analogy with the wing-bars in certain natural
+    species of the same family, such as _Phaps chalcoptera_; and this may
+    probably be accounted for by {350} all the forms descended from the
+    same remote progenitor having a tendency to vary in the same manner.
+    Thus also we can perhaps understand the fact of some Laugher-pigeons
+    cooing almost like turtle-doves, and of several races having
+    peculiarities in their flight, for certain natural species (viz. _C.
+    torquatrix_ and _palumbus_) display singular vagaries in this respect.
+    In other cases a race, instead of imitating in character a distinct
+    species, resembles some other race; thus certain runts tremble and
+    slightly elevate their tails, like fantails; and turbits inflate the
+    upper part of their oesophagus, like pouter-pigeons.
+
+    It is a common circumstance to find certain coloured marks persistently
+    characterising all the species of a genus, but differing much in tint;
+    and the same thing occurs with the varieties of the pigeon: thus,
+    instead of the general plumage being blue with the wing-bars black,
+    there are snow-white varieties with red bars, and black varieties with
+    white bars; in other varieties the wing-bars, as we have seen, are
+    elegantly zoned with different tints. The Spot pigeon is characterised
+    by the whole plumage being white, excepting the tail and a spot on the
+    forehead; but these parts may be red, yellow, or black. In the
+    rock-pigeon and in many varieties the tail is blue, with the outer
+    edges of the outer feathers white; but in one sub-variety of the
+    monk-pigeon we have a reversed variation, for the tail is white, except
+    the outer edges of the outer feathers, which are black.[872]
+
+    With some species of birds, for instance with gulls, certain coloured
+    parts appear as if almost washed out, and I have observed exactly the
+    same appearance in the terminal dark tail-bar in certain pigeons, and
+    in the whole plumage of certain varieties of the duck. Analogous facts
+    in the vegetable kingdom could be given.
+
+    Many sub-varieties of the pigeon have reversed and somewhat lengthened
+    feathers on the back part of their heads, and this is certainly not due
+    to reversion to the parent-species, which shows no trace of such
+    structure; but when we remember that sub-varieties of the fowl, turkey,
+    canary-bird, duck, and goose, all have topknots or reversed feathers on
+    their heads; and when we remember that scarcely a single large natural
+    group of birds can be named, in which some members have not a tuft of
+    feathers on their heads, we may suspect that reversion to some
+    extremely remote form has come into action.
+
+    Several breeds of the fowl have either spangled or pencilled feathers;
+    and these cannot be derived from the parent-species, the _Gallus
+    bankiva_; though of course it is possible that an early progenitor of
+    this species may have been spangled, and a still earlier or a later
+    progenitor may have been pencilled. But as many gallinaceous birds are
+    spangled or pencilled, it is a more probable view that the several
+    domestic breeds of the fowl have acquired this kind of plumage from all
+    the members of the family inheriting a tendency to vary in a like
+    manner. The same principle may account for the ewes in certain breeds
+    of sheep being hornless, like the females of some other hollow-horned
+    ruminants; it may account for certain domestic cats having
+    slightly-tufted ears, like those of the lynx; and for the skulls of
+    domestic rabbits often differing from each {351} other in the same
+    characters by which the skulls of the various species of the genus
+    Lepus differ.
+
+    I will only allude to one other case, already discussed. Now that we
+    know that the wild parent of the ass has striped legs, we may feel
+    confident that the occasional appearance of stripes on the legs of the
+    domestic ass is due to direct reversion; but this will not account for
+    the lower end of the shoulder-stripe being sometimes angularly bent or
+    slightly forked. So, again, when we see dun and other coloured horses
+    with stripes on the spine, shoulders, and legs, we are led, from
+    reasons formerly given, to believe that they reappear from direct
+    reversion to the wild parent-horse. But when horses have two or three
+    shoulder-stripes with one of them occasionally forked at the lower end,
+    or when they have stripes on their faces, or as foals are faintly
+    striped over nearly their whole bodies, with the stripes angularly bent
+    one under the other on the forehead, or irregularly branched in other
+    parts, it would be rash to attribute such diversified characters to the
+    reappearance of those proper to the aboriginal wild horse. As three
+    African species of the genus are much striped, and as we have seen that
+    the crossing of the unstriped species often leads to the hybrid
+    offspring being conspicuously striped--bearing also in mind that the
+    act of crossing certainly causes the reappearance of long-lost
+    characters--it is a more probable view that the above-specified stripes
+    are due to reversion, not to the immediate wild parent-horse, but to
+    the striped progenitor of the whole genus.
+
+I have discussed this subject of analogous variation at considerable
+length, because, in a future work on natural species, it will be shown that
+the varieties of one species frequently mock distinct species--a fact in
+perfect harmony with the foregoing cases, and explicable only on the theory
+of descent. Secondly, because these facts are important from showing, as
+remarked in a former chapter, that each trifling variation is governed by
+law, and is determined in a much higher degree by the nature of the
+organisation, than by the nature of the conditions to which the varying
+being has been exposed. Thirdly, because these facts are to a certain
+extent related to a more general law, namely, that which Mr. B. D.
+Walsh[873] has called the "Law of _Equable Variability_," or, as he
+explains it, "if any given character is very variable in one species of a
+group, it will tend to be variable in allied species; and if any given
+character is perfectly constant in one species of a group, it will tend to
+be constant in allied species."
+
+This leads me to recall a discussion in the chapter on Selection, in which
+it was shown that with domestic races, which are {352} now undergoing rapid
+improvement, those parts or characters which are the most valued vary the
+most. This naturally follows from recently selected characters continually
+tending to revert to their former less improved standard, and from their
+being still acted on by the same agencies, whatever these may be, which
+first caused the characters in question to vary. The same principle is
+applicable to natural species, for, as stated in my 'Origin of Species,'
+generic characters are less variable than specific characters; and the
+latter are those which have been modified by variation and natural
+selection, since the period when all the species belonging to the same
+genus branched off from a common progenitor, whilst generic characters are
+those which have remained unaltered from a much more remote epoch, and
+accordingly are now less variable. This statement makes a near approach to
+Mr. Walsh's law of Equable Variability. Secondary sexual characters, it may
+be added, rarely serve to characterise distinct genera, for they usually
+differ much in the species of the same genus, and are highly variable in
+the individuals of the same species; we have also seen in the earlier
+chapters of this work how variable secondary sexual characters become under
+domestication.
+
+_Summary of the three previous Chapters, on the Laws of Variation._
+
+In the twenty-third chapter we have seen that changed conditions
+occasionally act in a definite manner on the organisation, so that all, or
+nearly all, the individuals thus exposed become modified in the same
+manner. But a far more frequent result of changed conditions, whether
+acting directly on the organisation or indirectly through the reproductive
+system being affected is indefinite and fluctuating variability. In the
+three latter chapters we have endeavoured to trace some of the laws by
+which such variability is regulated.
+
+Increased use adds the size of a muscle, together with the blood-vessels,
+nerves, ligaments, the crests of bone to which these are attached, the
+whole bone and other connected bones. So it is with various glands.
+Increased functional activity strengthens the sense-organs. Increased and
+intermittent pressure thickens the epidermis; and a change in the nature of
+the food sometimes modifies the coats of the stomach, and increases or
+{353} decreases the length of the intestines. Continued disuse, on the
+other hand, weakens and diminishes all parts of the organisation. Animals
+which during many generations have taken but little exercise, have their
+lungs reduced in size, and as a consequence the bony fabric of the chest,
+and the whole form of the body, become modified. With our anciently
+domesticated birds, the wings have been little used, and they are slightly
+reduced; with their decrease, the crest of the sternum, the scapulae,
+coracoids, and furcula, have all been reduced.
+
+With domesticated animals, the reduction of a part from disuse is never
+carried so far that a mere rudiment is left, but we have good reason to
+believe that this has often occurred under nature. The cause of this
+difference probably is that with domestic animals not only sufficient time
+has not been granted for so profound a change, but that, from not being
+exposed to a severe struggle for life, the principle of the economy of
+organisation does not come into action. On the contrary, we sometimes see
+that structures which are rudimentary in the parent-species become
+partially redeveloped in their domesticated progeny. When rudiments are
+formed or left under domestication, they are the result of a sudden arrest
+of development, and not of long-continued disuse with the absorption of all
+superfluous parts; nevertheless they are of interest, as showing that
+rudiments are the relics of organs once perfectly developed.
+
+Corporeal, periodical, and mental habits, though the latter have been
+almost passed over in this work, become changed under domestication, and
+the changes are often inherited. Such changed habits in any organic being,
+especially when living a free life, would often lead to the augmented or
+diminished use of various organs, and consequently to their modification.
+From long-continued habit, and more especially from the occasional birth of
+individuals with a slightly different constitution, domestic animals and
+cultivated plants become to a certain extent acclimatised, or adapted to a
+climate different from that proper to the parent-species.
+
+Through the principle of correlated variability, when one part varies other
+parts vary,--either simultaneously, or one after the other. Thus an organ
+modified during an early embryonic period affects other parts subsequently
+developed. When an {354} organ, such as the beak, increases or decreases in
+length, adjoining or correlated parts, as the tongue and the orifice of the
+nostrils, tend to vary in the same manner. When the whole body increases or
+decreases in size, various parts become modified; thus with pigeons the
+ribs increase or decrease in number and breadth. Homologous parts, which
+are identical during their early development and are exposed to similar
+conditions, tend to vary in the same or in some connected manner,--as in
+the case of the right and left sides of the body, of the front and hind
+limbs, and even of the head and limbs. So it is with the organs of sight
+and hearing; for instance, white cats with blue eyes are almost always
+deaf. There is a manifest relation throughout the body between the skin and
+its various appendages of hair, feathers, hoofs, horns, and teeth. In
+Paraguay, horses with curly hair have hoofs like those of a mule; the wool
+and the horns of sheep vary together; hairless dogs are deficient in their
+teeth; men with redundant hair have abnormal teeth, either deficient or in
+excess. Birds with long wing-feathers usually have long tail-feathers. When
+long feathers grow from the outside of the legs and toes of pigeons, the
+two outer toes are connected by membrane; for the whole leg tends to assume
+the structure of the wing. There is a manifest relation between a crest of
+feathers on the head and a marvellous amount of change in the skull of
+various fowls; and in a lesser degree, between the greatly elongated,
+lopping ears of rabbits and the structure of their skulls. With plants, the
+leaves, various parts of the flower, and the fruit, often vary together in
+a correlated manner.
+
+In some cases we find correlation without being able even to conjecture
+what is the nature of the connexion, as with various correlated
+monstrosities and diseases. This is likewise the case with the colour of
+the adult pigeon, in connexion with the presence of down on the young bird.
+Numerous curious instances have been given of peculiarities of
+constitution, in correlation with colour, as shown by the immunity of
+individuals of some one colour from certain diseases, from the attacks of
+parasites, and from the action of certain vegetable poisons.
+
+Correlation is an important subject; for with species, and in a lesser
+degree with domestic races, we continually find that {355} certain parts
+have been greatly modified to serve some useful purpose; but we almost
+invariably find that other parts have likewise been more or less modified,
+without our being able to discover any advantage in the change. No doubt
+great caution is necessary in coming to this conclusion, for it is
+difficult to overrate our ignorance on the use of various parts of the
+organisation; but from what we have now seen, we may believe that many
+modifications are of no direct service, having arisen in correlation with
+other and useful changes.
+
+Homologous parts during their early development evince an affinity for each
+other,--that is, they tend to cohere and fuse together much more readily
+than other parts. This tendency to fusion explains a multitude of normal
+structures. Multiple and homologous organs are especially liable to vary in
+number and probably in form. As the supply of organised matter is not
+unlimited, the principle of compensation sometimes comes into action; so
+that, when one part is greatly developed, adjoining parts or functions are
+apt to be reduced; but this principle is probably of much less importance
+than the more general one of the economy of growth. Through mere mechanical
+pressure hard parts occasionally affect soft adjoining parts. With plants
+the position of the flowers on the axis, and of the seeds in the capsule,
+sometimes leads, through a freer flow of sap, to changes of structure; but
+these changes are often due to reversion. Modifications, in whatever manner
+caused, will be to a certain extent regulated by that co-ordinating power
+or _nisus formativus_, which is in fact a remnant of one of the forms of
+reproduction, displayed by many lowly organised beings in their power of
+fissiparous generation and budding. Finally, the effects of the laws, which
+directly or indirectly govern variability, may be largely influenced by
+man's selection, and will so far be determined by natural selection that
+changes advantageous to any race will be favoured and disadvantageous
+changes checked.
+
+Domestic races descended from the same species, or from two or more allied
+species, are liable to revert to characters derived from their common
+progenitor, and, as they have much in common in their constitutions, they
+are also liable under changed conditions to vary in the same manner; from
+these {356} two causes analogous varieties often arise. When we reflect on
+the several foregoing laws, imperfectly as we understand them, and when we
+bear in mind how much remains to be discovered, we need not be surprised at
+the extremely intricate manner in which our domestic productions have
+varied, and still go on varying.
+
+       *       *       *       *       *
+
+
+{357}
+
+CHAPTER XXVII.
+
+PROVISIONAL HYPOTHESIS OF PANGENESIS.
+
+    PRELIMINARY REMARKS.--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A
+    SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE
+    DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE
+    FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE
+    BODY--VARIABILITY--INHERITANCE--REVERSION.
+
+    SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY
+    ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE
+    SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.
+
+In the previous chapters large classes of facts, such as those bearing on
+bud-variation, the various forms of inheritance, the causes and laws of
+variation, have been discussed; and it is obvious that these subjects, as
+well as the several modes of reproduction, stand in some sort of relation
+to each other. I have been led, or rather forced, to form a view which to a
+certain extent connects these facts by a tangible method. Every one would
+wish to explain to himself, even in an imperfect manner, how it is possible
+for a character possessed by some remote ancestor suddenly to reappear in
+the offspring; how the effects of increased or decreased use of a limb can
+be transmitted to the child; how the male sexual element can act not solely
+on the ovule, but occasionally on the mother-form; how a limb can be
+reproduced on the exact line of amputation, with neither too much nor too
+little added; how the various modes of reproduction are connected, and so
+forth. I am aware that my view is merely a provisional hypothesis or
+speculation; but until a better one be advanced, it may be serviceable by
+bringing together a multitude of facts which are at present left
+disconnected by any efficient cause. As Whewell, the historian of the
+inductive sciences, remarks:--"Hypotheses may often be of service to
+science, when they involve a certain portion of incompleteness, and even of
+error." Under this point of view I venture to advance the hypothesis of
+Pangenesis, which {358} implies that the whole organisation, in the sense
+of every separate atom or unit, reproduces itself. Hence ovules and
+pollen-grains,--the fertilised seed or egg, as well as buds,--include and
+consist of a multitude of germs thrown off from each separate atom of the
+organism.
+
+In the First Part I will enumerate as briefly as I can the groups of facts
+which seem to demand connection; but certain subjects, not hitherto
+discussed, must be treated at disproportionate length. In the Second Part
+the hypothesis will be given; and we shall see, after considering how far
+the necessary assumptions are in themselves improbable, whether it serves
+to bring under a single point of view the various facts.
+
+PART I.
+
+Reproduction may be divided into two main classes, namely, sexual and
+asexual. The latter is effected in many ways--by gemmation, that is by the
+formation of buds of various kinds, and by fissiparous generation, that is
+by spontaneous or artificial division. It is notorious that some of the
+lower animals, when cut into many pieces, reproduce so many perfect
+individuals: Lyonnet cut a Nais or freshwater worm into nearly forty
+pieces, and these all reproduced perfect animals.[874] It is probable that
+segmentation could be carried much further in some of the protozoa, and
+with some of the lowest plants each cell will reproduce the parent-form.
+Johannes Mueller thought that there was an important distinction between
+gemmation and fission; for in the latter case the divided portion, however
+small, is more perfectly organised; but most physiologists are now
+convinced that the two processes are essentially alike.[875] Prof. Huxley
+remarks, "fission is little more than a peculiar {359} mode of budding,"
+and Prof. H. J. Clark, who has especially attended to this subject, shows
+in detail that there is sometimes "a compromise between self-division and
+budding." When a limb is amputated, or when the whole body is bisected, the
+cut extremities are said to bud forth; and as the papilla, which is first
+formed, consists of undeveloped cellular tissue like that forming an
+ordinary bud, the expression is apparently correct. We see the connection
+of the two processes in another way; for Trembley observed that with the
+hydra the reproduction of the head after amputation was checked as soon as
+the animal began to bud.[876]
+
+Between the production, by fissiparous generation, of two or more complete
+individuals, and the repair of even a very slight injury, we have, as
+remarked in a former chapter, so perfect and insensible a gradation, that
+it is impossible to doubt that they are connected processes. Between the
+power which repairs a trifling injury in any part, and the power which
+previously "was occupied in its maintenance by the continued mutation of
+its particles," there cannot be any great difference; and we may follow Mr.
+Paget in believing them to be the selfsame power. As at each stage of
+growth an amputated part is replaced by one in the same state of
+development, we must likewise follow Mr. Paget in admitting "that the
+powers of development from the embryo are identical with those exercised
+for the restoration from injuries: in other words, that the powers are the
+same by which perfection is first achieved, and by which, when lost, it is
+recovered."[877] Finally, we may conclude that the several forms of
+gemmation, and of fissiparous generation, the repair of injuries, the
+maintenance of each part in its proper state, and the growth or progressive
+development of the whole structure of the embryo, are all essentially the
+results of one and the same great power.
+
+_Sexual Generation._--The union of the two sexual elements seems to make a
+broad distinction between sexual and asexual reproduction. But the
+well-ascertained cases of Parthenogenesis prove that the distinction is not
+really so great as it at first appears; for ovules occasionally, and even
+in some cases {360} frequently, become developed into perfect beings,
+without the concourse of the male element. J. Mueller and others admit that
+ovules and buds have the same essential nature. Certain bodies, which
+during their early development cannot be distinguished by any external
+character from true ovules, nevertheless must be classed as buds, for
+though formed within the ovarium they are incapable of fertilisation. This
+is the case with the germ-balls of the Cecidomyide larvae, as described by
+Leuckart.[878] Ovules and the male element, before they become united,
+have, like buds, an independent existence.[879] Both have the power of
+transmitting every single character possessed by the parent-form. We see
+this clearly when hybrids are paired _inter se_, for the characters of
+either grandparent often reappear, either perfectly or by segments, in the
+progeny. It is an error to suppose that the male transmits certain
+characters and the female other characters; though no doubt, from unknown
+causes, one sex sometimes has a stronger power of transmission than the
+other.
+
+It has been maintained by some authors that a bud differs essentially from
+a fertilised germ, by always reproducing the perfect character of the
+parent-stock; whilst fertilised germs become developed into beings which
+differ, in a greater or less degree, from each other and from their
+parents. But there is no such broad distinction as this. In the eleventh
+chapter, numerous cases were given showing that buds occasionally grow into
+plants having new and strongly marked characters; and varieties thus
+produced can be propagated for a length of time by buds, and occasionally
+by seed. Nevertheless, it must be admitted that beings produced sexually
+are much more liable to vary than those produced asexually; and of this
+fact a partial explanation will hereafter be attempted. The variability in
+both cases is determined by the same general causes, and is governed by the
+same laws. Hence new varieties arising from buds cannot be distinguished
+from those arising from seed. Although bud-varieties usually retain their
+character during {361} successive bud-generations, yet they occasionally
+revert, even after a long series of bud-generations, to their former
+character. This tendency to reversion in buds is one of the most remarkable
+of the several points of agreement between the offspring from bud and
+seminal reproduction.
+
+There is, however, one difference between beings produced sexually and
+asexually, which is very general. The former usually pass in the course of
+their development from a lower to a higher grade, as we see in the
+metamorphoses of insects and in the concealed metamorphoses of the
+vertebrata; but this passage from a lower to a higher grade cannot be
+considered as a necessary accompaniment of sexual reproduction, for hardly
+anything of the kind occurs in the development of Aphis amongst insects, or
+with certain crustaceans, cephalopods, or with any of the higher vascular
+plants. Animals propagated asexually by buds or fission are on the other
+hand never known to undergo a retrogressive metamorphosis; that is, they do
+not first sink to a lower, before passing on to their higher and final
+stage of development. But during the act of asexual production or
+subsequently to it, they often advance in organisation, as we see in the
+many cases of "alternate generation." In thus speaking of alternate
+generation, I follow those naturalists who look at the process as
+essentially one of internal budding or of fissiparous generation. Some of
+the lower plants, however, such as mosses and certain algae, according to
+Dr. L. Radlkofer,[880] when propagated asexually, do undergo a
+retrogressive metamorphosis. We can to a certain extent understand, as far
+as the final cause is concerned, why beings propagated by buds should so
+rarely retrogress during development; for with each organism the structure
+acquired at each stage of development must be adapted to its peculiar
+habits. Now, with beings produced by gemmation,--and this, differently from
+sexual reproduction, may occur at any period of growth,--if there were
+places for the support of many individuals at some one stage of
+development, the simplest plan would be that they should be multiplied by
+gemmation at that stage, and not that they should first retrograde in their
+development to an earlier or simpler structure, which might not be fitted
+for the surrounding conditions.
+
+{362}
+
+From the several foregoing considerations we may conclude that the
+difference between sexual and asexual generation is not nearly so great as
+it at first appears; and we have already seen that there is the closest
+agreement between gemmation, fissiparous generation, the repair of
+injuries, and ordinary growth or development. The capacity of fertilisation
+by the male element seems to be the chief distinction between an ovule and
+a bud; and this capacity is not invariably brought into action, as in the
+cases of parthenogenetic reproduction. We are here naturally led to inquire
+what the final cause can be of the necessity in ordinary generation for the
+concourse of the two sexual elements.
+
+Seeds and ova are often highly serviceable as the means of disseminating
+plants and animals, and of preserving them during one or more seasons in a
+dormant state; but unimpregnated seeds or ova, and detached buds, would be
+equally serviceable for both purposes. We can, however, indicate two
+important advantages gained by the concourse of the two sexes, or rather of
+two individuals belonging to opposite sexes; for, as I have shown in a
+former chapter, the structure of every organism appears to be especially
+adapted for the concurrence, at least occasionally, of two individuals. In
+nearly the same manner as it is admitted by naturalists that hybridism,
+from inducing sterility, is of service in keeping the forms of life
+distinct and fitted for their proper places; so, when species are rendered
+highly variable by changed conditions of life, the free intercrossing of
+the varying individuals will tend to keep each form fitted for its proper
+place in nature; and crossing can be effected only by sexual generation,
+but whether the end thus gained is of sufficient importance to account for
+the first origin of sexual intercourse is very doubtful. Secondly, I have
+shown, from the consideration of a large body of facts, that, as a slight
+change in the conditions of life is beneficial to each creature, so, in an
+analogous manner, is the change effected in the germ by sexual union with a
+distinct individual; and I have been led, from observing the many
+widely-extended provisions throughout nature for this purpose, and from the
+greater vigour of crossed organisms of all kinds, as proved by direct
+experiments, as well as from the evil effects of close interbreeding when
+long {363} continued, to believe that the advantage thus gained is very
+great. Besides these two important ends, there may, of course, be others,
+as yet unknown to us, gained by the concourse of the two sexes.
+
+Why the germ, which before impregnation undergoes a certain amount of
+development, ceases to progress and perishes, unless it be acted on by the
+male element; and why conversely the male element, which is enabled to keep
+alive for even four or five years within the spermatheca of a female
+insect, likewise perishes, unless it acts on or unites with the germ, are
+questions which cannot be answered with any certainty. It is, however,
+possible that both sexual elements perish, unless brought into union,
+simply from including too little formative matter for independent existence
+and development; for certainly they do not in ordinary cases differ in
+their power of giving character to the embryo. This view of the importance
+of the quantity of formative matter seems probable from the following
+considerations. There is no reason to suspect that the spermatozoa or
+pollen-grains of the same individual animal or plant differ from each
+other; yet Quatrefages has shown in the case of the Teredo,[881] as did
+formerly Prevost and Dumas with other animals, that more than one
+spermatozoon is requisite to fertilise an ovule. This has likewise been
+clearly proved by Newport,[882] who adds the important fact, established by
+numerous experiments, that, when a very small number of spermatozoa are
+applied to the ova of Batrachians, they are only partially impregnated and
+the embryo is never fully developed: the first step, however, towards
+development, namely, the partial segmentation of the yelk, does occur to a
+greater or less extent, but is never completed up to granulation. The rate
+of the segmentation is likewise determined by the number of the
+spermatozoa. With respect to plants, nearly the same results were obtained
+by Koelreuter and Gaertner. This last careful observer found,[883] after
+making successive trials on a Malva with more and more pollen-grains, that
+even thirty grains did not fertilise a single seed; but when forty grains
+were applied to the {364} stigma, a few seeds of small size were formed.
+The pollen-grains of Mirabilis are extraordinarily large, and the ovarium
+contains only a single ovule; and these circumstances led Naudin[884] to
+make the following interesting experiments: a flower was fertilised by
+three grains and succeeded perfectly; twelve flowers were fertilised by two
+grains, and seventeen flowers by a single grain, and of these one flower
+alone in each lot perfected its seed; and it deserves especial notice that
+the plants produced by these two seeds never attained their proper
+dimensions, and bore flowers of remarkably small size. From these facts we
+clearly see that the quantity of the peculiar formative matter which is
+contained within the spermatozoa and pollen-grains is an all-important
+element in the act of fertilisation, not only in the full development of
+the seed, but in the vigour of the plant produced from such seed. We see
+something of the same kind in certain cases of parthenogenesis, that is,
+when the male element is wholly excluded; for M. Jourdan[885] found that,
+out of about 58,000 eggs laid by unimpregnated silk-moths, many passed
+through their early embryonic stages, showing that they were capable of
+self-development, but only twenty-nine out of the whole number produced
+caterpillars. Therefore it is not an improbable view that deficient bulk or
+quantity in the formative matter, contained within the sexual elements, is
+the main cause of their not having the capacity of prolonged separate
+existence and development. The belief that it is the function of the
+spermatozoa to communicate life to the ovule seems a strange one, seeing
+that the unimpregnated ovule is already alive and continues for a
+considerable time alive. We shall hereafter see that it is probable that
+the sexual elements, or possibly only the female element, include certain
+primordial cells, that is, such as have undergone no differentiation, and
+which are not present in an active state in buds.
+
+_Graft-hybrids._--When discussing in the eleventh chapter the curious case
+of the _Cytisus adami_, facts were given which render it to a certain
+degree probable, in accordance with the belief of some distinguished
+botanists, that, when the tissues of two plants {365} belonging to distinct
+species or varieties are intimately united, buds are afterwards
+occasionally produced which, like hybrids, combine the characters of the
+two united forms. It is certain that when trees with variegated leaves are
+grafted or budded on a common stock, the latter sometimes produces buds
+bearing variegated leaves; but this may perhaps be looked at as a case of
+inoculated disease. Should it ever be proved that hybridised buds can be
+formed by the union of two distinct vegetative tissues, the essential
+identity of sexual and asexual reproduction would be shown in the most
+interesting manner; for the power of combining in the offspring the
+characters of both parents, is the most striking of all the functions of
+sexual generation.
+
+_Direct Action of the Male Element on the Female._--In the chapter just
+referred to, I have given abundant proofs that foreign pollen occasionally
+affects the mother-plant in a direct manner. Thus, when Gallesio fertilised
+an orange-flower with pollen from the lemon, the fruit bore stripes of
+perfectly characterised lemon-peel: with peas, several observers have seen
+the colour of the seed-coats and even of the pod directly affected by the
+pollen of a distinct variety; so it has been with the fruit of the apple,
+which consists of the modified calyx and upper part of the flower-stalk.
+These parts in ordinary cases are wholly formed by the mother-plant. We
+here see the male element affecting and hybridising not that part which it
+is properly adapted to affect, namely the ovule, but the partially
+developed tissues of a distinct individual. We are thus brought half-way
+towards a graft-hybrid, in which the cellular tissue of one form, instead
+of its pollen, is believed to hybridise the tissues of a distinct form. I
+formerly assigned reasons for rejecting the belief that the mother-plant is
+affected through the intervention of the hybridised embryo; but even if
+this view were admitted, the case would become one of graft-hybridism, for
+the fertilised embryo and the mother-plant must be looked at as distinct
+individuals.
+
+With animals which do not breed until nearly mature, and of which all the
+parts are then fully developed, it is hardly possible that the male element
+should directly affect the female. But we have the analogous and perfectly
+well-ascertained case of the male element of a distinct form, as with the
+{366} quagga and Lord Morton's mare, affecting the ovarium of the female,
+so that the ovules and offspring subsequently produced by her when
+impregnated by other males are plainly affected and hybridised by the first
+male.
+
+_Development._--The fertilised germ reaches maturity by a vast number of
+changes: these are either slight and slowly effected, as when the child
+grows into the man, or are great and sudden, as with the metamorphoses of
+most insects. Between these extremes we have, even within the same class,
+every gradation: thus, as Sir J. Lubbock has shown,[886] there is an
+Ephemerous insect which moults above twenty times, undergoing each time a
+slight but decided change of structure; and these changes, as he further
+remarks, probably reveal to us the normal stages of development which are
+concealed and hurried through, or suppressed, in most other insects. In
+ordinary metamorphoses, the parts and organs appear to become changed into
+the corresponding parts in the next stage of development; but there is
+another form of development, which has been called by Professor Owen
+metagenesis. In this case "the new parts are not moulded upon the inner
+surface of the old ones. The plastic force has changed its course of
+operation. The outer case, and all that gave form and character to the
+precedent individual, perish and are cast off; they are not changed into
+the corresponding parts of the new individual. These are due to a new and
+distinct developmental process," &c.[887] Metamorphosis, however, graduates
+so insensibly into metagenesis, that the two processes cannot be distinctly
+separated. For instance, in the last change which Cirripedes undergo, the
+alimentary canal and some other organs are moulded on pre-existing parts;
+but the eyes of the old and the young animal are developed in entirely
+different parts of the body; the tips of the mature limbs are formed within
+the larval limbs, and may be said to be metamorphosed from them; but their
+basal portions and the whole thorax are developed in a plane actually at
+right angles to the limbs and thorax of the larva; and this {367} may be
+called metagenesis. The metagenetic process is carried to an extreme degree
+in the development of some Echinoderms, for the animal in the second stage
+of development is formed almost like a bud within the animal of the first
+stage, the latter being then cast off like an old vestment, yet sometimes
+still maintaining for a short period an independent vitality.[888]
+
+If, instead of a single individual, several were to be thus developed
+metagenetically within a pre-existing form, the process would be called one
+of alternate generation. The young thus developed may either closely
+resemble the encasing parent-form, as with the larvae of Cecidomyia, or may
+differ to an astonishing degree, as with many parasitic worms and with
+jelly-fishes; but this does not make any essential difference in the
+process, any more than the greatness or abruptness of the change in the
+metamorphoses of insects.
+
+The whole question of development is of great importance for our present
+subject. When an organ, the eye for instance, is metagenetically formed in
+a part of the body where during the previous stage of development no eye
+existed, we must look at it as a new and independent growth. The absolute
+independence of new and old structures, which correspond in structure and
+function, is still more obvious when several individuals are formed within
+a previous encasing form, as in the cases of alternate generation. The same
+important principle probably comes largely into play even in the case of
+continuous growth, as we shall see when we consider the inheritance of
+modifications at corresponding ages.
+
+We are led to the same conclusion, namely, the independence of parts
+successively developed, by another and quite distinct group of facts. It is
+well known that many animals belonging to the same class, and therefore not
+differing widely from each other, pass through an extremely different
+course of development. Thus certain beetles, not in any way remarkably
+different from others of the same order, undergo what has been called a
+hyper-metamorphosis--that is, they pass through an early stage wholly
+different from the ordinary grub-like larva. In the same sub-order of
+crabs, namely, the Macroura, as Fritz {368} Mueller remarks, the river
+cray-fish is hatched under the same form which it ever afterwards retains;
+the young lobster has divided legs, like a Mysis; the Palaemon appears
+under the form of a Zoea, and Peneus under the Nauplius-form; and how
+wonderfully these larval forms differ from each other, is known to every
+naturalist.[889] Some other crustaceans, as the same author observes, start
+from the same point and arrive at nearly the same end, but in the middle of
+their development are widely different from each other. Still more striking
+cases could be given with respect to the Echinodermata. With the Medusae or
+jelly-fishes Professor Allman observes, "the classification of the Hydroida
+would be a comparatively simple task if, as has been erroneously asserted,
+generically-identical medusoids always arose from generically-identical
+polypoids; and on the other hand, that generically-identical polypoids
+always gave origin to generically-identical medusoids." So, again, Dr.
+Strethill Wright remarks, "in the life-history of the Hydroidae any phase,
+planuloid, polypoid, or medusoid, may be absent."[890]
+
+According to the belief now generally accepted by our best naturalists, all
+the members of the same order or class, the Macrourous crustaceans for
+instance, are descended from a common progenitor. During their descent they
+have diverged much in structure, but have retained much in common; and this
+divergence and retention of character has been effected, though they have
+passed and still pass through marvellously different metamorphoses. This
+fact well illustrates how independent each structure must be from that
+which precedes and follows it in the course of development.
+
+_The Functional Independence of the Elements or Units of the
+Body._--Physiologists agree that the whole organism consists of a multitude
+of elemental parts, which are to a great extent independent of each other.
+Each organ, says Claude Bernard,[891] {369} has its proper life, its
+autonomy; it can develop and reproduce itself independently of the
+adjoining tissues. The great German authority, Virchow,[892] asserts still
+more emphatically that each system, as the nervous or osseous system, or
+the blood, consists of an "enormous mass of minute centres of action....
+Every element has its own special action, and even though it derive its
+stimulus to activity from other parts, yet alone effects the actual
+performance of its duties.... Every single epithelial and muscular
+fibre-cell leads a sort of parasitical existence in relation to the rest of
+the body.... Every single bone-corpuscle really possesses conditions of
+nutrition peculiar to itself." Each element, as Mr. Paget remarks, lives
+its appointed time, and then dies, and, after being cast off or absorbed,
+is replaced.[893] I presume that no physiologist doubts that, for instance,
+each bone-corpuscle of the finger differs from the corresponding corpuscle
+in the corresponding joint of the toe; and there can hardly be a doubt that
+even those on the corresponding sides of the body differ, though almost
+identical in nature. This near approach to identity is curiously shown in
+many diseases in which the same exact points on the right and left sides of
+the body are similarly affected; thus Mr. Paget[894] gives a drawing of a
+diseased pelvis, in which the bone has grown into a most complicated
+pattern, but "there is not one spot or line on one side which is not
+represented, as exactly as it would be in a mirror, on the other."
+
+Many facts support this view of the independent life of each minute element
+of the body. Virchow insists that a single bone-corpuscle or a single cell
+in the skin may become diseased. The spur of a cock, after being inserted
+into the eye of an ox, lived for eight years, and acquired a weight of 306
+grammes, or nearly fourteen ounces.[895] The tail of a pig has been grafted
+into the middle of its back, and reacquired sensibility. Dr. Ollier[896]
+inserted a piece of periosteum from the bone of a young dog under the skin
+of a rabbit, and true bone was developed. A multitude of similar facts
+could be given. The {370} frequent presence of hairs and of perfectly
+developed teeth, even teeth of the second dentition, in ovarian
+tumours,[897] are facts leading to the same conclusion.
+
+Whether each of the innumerable autonomous elements of the body is a cell
+or the modified product of a cell, is a more doubtful question, even if so
+wide a definition be given to the term, as to include cell-like bodies
+without walls and without nuclei.[898] Professor Lionel Beale uses the term
+"germinal matter" for the contents of cells, taken in this wide
+acceptation, and he draws a broad distinction between germinal matter and
+"formed material" or the various products of cells.[899] But the doctrine
+of _omnis cellula e cellula_ is admitted for plants, and is a widely
+prevalent belief with respect to animals.[900] Thus Virchow, the great
+supporter of the cellular theory, whilst allowing that difficulties exist,
+maintains that every atom of tissue is derived from cells, and these from
+pre-existing cells, and these primarily from the egg, which he regards as a
+great cell. That cells, still retaining the same nature, increase by
+self-division or proliferation, is admitted by almost every one. But when
+an organism undergoes a great change of structure during development, the
+cells, which at each stage are supposed to be directly derived from
+previously-existing cells, must likewise be greatly changed in nature; this
+change is apparently attributed by the supporters of the cellular doctrine
+to some inherent power which the cells possess, and not to any external
+agency.
+
+Another school maintains that cells and tissues of all kinds may be formed,
+independently of pre-existing cells, from plastic lymph or blastema; and
+this it is thought is well exhibited in the repair of wounds. As I have not
+especially attended to histology, it would be presumptuous in me to express
+an opinion on the two opposed doctrines. But every one appears to admit
+that the body consists of a multitude of "organic units,"[901] {371} each
+of which possesses its own proper attributes, and is to a certain extent
+independent of all others. Hence it will be convenient to use indifferently
+the terms cells or organic units or simply units.
+
+_Variability and Inheritance._--We have seen in the twenty-second chapter
+that variability is not a principle co-ordinate with life or reproduction,
+but results from special causes, generally from changed conditions acting
+during successive generations. Part of the fluctuating variability thus
+induced is apparently due to the sexual system being easily affected by
+changed conditions, so that it is often rendered impotent; and when not so
+seriously affected, it often fails in its proper function of transmitting
+truly the characters of the parents to the offspring. But variability is
+not necessarily connected with the sexual system, as we see from the cases
+of bud-variation; and although we may not be able to trace the nature of
+the connexion, it is probable that many deviations of structure which
+appear in sexual offspring result from changed conditions acting directly
+on the organisation, independently of the reproductive organs. In some
+instances we may feel sure of this, when all, or nearly all the individuals
+which have been similarly exposed are similarly and definitely affected--as
+in the dwarfed and otherwise changed maize brought from hot countries when
+cultivated in Germany; in the change of the fleece in sheep within the
+tropics; to a certain extent in the increased size and early maturity of
+our highly-improved domesticated animals; in inherited gout from
+intemperance; and in many other such cases. Now, as such changed conditions
+do not especially affect the reproductive organs, it seems mysterious on
+any ordinary view why their product, the new organic being, should be
+similarly affected.
+
+How, again, can we explain to ourselves the inherited effects of the use or
+disuse of particular organs? The domesticated duck flies less and walks
+more than the wild duck, and its limb-bones have become in a corresponding
+manner diminished and increased in comparison with those of the wild duck.
+A horse is trained to certain paces, and the colt inherits similar
+consensual movements. The domesticated rabbit becomes tame from close
+confinement; the dog intelligent from associating with man; the retriever
+is taught to fetch and carry: and these {372} mental endowments and bodily
+powers are all inherited. Nothing in the whole circuit of physiology is
+more wonderful. How can the use or disuse of a particular limb or of the
+brain affect a small aggregate of reproductive cells, seated in a distant
+part of the body, in such a manner that the being developed from these
+cells inherits the characters of either one or both parents? Even an
+imperfect answer to this question would be satisfactory.
+
+Sexual reproduction does not essentially differ, as we have seen, from
+budding or self-division, and these processes graduate through the repair
+of injuries into ordinary development and growth; it might therefore be
+expected that every character would be as regularly transmitted by all the
+methods of reproduction as by continued growth. In the chapters devoted to
+inheritance it was shown that a multitude of newly-acquired characters,
+whether injurious or beneficial, whether of the lowest or highest vital
+importance, are often faithfully transmitted--frequently even when one
+parent alone possesses some new peculiarity. It deserves especial attention
+that characters appearing at any age tend to reappear at a corresponding
+age. We may on the whole conclude that in all cases inheritance is the
+rule, and non-inheritance the anomaly. In some instances a character is not
+inherited, from the conditions of life being directly opposed to its
+development; in many instances, from the conditions incessantly inducing
+fresh variability, as with grafted fruit-trees and highly cultivated
+flowers. In the remaining cases the failure may be attributed to reversion,
+by which the child resembles its grandparents or more remote progenitors,
+instead of its parents.
+
+This principle of Reversion is the most wonderful of all the attributes of
+Inheritance. It proves to us that the transmission of a character and its
+development, which ordinarily go together and thus escape discrimination,
+are distinct powers; and these powers in some cases are even antagonistic,
+for each acts alternately in successive generations. Reversion is not a
+rare event, depending on some unusual or favourable combination of
+circumstances, but occurs so regularly with crossed animals and plants, and
+so frequently with uncrossed breeds, that it is evidently an essential part
+of the principle of inheritance. We know that {373} changed conditions have
+the power of evoking long-lost characters, as in the case of some feral
+animals. The act of crossing in itself possesses this power in a high
+degree. What can be more wonderful than that characters, which have
+disappeared during scores, or hundreds, or even thousands of generations,
+should suddenly reappear perfectly developed, as in the case of pigeons and
+fowls when purely bred, and especially when crossed; or as with the zebrine
+stripes on dun-coloured horses, and other such cases? Many monstrosities
+come under this same head, as when rudimentary organs are redeveloped, or
+when an organ which we must believe was possessed by an early progenitor,
+but of which not even a rudiment is left, suddenly reappears, as with the
+fifth stamen in some Scrophulariaceae. We have already seen that reversion
+acts in bud-reproduction; and we know that it occasionally acts during the
+growth of the same individual animal, especially, but not exclusively, when
+of crossed parentage,--as in the rare cases described of individual fowls,
+pigeons, cattle, and rabbits, which have reverted as they advanced in years
+to the colours of one of their parents or ancestors.
+
+We are led to believe, as formerly explained, that every character which
+occasionally reappears is present in a latent form in each generation, in
+nearly the same manner as in male and female animals secondary characters
+of the opposite sex lie latent, ready to be evolved when the reproductive
+organs are injured. This comparison of the secondary sexual characters
+which are latent in both sexes, with other latent characters, is the more
+appropriate from the case recorded of the Hen, which assumed some of the
+masculine characters, not of her own race, but of an early progenitor; she
+thus exhibited at the same time the redevelopment of latent characters of
+both kinds and connected both classes. In every living creature we may feel
+assured that a host of lost characters lie ready to be evolved under proper
+conditions. How can we make intelligible, and connect with other facts,
+this wonderful and common capacity of reversion,--this power of calling
+back to life long-lost characters? {374}
+
+PART II.
+
+I have now enumerated the chief facts which every one would desire to
+connect by some intelligible bond. This can be done, as it seems to me, if
+we make the following assumptions; if the first and chief one be not
+rejected, the others, from being supported by various physiological
+considerations, will not appear very improbable. It is almost universally
+admitted that cells, or the units of the body, propagate themselves by
+self-division or proliferation, retaining the same nature, and ultimately
+becoming converted into the various tissues and substances of the body. But
+besides this means of increase I assume that cells, before their conversion
+into completely passive or "formed material," throw off minute granules or
+atoms, which circulate freely throughout the system, and when supplied with
+proper nutriment multiply by self-division, subsequently becoming developed
+into cells like those from which they were derived. These granules for the
+sake of distinctness may be called cell-gemmules, or, as the cellular
+theory is not fully established, simply gemmules. They are supposed to be
+transmitted from the parents to the offspring, and are generally developed
+in the generation which immediately succeeds, but are often transmitted in
+a dormant state during many generations and are then developed. Their
+development is supposed to depend on their union with other partially
+developed cells or gemmules which precede them in the regular course of
+growth. Why I use the term union, will be seen when we discuss the direct
+action of pollen on the tissues of the mother-plant. Gemmules are supposed
+to be thrown off by every cell or unit, not only during the adult state,
+but during all the stages of development. Lastly, I assume that the
+gemmules in their dormant state have a mutual affinity for each other,
+leading to their aggregation either into buds or into the sexual elements.
+Hence, speaking strictly, it is not the reproductive elements, nor the
+buds, which generate new organisms, but the cells themselves throughout the
+body. These assumptions constitute the provisional hypothesis which I have
+called Pangenesis. Nearly {375} similar views have been propounded, as I
+find, by other authors, more especially by Mr. Herbert Spencer;[902] but
+they are here modified and amplified.
+
+{376}
+
+Before proceeding to show, firstly, how far these assumptions are in
+themselves probable, and secondly, how far they connect and explain the
+various groups of facts with which we are concerned, it may be useful to
+give an illustration of the hypothesis. If one of the simplest Protozoa be
+formed, as appears under the microscope, of a small mass of homogeneous
+gelatinous matter, a minute atom thrown off from any part and nourished
+under favourable circumstances would naturally reproduce the whole; but if
+the upper and lower surfaces were to differ in texture from the central
+portion, then all three parts would have to throw off atoms or gemmules,
+which when aggregated by mutual affinity would form either buds or the
+sexual elements. Precisely the same view may be extended to one of the
+higher animals; although in this case many thousand gemmules must be thrown
+off from the various parts of the body. Now, when the leg, for instance, of
+a salamander is cut off, a slight crust forms over the wound, and beneath
+this crust the uninjured cells or units of bone, muscle, nerves, &c., are
+supposed to unite with the diffused gemmules of those cells which in the
+perfect leg come next in order; and these as they become slightly developed
+unite with others, and so on until a papilla of soft cellular tissue, the
+"budding leg," is formed, and in time a perfect leg.[903] Thus, that
+portion of the leg which had {377} been cut off, neither more nor less,
+would be reproduced. If the tail or leg of a young animal had been cut off,
+a young tail or leg would have been reproduced, as actually occurs with the
+amputated tail of the tadpole; for gemmules of all the units which compose
+the tail are diffused throughout the body at all ages. But during the adult
+state the gemmules of the larval tail would remain dormant, for they would
+not meet with pre-existing cells in a proper state of development with
+which to unite. If from changed conditions or any other cause any part of
+the body should become permanently modified, the gemmules, which are merely
+minute portions of the contents of the cells forming the part, would
+naturally reproduce the same modification. But gemmules previously derived
+from the same part before it had undergone any change, would still be
+diffused throughout the organisation, and would be transmitted from
+generation to generation, so that under favourable circumstances they might
+be redeveloped, and then the new modification would be for a time or for
+ever lost. The aggregation of gemmules derived from every part of the body,
+through their mutual affinity, would form buds, and their aggregation in
+some special manner, apparently in small quantity, together probably with
+the presence of gemmules of certain primordial cells, would constitute the
+sexual elements. By means of these illustrations the hypothesis of
+pangenesis has, I hope, been rendered intelligible.
+
+       *       *       *       *       *
+
+Physiologists maintain, as we have seen, that each cell, though to a large
+extent dependent on others, is likewise, to a certain extent, independent
+or autonomous. I go one small step further, and assume that each cell casts
+off a free gemmule, which is capable of reproducing a similar cell. There
+is some analogy between this view and what we see in compound animals and
+in the flower-buds on the same tree; for these are distinct individuals
+capable of true or seminal reproduction, yet have parts in common and are
+dependent on each other; thus {378} the tree has its bark and trunk, and
+certain corals, as the Virgularia, have not only parts, but movements in
+common.
+
+The existence of free gemmules is a gratuitous assumption, yet can hardly
+be considered as very improbable, seeing that cells have the power of
+multiplication through the self-division of their contents. Gemmules differ
+from true ovules or buds inasmuch as they are supposed to be capable of
+multiplication in their undeveloped state. No one probably will object to
+this capacity as improbable. The blastema within the egg has been known to
+divide and give birth to two embryos; and Thuret[904] has seen the zoospore
+of an alga divide itself, and both halves germinate. An atom of small-pox
+matter, so minute as to be borne by the wind, must multiply itself many
+thousand-fold in a person thus inoculated.[905] It has recently been
+ascertained[906] that a minute portion of the mucous discharge from an
+animal affected with rinderpest, if placed in the blood of a healthy ox,
+increases so fast that in a short space of time "the whole mass of blood,
+weighing many pounds, is infected, and every small particle of that blood
+contains enough poison to give, within less than forty-eight hours, the
+disease to another animal."
+
+The retention of free and undeveloped gemmules in the same body from early
+youth to old age may appear improbable, but we should remember how long
+seeds lie dormant in the earth and buds in the bark of a tree. Their
+transmission from generation to generation may appear still more
+improbable; but here again we should remember that many rudimentary and
+useless organs are transmitted and have been transmitted during an
+indefinite number of generations. We shall presently see how well the
+long-continued transmission of undeveloped gemmules explains many facts.
+
+As each unit, or group of similar units throughout the body, casts off its
+gemmules, and as all are contained within the smallest egg or seed, and
+within each spermatozoon or pollen-grain, their number and minuteness must
+be something {379} inconceivable. I shall hereafter recur to this
+objection, which at first appears so formidable; but it may here be
+remarked that a cod-fish has been found to produce 4,872,000 eggs, a single
+Ascaris about 64,000,000 eggs, and a single Orchidaceous plant probably as
+many million seeds.[907] In these several cases, the spermatozoa and
+pollen-grains must exist in considerably larger numbers. Now, when we have
+to deal with numbers such as these, which the human intellect cannot grasp,
+there is no good reason for rejecting our present hypothesis on account of
+the assumed existence of cell-gemmules a few thousand times more numerous.
+
+The gemmules in each organism must be thoroughly diffused; nor does this
+seem improbable considering their minuteness, and the steady circulation of
+fluids throughout the body. So it must be with the gemmules of plants, for
+with certain kinds even a minute fragment of a leaf will reproduce the
+whole. But a difficulty here occurs; it would appear that with plants, and
+probably with compound animals, such as corals, the gemmules do not spread
+from bud to bud, but only through the tissues developed from each separate
+bud. We are led to this conclusion from the stock being rarely affected by
+the insertion of a bud or graft from a distinct variety. This non-diffusion
+of the gemmules is still more plainly shown in the case of ferns; for Mr.
+Bridgman[908] has proved that, when spores (which it should be remembered
+are of the nature of buds) are taken from a monstrous part of a frond, and
+others from an ordinary part, {380} each reproduces the form of the part
+whence derived. But this non-diffusion of the gemmules from bud to bud may
+be only apparent, depending, as we shall hereafter see, on the nature of
+the first-formed cells in the buds.
+
+The assumed elective affinity of each gemmule for that particular cell
+which precedes it in the order of development is supported by many
+analogies. In all ordinary cases of sexual reproduction the male and female
+elements have a mutual affinity for each other: thus, it is believed that
+about ten thousand species of Compositae exist, and there can be no doubt
+that if the pollen of all these species could be, simultaneously or
+successively, placed on the stigma of any one species, this one would elect
+with unerring certainty its own pollen. This elective capacity is all the
+more wonderful, as it must have been acquired since the many species of
+this great group of plants branched off from a common progenitor. On any
+view of the nature of sexual reproduction, the protoplasm contained within
+the ovules and within the sperm-cells (or the "spermatic force" of the
+latter, if so vague a term be preferred) must act on each other by some law
+of special affinity, either during or subsequently to impregnation, so that
+corresponding parts alone affect each other; thus, a calf produced from a
+short-horned cow by a long-horned bull has its horns and not its horny
+hoofs affected by the union of the two forms, and the offspring from two
+birds with differently coloured tails have their tails and not their whole
+plumage affected.
+
+The various tissues of the body plainly show, as many physiologists have
+insisted,[909] an affinity for special organic substances, whether natural
+or foreign to the body. We see this in the cells of the kidneys attracting
+urea from the blood; in the worrara poison affecting the nerves; upas and
+digitalis the muscles; the Lytta vesicatoria the kidneys; and in the
+poisonous matter of many diseases, as small-pox, scarlet-fever,
+hooping-cough, glanders, cancer, and hydrophobia, affecting certain
+definite parts of the body or certain tissues or glands.
+
+The affinity of various parts of the body for each other during {381} their
+early development was shown in the last chapter, when discussing the
+tendency to fusion in homologous parts. This affinity displays itself in
+the normal fusion of organs which are separate at an early embryonic age,
+and still more plainly in those marvellous cases of double monsters in
+which each bone, muscle, vessel, and nerve in the one embryo, blends with
+the corresponding part in the other. The affinity between homologous organs
+may come into action with single parts, or with the entire individual, as
+in the case of flowers or fruits which are symmetrically blended together
+with all their parts doubled, but without any other trace of fusion.
+
+It has also been assumed that the development of each gemmule depends on
+its union with another cell or unit which has just commenced its
+development, and which, from preceding it in order of growth, is of a
+somewhat different nature. Nor is it a very improbable assumption that the
+development of a gemmule is determined by its union with a cell slightly
+different in nature, for abundant evidence was given in the seventeenth
+chapter, showing that a slight degree of differentiation in the male and
+female sexual elements favours in a marked manner their union and
+subsequent development. But what determines the development of the gemmules
+of the first-formed or primordial cell in the unimpregnated ovule, is
+beyond conjecture.
+
+It must also be admitted that analogy fails to guide us towards any
+determination on several other points: for instance, whether cells, derived
+from the same parent-cell, may, in the regular course of growth, become
+developed into different structures, from absorbing peculiar kinds of
+nutriment, independently of their union with distinct gemmules. We shall
+appreciate this difficulty if we call to mind, what complex yet symmetrical
+growths the cells of plants yield when they are inoculated by the poison of
+a gall-insect. With animals various polypoid excrescences and tumours are
+now generally admitted[910] to be the direct product, through
+proliferation, of normal cells which have become abnormal. In the regular
+growth and repair of bones, the tissues undergo, as Virchow remarks,[911] a
+whole series of permutations and substitutions. "The cartilage-cells may be
+{382} converted by a direct transformation into marrow-cells, and continue
+as such; or they may first be converted into osseous and then into
+medullary tissue; or lastly, they may first be converted into marrow and
+then into bone. So variable are the permutations of these tissues, in
+themselves so nearly allied, and yet in their external appearance so
+completely distinct." But as these tissues thus change their nature at any
+age, without any obvious change in their nutrition, we must suppose in
+accordance with our hypothesis that gemmules derived from one kind of
+tissue combine with the cells of another kind, and cause the successive
+modifications.
+
+It is useless to speculate at what period of development each organic unit
+casts off its gemmules; for the whole subject of the development of the
+various elemental tissues is as yet involved in much doubt. Some
+physiologists, for instance, maintain that muscle or nerve-fibres are
+developed from cells, which are afterwards nourished by their own proper
+powers of absorption; whilst other physiologists deny their cellular
+origin; and Beale maintains that such fibres are renovated exclusively by
+the conversion of fresh germinal matter (that is the so-called nuclei) into
+"formed material." However this may be, it appears probable that all
+external agencies, such as changed nutrition, increased use or disuse, &c.,
+which induced any permanent modification in a structure, would at the same
+time or previously act on the cells, nuclei, germinal or formative matter,
+from which the structures in question were developed, and consequently
+would act on the gemmules or cast-off atoms.
+
+There is another point on which it is useless to speculate, namely, whether
+all gemmules are free and separate, or whether some are from the first
+united into small aggregates. A feather, for instance, is a complex
+structure, and, as each separate part is liable to inherited variations, I
+conclude that each feather certainly generates a large number of gemmules;
+but it is possible that these may be aggregated into a compound gemmule.
+The same remark applies to the petals of a flower, which in some cases are
+highly complex, with each ridge and hollow contrived for special purposes,
+so that each part must have been separately modified, and the modifications
+transmitted; consequently, separate gemmules, according to our hypothesis,
+{383} must have been thrown off from each cell or part. But, as we
+sometimes see half an anther or a small portion of a filament becoming
+petaliform, or parts or mere stripes of the calyx assuming the colour and
+texture of the corolla, it is probable that with petals the gemmules of
+each cell are not aggregated together into a compound gemmule, but are
+freely and separately diffused.
+
+       *       *       *       *       *
+
+Having now endeavoured to show that the several foregoing assumptions are
+to a certain extent supported by analogous facts, and having discussed some
+of the most doubtful points, we will consider how far the hypothesis brings
+under a single point of view the various cases enumerated in the First
+Part. All the forms of reproduction graduate into each other and agree in
+their product; for it is impossible to distinguish between organisms
+produced from buds, from self-division, or from fertilised germs; such
+organisms are liable to variations of the same nature and to reversion of
+character; and as we now see that all the forms of reproduction depend on
+the aggregation of gemmules derived from the whole body, we can understand
+this general agreement. It is satisfactory to find that sexual and asexual
+generation, by both of which widely different processes the same living
+creature is habitually produced, are fundamentally the same.
+Parthenogenesis is no longer wonderful; in fact, the wonder is that it
+should not oftener occur. We see that the reproductive organs do not
+actually create the sexual elements; they merely determine or permit the
+aggregation of the gemmules in a special manner. These organs, together
+with their accessory parts, have, however, high functions to perform; they
+give to both elements a special affinity for each other, independently of
+the contents of the male and female cells, as is shown in the case of
+plants by the mutual reaction of the stigma and pollen-grains; they adapt
+one or both elements for independent temporary existence, and for mutual
+union. The contrivances for these purposes are sometimes wonderfully
+complex, as with the spermatophores of the Cephalopoda. The male element
+sometimes possesses attributes which, if observed in an independent animal,
+would be put down to instinct guided by sense-organs, as when the {384}
+spermatozoon of an insect finds its way into the minute micropyle of the
+egg, or as when the antherozoids of certain algae swim by the aid of their
+ciliae to the female plant, and force themselves into a minute orifice. In
+these latter cases, however, we must believe that the male element has
+acquired its powers, on the same principle with the larvae of animals,
+namely by successive modifications developed at corresponding periods of
+life: we can hardly avoid in these cases looking at the male element as a
+sort of premature larva, which unites, or, like one of the lower algae,
+conjugates, with the female element. What determines the aggregation of the
+gemmules within the sexual organs we do not in the least know; nor do we
+know why buds are formed in certain definite places, leading to the
+symmetrical growth of trees and corals, nor why adventitious buds may be
+formed almost anywhere, even on a petal, and frequently upon healed
+wounds.[912] As soon as the gemmules have aggregated themselves,
+development apparently commences, but in the case of buds is often
+afterwards suspended, and in the case of the sexual elements soon ceases,
+unless the elements of the opposite sexes combine; even after this has
+occurred, the fertilised germ, as with seeds buried in the ground, may
+remain during a lengthened period in a dormant state.
+
+The antagonism which has long been observed,[913] though exceptions
+occur,[914] between active growth and the power of sexual
+reproduction--between the repair of injuries and gemmation--and with
+plants, between rapid increase by buds, rhizomes, &c., and the production
+of seed, is partly explained by the gemmules not existing in sufficient
+numbers for both processes. {385} But this explanation hardly applies to
+those plants which naturally produce a multitude of seeds, but which,
+through a comparatively small increase in the number of the buds on their
+rhizomes or offsets, yield few or no seed. As, however, we shall presently
+see that buds probably include tissue which has already been to a certain
+extent developed or differentiated, some additional organised matter will
+thus have been expended.
+
+From one of the forms of Reproduction, namely, spontaneous self-division,
+we are led by insensible steps to the repair of the slightest injury; and
+the existence of gemmules, derived from every cell or unit throughout the
+body and everywhere diffused, explains all such cases,--even the wonderful
+fact that, when the limbs of the salamander were cut off many times
+successively by Spallanzani and Bonnet, they were exactly and completely
+reproduced. I have heard this process compared with the recrystallisation
+which occurs when the angles of a broken crystal are repaired; and the two
+processes have this much in common, that in the one case the polarity of
+the molecules is the efficient cause, and in the other the affinity of the
+gemmules for particular nascent cells.
+
+Pangenesis does not throw much light on Hybridism, but agrees well with
+most of the ascertained facts. We may conclude from the fact of a single
+spermatozoon or pollen-grain being insufficient for impregnation, that a
+certain number of gemmules derived from each cell or unit are required for
+the development of each part. From the occurrence of parthenogenesis, more
+especially in the case of the silk-moth, in which the embryo is often
+partially formed, we may also infer that the female element includes nearly
+sufficient gemmules of all kinds for independent development, so that when
+united with the male element the gemmules must be superabundant. Now, as a
+general rule, when two species or races are crossed reciprocally, the
+offspring do not differ, and this shows that both sexual elements agree in
+power, in accordance with the view that they include the same gemmules.
+Hybrids and mongrels are generally intermediate in character between the
+two parent-forms, yet occasionally they closely resemble one parent in one
+part and the other parent in another part, or even in their whole
+structure: nor is this difficult to understand on {386} the admission that
+the gemmules in the fertilised germ are superabundant in number, and that
+those derived from one parent have some advantage in number, affinity, or
+vigour over those derived from the other parent. Crossed forms sometimes
+exhibit the colour or other characters of either parent in stripes or
+blotches; and this may occur in the first generation, or through reversion
+in succeeding bud and seminal generations, as in the several instances
+given in the eleventh chapter. In these cases we must follow Naudin,[915]
+and admit that the "essence" or "element" of the two species, which terms I
+should translate into the gemmules, have an affinity for their own kind,
+and thus separate themselves into distinct stripes or blotches; and reasons
+were given, when discussing in the fifteenth chapter the incompatibility of
+certain characters to unite, for believing in such mutual affinity. When
+two forms are crossed, one is not rarely found to be prepotent in the
+transmission of character over the other; and this we can explain only by
+again assuming that the one form has some advantage in the number, vigour,
+or affinity of its gemmules, except in those cases, where certain
+characters are present in the one form and latent in the other. For
+instance, there is a latent tendency in all pigeons to become blue, and,
+when a blue pigeon is crossed with one of any other colour, the blue tint
+is generally prepotent. When we consider latent characters, the explanation
+of this form of prepotency will be obvious.
+
+When one species is crossed with another it is notorious that they do not
+yield the full or proper number of offspring; and we can only say on this
+head that, as the development of each organism depends on such
+nicely-balanced affinities between a host of gemmules and developing cells
+or units, we need not feel at all surprised that the commixture of gemmules
+derived from two distinct species should lead to a partial or complete
+failure of development. With respect to the sterility of hybrids produced
+from the union of two distinct species, it was shown in the nineteenth
+chapter that this depends exclusively on the reproductive organs being
+specially affected; but why these organs should be thus affected we do not
+know, any more than {387} why unnatural conditions of life, though
+compatible with health, should cause sterility; or why continued close
+interbreeding, or the illegitimate unions of dimorphic and trimorphic
+plants, induce the same result. The conclusion that the reproductive organs
+alone are affected, and not the whole organisation, agrees perfectly with
+the unimpaired or even increased capacity in hybrid plants for propagation
+by buds; for this implies, according to our hypothesis, that the cells of
+the hybrids throw off hybridised cell-gemmules, which become aggregated
+into buds, but fail to become aggregated within the reproductive organs, so
+as to form the sexual elements. In a similar manner many plants, when
+placed under unnatural conditions, fail to produce seed, but can readily be
+propagated by buds. We shall presently see that pangenesis agrees well with
+the strong tendency to reversion exhibited by all crossed animals and
+plants.
+
+It was shown in the discussion on graft-hybrids that there is some reason
+to believe that portions of cellular tissue taken from distinct plants
+become so intimately united, as afterwards occasionally to produce crossed
+or hybridised buds. If this fact were fully established, it would, by the
+aid of our hypothesis, connect gemmation and sexual reproduction in the
+closest manner.
+
+Abundant evidence has been advanced proving that pollen taken from one
+species or variety and applied to the stigma of another sometimes directly
+affects the tissues of the mother-plant. It is probable that this occurs
+with many plants during fertilisation, but can only be detected when
+distinct forms are crossed. On any ordinary theory of reproduction this is
+a most anomalous circumstance, for the pollen-grains are manifestly adapted
+to act on the ovule, but in these cases they act on the colour, texture,
+and form of the coats of the seeds, on the ovarium itself, which is a
+modified leaf, and even on the calyx and upper part of the flower-peduncle.
+In accordance with the hypothesis of pangenesis pollen includes gemmules,
+derived from every part of the organisation, which diffuse themselves and
+multiply by self-division; hence it is not surprising that gemmules within
+the pollen, which are derived from the parts near the reproductive organs,
+should sometimes be able to affect the same parts, whilst still undergoing
+development, in the mother-plant. {388}
+
+As, during all the stages of development, the tissues of plants consist of
+cells, and as new cells are not known to be formed between, or
+independently of, pre-existing cells, we must conclude that the gemmules
+derived from the foreign pollen do not become developed merely in contact
+with pre-existing cells, but actually penetrate the nascent cells of the
+mother-plant. This process may be compared with the ordinary act of
+fertilisation, during which the contents of the pollen-tubes penetrate the
+closed embryonic sack within the ovule, and determine the development of
+the embryo. According to this view, the cells of the mother-plant may
+almost literally be said to be fertilised by the gemmules derived from the
+foreign pollen. With all organisms, as we shall presently see, the cells or
+organic units of the embryo during the successive stages of development may
+in like manner be said to be fertilised by the gemmules of the cells, which
+come next in the order of formation.
+
+Animals, when capable of sexual reproduction, are fully developed, and it
+is scarcely possible that the male element should affect the tissues of the
+mother in the same direct manner as with plants; nevertheless it is certain
+that her ovaria are sometimes affected by a previous impregnation, so that
+the ovules subsequently fertilised by a distinct male are plainly
+influenced in character; and this, as in the case of foreign pollen, is
+intelligible through the diffusion, retention, and action of the gemmules
+included within the spermatozoa of the previous male.
+
+Each organism reaches maturity through a longer or shorter course of
+development. The changes may be small and insensibly slow, as when a child
+grows into a man, or many, abrupt, and slight, as in the metamorphoses of
+certain ephemerous insects, or again few and strongly marked, as with most
+other insects. Each part may be moulded within a previously existing and
+corresponding part, and in this case it will appear, falsely as I believe,
+to be formed from the old part; or it may be developed within a wholly
+distinct part of the body, as in the extreme cases of metagenesis. An eye,
+for instance, may be developed at a spot where no eye previously existed.
+We have also seen that allied organic beings in the course of their
+metamorphoses sometimes attain nearly the same structure after passing
+{389} through widely different forms; or conversely, after passing through
+nearly the same early forms, arrive at a widely different termination. In
+these cases it is very difficult to believe that the early cells or units
+possess the inherent power, independently of any external agent, of
+producing new structures wholly different in form, position, and function.
+But these cases become plain on the hypothesis of pangenesis. The organic
+units, during each stage of development, throw off gemmules, which,
+multiplying, are transmitted to the offspring. In the offspring, as soon as
+any particular cell or unit in the proper order of development becomes
+partially developed, it unites with (or to speak metaphorically is
+fertilised by) the gemmule of the next succeeding cell, and so onwards.
+Now, supposing that at any stage of development, certain cells or
+aggregates of cells had been slightly modified by the action of some
+disturbing cause, the cast-off gemmules or atoms of the cell-contents could
+hardly fail to be similarly affected, and consequently would reproduce the
+same modification. This process might be repeated until the structure of
+the part at this particular stage of development became greatly changed,
+but this would not necessarily affect other parts whether previously or
+subsequently developed. In this manner we can understand the remarkable
+independence of structure in the successive metamorphoses, and especially
+in the successive metageneses of many animals.
+
+The term growth ought strictly to be confined to mere increase of size, and
+development to change of structure.[916] Now, a child is said to grow into
+a man, and a foal into a horse, but, as in these cases there is much change
+of structure, the process properly belongs to the order of development. We
+have indirect evidence of this in many variations and diseases supervening
+during so-called growth at a particular period, and being inherited at a
+corresponding period. In the case, however, of diseases which supervene
+during old age, subsequently to the ordinary period of procreation, and
+which nevertheless are sometimes inherited, as occurs with brain and heart
+complaints, we {390} must suppose that the organs were in fact affected at
+an earlier age and threw off at this period affected gemmules; but that the
+affection became visible or injurious only after the prolonged growth of
+the part in the strict sense of the word. In all the changes of structure
+which regularly supervene during old age, we see the effects of
+deteriorated growth, and not of true development.
+
+In the so-called process of _alternate generation_ many individuals are
+generated asexually during very early or later stages of development. These
+individuals may closely resemble the preceding larval form, but generally
+are wonderfully dissimilar. To understand this process we must suppose that
+at a certain stage of development the gemmules are multiplied at an unusual
+rate, and become aggregated by mutual affinity at many centres of
+attraction, or buds. These buds, it may be remarked, must include gemmules
+not only of all the succeeding but likewise of all the preceding stages of
+development; for when mature they have the power of transmitting by sexual
+generation gemmules of all the stages, however numerous these may be. It
+was shown in the First Part, at least in regard to animals, that the new
+beings which are thus at any period asexually generated do not retrograde
+in development--that is, they do not pass through those earlier stages,
+through which the fertilised germ of the same animal has to pass; and an
+explanation of this fact was attempted as far as the final or teleological
+cause is concerned. We can likewise understand the proximate cause, if we
+assume, and the assumption is far from improbable, that buds, like
+chopped-up fragments of a hydra, are formed of tissue which has already
+passed through several of the earlier stages of development; for in this
+case their component cells or units would not unite with the gemmules
+derived from the earlier-formed cells, but only with those which came next
+in the order of development. On the other hand, we must believe that, in
+the sexual elements, or probably in the female alone, gemmules of certain
+primordial cells are present; and these, as soon as their development
+commences, unite in due succession with the gemmules of every part of the
+body, from the first to the last period of life.
+
+The principle of the independent formation of each part, in {391} so far as
+its development depends on the union of the proper gemmules with certain
+nascent cells, together with the superabundance of the gemmules derived
+from both parents and self-multiplied, throws light on a widely different
+group of facts, which on any ordinary view of development appears very
+strange. I allude to organs which are abnormally multiplied or transposed.
+Thus gold-fish often have supernumerary fins placed on various parts of
+their bodies. We have seen that, when the tail of a lizard is broken off, a
+double tail is sometimes reproduced, and when the foot of the salamander is
+divided longitudinally, additional digits are occasionally formed. When
+frogs, toads, &c., are born with their limbs doubled, as sometimes occurs,
+the doubling, as Gervais remarks,[917] cannot be due to the complete fusion
+of two embryos, with the exception of the limbs, for the larvae are
+limbless. The same argument is applicable[918] to certain insects produced
+with multiple legs or antennae, for these are metamorphosed from apodal or
+antennaeless larvae. Alphonse Milne-Edwards[919] has described the curious
+case of a crustacean in which one eye-peduncle supported, instead of a
+complete eye, only an imperfect cornea, out of the centre of which a
+portion of an antenna was developed. A case has been recorded[920] of a man
+who had during both dentitions a double tooth in place of the left second
+incisor, and he inherited this peculiarity from his paternal grandfather.
+Several cases are known[921] of additional teeth having been developed in
+the palate, more especially with horses, and in the orbit of the eye.
+Certain breeds of sheep bear a whole crowd of horns on their foreheads.
+Hairs occasionally appear in strange situations, as within the ears of the
+Siamese hairy family; and hairs "quite natural in structure" have been
+observed "within the substance of the brain."[922] As many as five spurs
+have been seen on both legs in certain Game-fowls. In the Polish fowl the
+male is ornamented with a topknot of hackles {392} like those on his neck,
+whilst the female has one of common feathers. In feather-footed pigeons and
+fowls, feathers like those on the wing arise from the outer side of the
+legs and toes. Even the elemental parts of the same feather may be
+transposed; for in the Sebastopol goose, barbules are developed on the
+divided filaments of the shaft.
+
+Analogous cases are of such frequent occurrence with plants that they do
+not strike us with sufficient surprise. Supernumerary petals, stamens, and
+pistils, are often produced. I have seen a leaflet low down in the compound
+leaf of _Vicia sativa_ converted into a tendril, and a tendril possesses
+many peculiar properties, such as spontaneous movement and irritability.
+The calyx sometimes assumes, either wholly or by stripes, the colour and
+texture of the corolla. Stamens are so frequently converted, more or less
+completely, into petals, that such cases are passed over as not deserving
+notice; but as petals have special functions to perform, namely, to protect
+the included organs, to attract insects, and in not a few cases to guide
+their entrance by well-adapted contrivances, we can hardly account for the
+conversion of stamens into petals merely by unnatural or superfluous
+nourishment. Again, the edge of a petal may occasionally be found including
+one of the highest products of the plant, namely the pollen; for instance,
+I have seen in an Ophrys a pollen-mass with its curious structure of little
+packets, united together and to the caudicle by elastic threads, formed
+between the edges of an upper petal. The segments of the calyx of the
+common pea have been observed partially converted into carpels, including
+ovules, and with their tips converted into stigmas. Numerous analogous
+facts could be given.[923]
+
+I do not know how physiologists look at such facts as the foregoing.
+According to the doctrine of pangenesis, the free and superabundant
+gemmules of the transposed organs are developed in the wrong place, from
+uniting with wrong cells or aggregates of cells during their nascent state;
+and this would follow from a slight modification in the elective affinity
+of such cells, or possibly of certain gemmules. Nor ought we to feel much
+surprise at the affinities of cells and gemmules varying {393} under
+domestication, when we remember the many curious cases given, in the
+seventeenth chapter, of cultivated plants which absolutely refuse to be
+fertilised by their own pollen or by that of the same species, but are
+abundantly fertile with pollen of a distinct species; for this implies that
+their sexual elective affinities--and this is the term used by
+Gaertner--have been modified. As the cells of adjoining or homologous parts
+will have nearly the same nature, they will be liable to acquire by
+variation each other's elective affinities; and we can thus to a certain
+extent understand such cases as a crowd of horns on the heads in certain
+sheep, of several spurs on the leg, and of hackles on the head of the fowl,
+and with the pigeon the occurrence of wing-feathers on their legs and of
+membrane between their toes; for the leg is the homologue of the wing. As
+all the organs of plants are homologous and spring from a common axis, it
+is natural that they should be eminently liable to transposition. It ought
+to be observed that when any compound part, such as an additional limb or
+an antenna, springs from a false position, it is only necessary that the
+few first gemmules should be wrongly attached; for these whilst developing
+would attract others in due succession, as in the regrowth of an amputated
+limb. When parts which are homologous and similar in structure, as the
+vertebrae in snakes or the stamens in polyandrous flowers, &c., are
+repeated many times in the same organism, closely allied gemmules must be
+extremely numerous, as well as the points to which they ought to become
+united; and, in accordance with the foregoing views, we can to a certain
+extent understand Isid. Geoffroy St. Hilaire's law, namely, that parts,
+which are already multiple, are extremely liable to vary in number.
+
+The same general principles apply to the fusion of homologous parts; and
+with respect to mere cohesion there is probably always some degree of
+fusion, at least near the surface. When two embryos during their early
+development come into close contact, as both include corresponding
+gemmules, which must be in all respects almost identical in nature, it is
+not surprising that some derived from one embryo and some from the other
+should unite at the point of contact with a single nascent cell or
+aggregate of cells, and thus give rise to a single part or organ. For
+instance, two embryos might thus come to have on their {394} adjoining
+sides a single symmetrical arm, which in one sense will have been formed by
+the fusion of the bones, muscles, &c., belonging to the arms of both
+embryos. In the case of the fish described by Lereboullet, in which a
+double head was seen gradually to fuse into a single one, the same process
+must have taken place, together with the absorption of all the parts which
+had been already formed. These cases are exactly the reverse of those in
+which a part is doubled either spontaneously or after an injury; for in the
+case of doubling, the superabundant gemmules of the same part are
+separately developed in union with adjoining points; whilst in the case of
+fusion the gemmules derived from two homologous parts become mingled and
+form a single part; or it may be that the gemmules from one of two
+adjoining embryos alone become developed.
+
+       *       *       *       *       *
+
+Variability often depends, as I have attempted to show, on the reproductive
+organs being injuriously affected by changed conditions; and in this case
+the gemmules derived from the various parts of the body are probably
+aggregated in an irregular manner, some superfluous and others deficient.
+Whether a superabundance of gemmules, together with fusion during
+development, would lead to the increased size of any part cannot be told;
+but we can see that their partial deficiency, without necessarily leading
+to the entire abortion of the part, might cause considerable modifications;
+for in the same manner as a plant, if its own pollen be excluded, is easily
+hybridised, so, in the case of a cell, if the properly succeeding gemmules
+were absent, it would probably combine easily with other and allied
+gemmules. We see this in the case of imperfect nails growing on the stumps
+of amputated fingers,[924] for the gemmules of the nails have manifestly
+been developed at the nearest point.
+
+In variations caused by the direct action of changed conditions, whether of
+a definite or indefinite nature, as with the fleeces of sheep in hot
+countries, with maize grown in cold countries, with inherited gout, &c.,
+the tissues of the body, according to the doctrine of pangenesis, are
+directly affected by the new conditions, and consequently throw off
+modified gemmules, which are transmitted with their newly acquired
+peculiarities to the offspring. On any ordinary view it is unintelligible
+how changed {395} conditions, whether acting on the embryo, the young or
+adult animal, can cause inherited modifications. It is equally or even more
+unintelligible on any ordinary view, how the effects of the long-continued
+use or disuse of any part, or of changed habits of body or mind, can be
+inherited. A more perplexing problem can hardly be proposed; but on our
+view we have only to suppose that certain cells become at last not only
+functionally but structurally modified; and that these throw off similarly
+modified gemmules. This may occur at any period of development, and the
+modification will be inherited at a corresponding period; for the modified
+gemmules will unite in all ordinary cases with the proper preceding cells,
+and they will consequently be developed at the same period at which the
+modification first arose. With respect to mental habits or instincts, we
+are so profoundly ignorant on the relation between the brain and the power
+of thought that we do not know whether an inveterate habit or trick induces
+any change in the nervous system; but when any habit or other mental
+attribute, or insanity, is inherited, we must believe that some actual
+modification is transmitted;[925] and this implies, according to our
+hypothesis, that gemmules derived from modified nerve-cells are transmitted
+to the offspring.
+
+It is generally, perhaps always, necessary that an organism should be
+exposed during several generations to changed conditions or habits, in
+order that any modification in the structure of the offspring should ensue.
+This may be partly due to the changes not being at first marked enough to
+catch the attention, but this explanation is insufficient; and I can
+account for the fact, only by the assumption, which we shall see under the
+head of reversion is strongly supported, that gemmules derived from each
+cell before it had undergone the least modification are transmitted in
+large numbers to successive generations, but that the gemmules derived from
+the same cells after modification, naturally go on increasing under the
+same favouring conditions, until at last they become sufficiently numerous
+to overpower and supplant the old gemmules.
+
+Another difficulty may be here noticed; we have seen that {396} there is an
+important difference in the frequency, though not in the nature, of the
+variations in plants propagated by sexual and asexual generation. As far as
+variability depends on the imperfect action of the reproductive organs
+under changed conditions, we can at once see why seedlings should be far
+more variable than plants propagated by buds. We know that extremely slight
+causes,--for instance, whether a tree has been grafted or grows on its own
+stock, the position of the seeds within the capsule, and of the flowers on
+the spike,--sometimes suffice to determine the variation of a plant, when
+raised from seed. Now, it is probable, as explained when discussing
+alternate generation, that a bud is formed of a portion of already
+differentiated tissue; consequently an organism thus formed does not pass
+through the earlier phases of development, and cannot be so freely exposed,
+at the age when its structure would be most readily modified, to the
+various causes inducing variability; but it is very doubtful whether this
+is a sufficient explanation of the difficulty.
+
+With respect to the tendency to reversion, there is a similar difference
+between plants propagated from buds and seed. Many varieties, whether
+originally produced from seed or buds, can be securely propagated by buds,
+but generally or invariably revert by seed. So, also, hybridised plants can
+be multiplied to any extent by buds, but are continually liable to
+reversion by seed,--that is, to the loss of their hybrid or intermediate
+character. I can offer no satisfactory explanation of this fact. Here is a
+still more perplexing case: certain plants with variegated leaves, phloxes
+with striped flowers, barberries with seedless fruit, can all be securely
+propagated by the buds on cuttings; but the buds developed from the roots
+of these cuttings almost invariably lose their character and revert to
+their former condition.
+
+Finally, we can see on the hypothesis of pangenesis that variability
+depends on at least two distinct groups of causes. Firstly, on the
+deficiency, superabundance, fusion, and transposition of gemmules, and on
+the redevelopment of those which have long been dormant. In these cases the
+gemmules themselves have undergone no modification; but the mutations in
+the above respects will amply account for much fluctuating {397}
+variability. Secondly, in the cases in which the organisation has been
+modified by changed conditions, the increased use or disuse of parts, or
+any other cause, the gemmules cast off from the modified units of the body
+will be themselves modified, and, when sufficiently multiplied, will be
+developed into new and changed structures.
+
+       *       *       *       *       *
+
+Turning now to Inheritance: if we suppose a homogeneous gelatinous
+protozoon to vary and assume a reddish colour, a minute separated atom we
+aid naturally, as it grew to full size, retain the same colour; and we
+should have the simplest form of inheritance.[926] Precisely the same view
+may be extended to the infinitely numerous and diversified units of which
+the whole body in one of the higher animals is composed; and the separated
+atoms are our gemmules. We have already sufficiently discussed the
+inheritance of the direct effects of changed conditions, and of increased
+use or disuse of parts, and, by implication, the important principle of
+inheritance at corresponding ages. These groups of facts are to a large
+extent intelligible on the hypothesis of pangenesis, and on no other
+hypothesis as yet advanced.
+
+A few words must be added on the complete abortion or suppression of
+organs. When a part becomes diminished by disuse prolonged during many
+generations, the principle of economy of growth, as previously explained,
+will tend to reduce it still further; but this will not account for the
+complete or almost complete obliteration of, for instance, a minute papilla
+of cellular tissue representing a pistil, or of a microscopically minute
+nodule of bone representing a tooth. In certain cases of suppression not
+yet completed, in which a rudiment occasionally reappears through
+reversion, diffused gemmules derived from this part must, according to our
+view, still exist; hence we must suppose that the cells, in union with
+which the rudiment was formerly developed, in these cases fail in their
+affinity for such gemmules. But in the cases of complete and final abortion
+the gemmules themselves no doubt have perished; nor is this {398} in any
+way improbable, for, though a vast number of active and long-dormant
+gemmules are diffused and nourished in each living creature, yet there must
+be some limit to their number; and it appears natural that gemmules derived
+from an enfeebled and useless rudiment would be more liable to perish than
+those derived from other parts which are still in full functional activity.
+
+With respect to mutilations, it is certain that a part may be removed or
+injured during many generations, and no inherited result follow; and this
+is an apparent objection to the hypothesis which will occur to every one.
+But, in the first place, a being can hardly be intentionally mutilated
+during its early stages of growth whilst in the womb or egg; and such
+mutilations, when naturally caused, would appear like congenital
+deficiencies, which are occasionally inherited. In the second place,
+according to our hypothesis, gemmules multiply by self-division and are
+transmitted from generation to generation; so that during a long period
+they would be present and ready to reproduce a part which was repeatedly
+amputated. Nevertheless it appears, from the facts given in the twelfth
+chapter, that in some rare cases mutilations have been inherited, but in
+most of these the mutilated surface became diseased. In this case it may be
+conjectured that the gemmules of the lost part were gradually all attracted
+by the partially diseased surface, and thus perished. Although this would
+occur in the injured individual alone, and therefore in only one parent,
+yet this might suffice for the inheritance of a mutilation, on the same
+principle that a hornless animal of either sex, when crossed with a perfect
+animal of the opposite sex, often transmits its deficiency.
+
+The last subject that need here be discussed, namely Reversion, rests on
+the principle that transmission and development, though generally acting in
+conjunction, are distinct powers; and the transmission of gemmules and
+their subsequent development show us how the existence of these two
+distinct powers is possible. We plainly see this distinction in the many
+cases in which a grandfather transmits to his grandson, through his
+daughter, characters which she does not, or cannot, possess. Why the
+development of certain characters, not necessarily in any way connected
+with the reproductive organs, should be confined to one sex alone--that is,
+why certain cells in one sex {399} should unite with and cause the
+development of certain gemmules--we do not in the least know; but it is the
+common attribute of most organic beings in which the sexes are separate.
+
+The distinction between transmission and development is likewise seen in
+all ordinary cases of Reversion; but before discussing this subject it may
+be advisable to say a few words on those characters which I have called
+latent, and which would not be classed under Reversion in its usual sense.
+Most, or perhaps all, the secondary characters, which appertain to one sex,
+lie dormant in the other sex; that is, gemmules capable of development into
+the secondary male sexual characters are included within the female; and
+conversely female characters in the male. Why in the female, when her
+ovaria become diseased or fail to act, certain masculine gemmules become
+developed, we do not clearly know, any more than why when a young bull is
+castrated his horns continue growing until they almost resemble those of a
+cow; or why, when a stag is castrated, the gemmules derived from the
+antlers of his progenitors quite fail to be developed. But in many cases,
+with variable organic beings, the mutual affinities of the cells and
+gemmules become modified, so that parts are transposed or multiplied; and
+it would appear that a slight change in the constitution of an animal, in
+connection with the state of the reproductive organs, leads to changed
+affinities in the tissues of various parts of the body. Thus, when male
+animals first arrive at puberty, and subsequently during each recurrent
+season, certain cells or parts acquire an affinity for certain gemmules,
+which become developed into the secondary masculine characters; but if the
+reproductive organs be destroyed, or even temporarily disturbed by changed
+conditions, these affinities are not excited. Nevertheless, the male,
+before he arrives at puberty, and during the season when the species does
+not breed, must include the proper gemmules in a latent state. The curious
+case formerly given of a Hen which assumed the masculine characters, not of
+her own breed but of a remote progenitor, illustrates the connexion between
+latent sexual characters and ordinary reversion. With those animals and
+plants which habitually produce several forms, as with certain butterflies
+described by Mr. Wallace, in which three female forms and {400} the male
+exist, or as with the trimorphic species of Lythrum and Oxalis, gemmules
+capable of reproducing several widely-different forms must be latent in
+each individual.
+
+The same principle of the latency of certain characters, combined with the
+transposition of organs, may be applied to those singular cases of
+butterflies and other insects, in which exactly one half or one quarter of
+the body resembles the male, and the other half or three quarters the
+female; and when this occurs the opposite sides of the body, separated from
+each other by a distinct line, sometimes differ in the most conspicuous
+manner. Again, these same principles apply to the cases given in the
+thirteenth chapter, in which the right and left sides of the body differ to
+an extraordinary degree, as in the spiral winding of certain shells, and as
+in the genus Verruca among cirripedes; for in these cases it is known that
+either side indifferently may undergo the same remarkable change of
+development.
+
+Reversion, in the ordinary sense of the word, comes into action so
+incessantly, that it evidently forms an essential part of the general law
+of inheritance. It occurs with beings, however propagated, whether by buds
+or seminal generation, and sometimes may even be observed in the same
+individual as it advances in age. The tendency to reversion is often
+induced by a change of conditions, and in the plainest manner by the act of
+crossing. Crossed forms are generally at first nearly intermediate in
+character between their two parents; but in the next generation the
+offspring generally revert to one or both of their grandparents, and
+occasionally to more remote ancestors. How can we account for these facts?
+Each organic unit in a hybrid must throw off, according to the doctrine of
+pangenesis, an abundance of hybridised gemmules, for crossed plants can be
+readily and largely propagated by buds; but by the same hypothesis there
+will likewise be present dormant gemmules derived from both pure
+parent-forms; and as these latter retain their normal condition, they
+would, it is probable, be enabled to multiply largely during the lifetime
+of each hybrid. Consequently the sexual elements of a hybrid will include
+both pure and hybridised gemmules; and when two hybrids pair, the
+combination of pure gemmules derived from the one hybrid with the pure
+gemmules of the same parts derived from the other would {401} necessarily
+lead to complete reversion of character; and it is, perhaps, not too bold a
+supposition that unmodified and undeteriorated gemmules of the same nature
+would be especially apt to combine. Pure gemmules in combination with
+hybridised gemmules would lead to partial reversion. And lastly, hybridised
+gemmules derived from both parent-hybrids would simply reproduce the
+original hybrid form.[927] All these cases and degrees of reversion
+incessantly occur.
+
+It was shown in the fifteenth chapter that certain characters are
+antagonistic to each other or do not readily blend together; hence, when
+two animals with antagonistic characters are crossed, it might well happen
+that a sufficiency of gemmules in the male alone for the reproduction of
+his peculiar characters, and in the female alone for the reproduction of
+her peculiar characters, would not be present; and in this case dormant
+gemmules derived from some remote progenitor might easily gain the
+ascendency, and cause the reappearance of long-lost characters. For
+instance, when black and white pigeons, or black and white fowls, are
+crossed,--colours which do not readily blend,--blue plumage in the one
+case, evidently derived from the rock-pigeon, and red plumage in the other
+case, derived from the wild jungle-cock, occasionally reappear. With
+uncrossed breeds the same result would follow, under conditions which
+favoured the multiplication and development of certain dormant gemmules, as
+when animals become feral and revert to their pristine character. A certain
+number of gemmules being requisite for the development of each character,
+as is known to be the case from several spermatozoa or pollen-grains being
+necessary for fertilisation, and time favouring their multiplication, will
+together account for the curious cases, insisted on by Mr. Sedgwick, of
+certain diseases regularly appearing in alternate generations. This
+likewise holds good, more or less strictly, with other weakly inherited
+modifications. Hence, as I have heard it remarked, certain diseases appear
+actually to gain strength by the intermission of a generation. The
+transmission of dormant gemmules during many successive generations is
+hardly in itself more improbable, as {402} previously remarked, than the
+retention during many ages of rudimentary organs, or even only of a
+tendency to the production of a rudiment; but there is no reason to suppose
+that all dormant gemmules would be transmitted and propagated for ever.
+Excessively minute and numerous as they are believed to be, an infinite
+number derived, during a long course of modification and descent, from each
+cell of each progenitor, could not be supported or nourished by the
+organism. On the other hand, it does not seem improbable that certain
+gemmules, under favourable conditions, should be retained and go on
+multiplying for a longer period than others. Finally, on the views here
+given, we certainly gain some clear insight into the wonderful fact that
+the child may depart from the type of both its parents, and resemble its
+grandparents, or ancestors removed by many generations.
+
+_Conclusion._
+
+The hypothesis of Pangenesis, as applied to the several great classes of
+facts just discussed, no doubt is extremely complex; but so assuredly are
+the facts. The assumptions, however, on which the hypothesis rests cannot
+be considered as complex in any extreme degree--namely, that all organic
+units, besides having the power, as is generally admitted, of growing by
+self-division, throw off free and minute atoms of their contents, that is
+gemmules. These multiply and aggregate themselves into buds and the sexual
+elements; their development depends on their union with other nascent cells
+or units; and they are capable of transmission in a dormant state to
+successive generations.
+
+In a highly organised and complex animal, the gemmules thrown off from each
+different cell or unit throughout the body must be inconceivably numerous
+and minute. Each unit of each part, as it changes during development, and
+we know that some insects undergo at least twenty metamorphoses, must throw
+off its gemmules. All organic beings, moreover, include many dormant
+gemmules derived from their grandparents and more remote progenitors, but
+not from all their progenitors. These almost infinitely numerous and minute
+gemmules must be included in each bud, ovule, spermatozoon, and
+pollen-grain. Such an admission will be declared impossible; but, as
+previously {403} remarked, number and size are only relative difficulties,
+and the eggs or seeds produced by certain animals or plants are so numerous
+that they cannot be grasped by the intellect.
+
+The organic particles with which the wind is tainted over miles of space by
+certain offensive animals must be infinitely minute and numerous; yet they
+strongly affect the olfactory nerves. An analogy more appropriate is
+afforded by the contagious particles of certain diseases, which are so
+minute that they float in the atmosphere and adhere to smooth paper; yet we
+know how largely they increase within the human body, and how powerfully
+they act. Independent organisms exist which are barely visible under the
+highest powers of our recently-improved microscopes, and which probably are
+fully as large as the cells or units in one of the higher animals; yet
+these organisms no doubt reproduce themselves by germs of extreme
+minuteness, relatively to their own minute size. Hence the difficulty,
+which at first appears insurmountable, of believing in the existence of
+gemmules so numerous and so small as they must be according to our
+hypothesis, has really little weight.
+
+The cells or units of the body are generally admitted by physiologists to
+be autonomous, like the buds on a tree, but in a less degree. I go one step
+further and assume that they throw off reproductive gemmules. Thus an
+animal does not, as a whole, generate its kind through the sole agency of
+the reproductive system, but each separate cell generates its kind. It has
+often been said by naturalists that each cell of a plant has the actual or
+potential capacity of reproducing the whole plant; but it has this power
+only in virtue of containing gemmules derived from every part. If our
+hypothesis be provisionally accepted, we must look at all the forms of
+asexual reproduction, whether occurring at maturity or as in the case of
+alternate generation during youth, as fundamentally the same, and dependent
+on the mutual aggregation and multiplication of the gemmules. The regrowth
+of an amputated limb or the healing of a wound is the same process
+partially carried out. Sexual generation differs in some important
+respects, chiefly, as it would appear, in an insufficient number of
+gemmules being aggregated within the separate sexual elements, and probably
+in the presence of certain primordial cells. The development of each being,
+including all the {404} forms of metamorphosis and metagenesis, as well as
+the so-called growth of the higher animals, in which structure changes
+though not in a striking manner, depends on the presence of gemmules thrown
+off at each period of life, and on their development, at a corresponding
+period, in union with preceding cells. Such cells may be said to be
+fertilised by the gemmules which come next in the order of development.
+Thus the ordinary act of impregnation and the development of each being are
+closely analogous processes. The child, strictly speaking, does not grow
+into the man, but includes germs which slowly and successively become
+developed and form the man. In the child, as well as in the adult, each
+part generates the same part for the next generation. Inheritance must be
+looked at as merely a form of growth, like the self-division of a
+lowly-organised unicellular plant. Reversion depends on the transmission
+from the forefather to his descendants of dormant gemmules, which
+occasionally become developed under certain known or unknown conditions.
+Each animal and plant may be compared to a bed of mould full of seeds, most
+of which soon germinate, some lie for a period dormant, whilst others
+perish. When we hear it said that a man carries in his constitution the
+seeds of an inherited disease, there is much literal truth in the
+expression. Finally, the power of propagation possessed by each separate
+cell, using the term in its largest sense, determines the reproduction, the
+variability, the development and renovation of each living organism. No
+other attempt, as far as I am aware, has been made, imperfect as this
+confessedly is, to connect under one point of view these several grand
+classes of facts. We cannot fathom the marvellous complexity of an organic
+being; but on the hypothesis here advanced this complexity is much
+increased. Each living creature must be looked at as a microcosm--a little
+universe, formed of a host of self-propagating organisms, inconceivably
+minute and as numerous as the stars in heaven.
+
+       *       *       *       *       *
+
+
+{405}
+
+CHAPTER XXVIII.
+
+CONCLUDING REMARKS.
+
+    DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE
+    AND DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES
+    FAVOURABLE TO SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE
+    QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY
+    PREORDAINED.
+
+As summaries have been added to nearly all the chapters, and as, in the
+chapter on pangenesis, various subjects, such as the forms of reproduction,
+inheritance, reversion, the causes and laws of variability, &c., have been
+recently discussed, I will here only make a few general remarks on the more
+important conclusions which may be deduced from the multifarious details
+given throughout this work.
+
+Savages in all parts of the world easily succeed in taming wild animals;
+and those inhabiting any country or island, when first invaded by man,
+would probably have been still more easily tamed. Complete subjugation
+generally depends on an animal being social in its habits, and on receiving
+man as the chief of the herd or family. Domestication implies almost
+complete fertility under new and changed conditions of life, and this is
+far from being invariably the case. An animal would not have been worth the
+labour of domestication, at least during early times, unless of service to
+man. From these circumstances the number of domesticated animals has never
+been large. With respect to plants, I have shown in the ninth chapter how
+their varied uses were probably first discovered, and the early steps in
+their cultivation. Man could not have known, when he first domesticated an
+animal or plant, whether it would flourish and multiply when transported to
+other countries, therefore he could not have been thus influenced in his
+choice. We see that the close adaptation of the reindeer and camel to
+extremely cold and hot countries has not prevented their domestication.
+Still less {406} could man have foreseen whether his animals and plants
+would vary in succeeding generations and thus give birth to new races; and
+the small capacity of variability in the goose and ass has not prevented
+their domestication from the remotest epoch.
+
+With extremely few exceptions, all animals and plants which have been long
+domesticated, have varied greatly. It matters not under what climate, or
+for what purpose, they are kept, whether as food for man or beast, for
+draught or hunting, for clothing or mere pleasure,--under all these
+circumstances domesticated animals and plants have varied to a much greater
+extent than the forms which in a state of nature are ranked as one species.
+Why certain animals and plants have varied more under domestication than
+others we do not know, any more than why some are rendered more sterile
+than others under changed conditions of life. But we frequently judge of
+the amount of variation by the production of numerous and diversified
+races, and we can clearly see why in many cases this has not occurred,
+namely, because slight successive variations have not been steadily
+accumulated; and such variations will never be accumulated when an animal
+or plant is not closely observed, or much valued, or kept in large numbers.
+
+The fluctuating, and, as far as we can judge, never-ending variability of
+our domesticated productions,--the plasticity of their whole
+organisation,--is one of the most important facts which we learn from the
+numerous details given in the earlier chapters of this work. Yet
+domesticated animals and plants can hardly have been exposed to greater
+changes in their conditions than have many natural species during the
+incessant geological, geographical, and climatal changes of the whole
+world. The former will, however, commonly have been exposed to more sudden
+changes and to less continuously uniform conditions. As man has
+domesticated so many animals and plants belonging to widely different
+classes, and as he certainly did not with prophetic instinct choose those
+species which would vary most, we may infer that all natural species, if
+subjected to analogous conditions, would, on an average, vary to the same
+degree. Few men at the present day will maintain that animals and plants
+were created with a tendency to vary, which long remained dormant, in order
+that fanciers in after ages might {407} rear, for instance, curious breeds
+of the fowl, pigeon, or canary-bird.
+
+From several causes it is difficult to judge of the amount of modification
+which our domestic productions have undergone. In some cases the primitive
+parent-stock has become extinct, or cannot be recognised with certainty
+owing to its supposed descendants having been so much modified. In other
+cases two or more closely allied forms, after being domesticated, have
+crossed; and then it is difficult to estimate how much of the change ought
+to be attributed to variation. But the degree to which our domestic breeds
+have been modified by the crossing of distinct natural forms has probably
+been exaggerated by some authors. A few individuals of one form would
+seldom permanently affect another form existing in much greater numbers;
+for, without careful selection, the stain of the foreign blood would soon
+be obliterated, and during early and barbarous times, when our animals were
+first domesticated, such care would seldom have been taken.
+
+There is good reason to believe that several of the breeds of the dog, ox,
+pig, and of some other animals, are respectively descended from distinct
+wild prototypes; nevertheless the belief in the multiple origin of our
+domesticated animals has been extended by some few naturalists and by many
+breeders to an unauthorised extent. Breeders refuse to look at the whole
+subject under a single point of view; I have heard one, who maintained that
+our fowls were the descendants of at least half-a-dozen aboriginal species,
+protest that he was in no way concerned with the origin of pigeons, ducks,
+rabbits, horses, or any other animal. They overlook the improbability of
+many species having been domesticated at an early and barbarous period.
+They do not consider the improbability of species having existed in a state
+of nature which, if like our present domestic breeds, would have been
+highly abnormal in comparison with all their congeners. They maintain that
+certain species, which formerly existed, have become extinct or unknown,
+although the world is now so much better known. The assumption of so much
+recent extinction is no difficulty in their eyes; for they do not judge of
+its probability by the facility or difficulty of the extinction of other
+closely allied wild forms. Lastly, {408} they often ignore the whole
+subject of geographical distribution as completely as if its laws were the
+result of chance.
+
+Although from the reasons just assigned it is often difficult to judge
+accurately of the amount of change which our domesticated productions have
+undergone, yet this can be ascertained in the cases in which we know that
+all the breeds are descended from a single species, as with the pigeon,
+duck, rabbit, and almost certainly with the fowl; and by the aid of analogy
+this is to a certain extent possible in the case of animals descended from
+several wild stocks. It is impossible to read the details given in the
+earlier chapters, and in many published works, or to visit our various
+exhibitions, without being deeply impressed with the extreme variability of
+our domesticated animals and cultivated plants. I have in many instances
+purposely given details on new and strange peculiarities which have arisen.
+No part of the organisation escapes the tendency to vary. The variations
+generally affect parts of small vital or physiological importance, but so
+it is with the differences which exist between closely allied species. In
+these unimportant characters there is often a greater difference between
+the breeds of the same species than between the natural species of the same
+genus, as Isidore Geoffroy has shown to be the case with size, and as is
+often the case with the colour, texture, form, &c., of the hair, feathers,
+horns, and other dermal appendages.
+
+It has often been asserted that important parts never vary under
+domestication, but this is a complete error. Look at the skull of the pig
+in any one of the highly improved breeds, with the occipital condyles and
+other parts greatly modified; or look at that of the niata ox. Or again, in
+the several breeds of the rabbit, observe the elongated skull, with the
+differently shaped occipital foramen, atlas, and other cervical vertebrae.
+The whole shape of the brain, together with the skull, has been modified in
+Polish fowls; in other breeds of the fowl the number of the vertebrae and
+the forms of the cervical vertebrae have been changed. In certain pigeons
+the shape of the lower jaw, the relative length of the tongue, the size of
+the nostrils and eyelids, the number and shape of the ribs, the form and
+size of the oesophagus, have all varied. In certain quadrupeds the length
+of the intestines has been much increased or {409} diminished. With plants
+we see wonderful differences in the stones of various fruits. In the
+Cucurbitaceae several highly important characters have varied, such as the
+sessile position of the stigmas on the ovarium, the position of the carpels
+within the ovarium, and its projection out of the receptacle. But it would
+be useless to run through the many facts given in the earlier chapters.
+
+It is notorious how greatly the mental disposition, tastes, habits,
+consensual movements, loquacity or silence, and the tone of voice have
+varied and been inherited with our domesticated animals. The dog offers the
+most striking instance of changed mental attributes, and these differences
+cannot be accounted for by descent from distinct wild types. New mental
+characters have certainly often been acquired, and natural ones lost, under
+domestication.
+
+New characters may appear and disappear at any stage of growth, and be
+inherited at a corresponding period. We see this in the difference between
+the eggs of various breeds of the fowl, and in the down on chickens; and
+still more plainly in the differences between the caterpillars and cocoons
+of various breeds of the silk-moth. These facts, simple as they appear,
+throw light on the characters which distinguish the larval and adult states
+of natural species, and on the whole great subject of embryology. New
+characters are liable to become attached exclusively to that sex in which
+they first appeared, or they may be developed in a much higher degree in
+the one than the other sex; or again, after having become attached to one
+sex, they may be partially transferred to the opposite sex. These facts,
+and more especially the circumstance that new characters seem to be
+particularly liable, from some unknown cause, to become attached to the
+male sex, have an important bearing on the acquirement by animals in a
+state of nature of secondary sexual characters.
+
+It has sometimes been said that our domestic productions do not differ in
+constitutional peculiarities, but this cannot be maintained. In our
+improved cattle, pigs, &c., the period of maturity, including that of the
+second dentition, has been much hastened. The period of gestation varies
+much, but has been modified in a fixed manner in only one or two cases. In
+{410} our poultry and pigeons the acquirement of down and of the first
+plumage by the young, and of the secondary sexual characters by the males,
+differ. The number of moults through which the larvae of silk-moths pass,
+varies. The tendency to fatten, to yield much milk, to produce many young
+or eggs at a birth or during life, differs in different breeds. We find
+different degrees of adaptation to climate, and different tendencies to
+certain diseases, to the attacks of parasites, and to the action of certain
+vegetable poisons. With plants, adaptation to certain soils, as with some
+kinds of plums, the power of resisting frost, the period of flowering and
+fruiting, the duration of life, the period of shedding the leaves and of
+retaining them throughout the winter, the proportion and nature of certain
+chemical compounds in the tissues or seeds, all vary.
+
+There is, however, one important constitutional difference between domestic
+races and species; I refer to the sterility which almost invariably
+follows, in a greater or less degree, when species are crossed, and to the
+perfect fertility of the most distinct domestic races, with the exception
+of a very few plants, when similarly crossed. It certainly appears a
+remarkable fact that many closely allied species which in appearance differ
+extremely little should yield when united only a few, more or less sterile
+offspring, or none at all; whilst domestic races which differ conspicuously
+from each other, are when united remarkably fertile, and yield perfectly
+fertile offspring. But this fact is not in reality so inexplicable as it at
+first appears. In the first place, it was clearly shown in the nineteenth
+chapter that the sterility of crossed species does not closely depend on
+differences in their external structure or general constitution, but
+results exclusively from differences in the reproductive system, analogous
+with those which cause the lessened fertility of the illegitimate unions
+and illegitimate offspring of dimorphic and trimorphic plants. In the
+second place, the Pallasian doctrine, that species after having been long
+domesticated lose their natural tendency to sterility when crossed, has
+been shown to be highly probable; we can scarcely avoid this conclusion
+when we reflect on the parentage and present fertility of the several
+breeds of the dog, of Indian and European cattle, sheep, and pigs. Hence it
+would be unreasonable to expect that races formed under domestication {411}
+should acquire sterility when crossed, whilst at the same time we admit
+that domestication eliminates the normal sterility of crossed species. Why
+with closely allied species their reproductive systems should almost
+invariably have been modified in so peculiar a manner as to be mutually
+incapable of acting on each other--though in unequal degrees in the two
+sexes, as shown by the difference in fertility between reciprocal crosses
+in the same species--we do not know, but may with much probability infer
+the cause to be as follows. Most natural species have been habituated to
+nearly uniform conditions of life for an incomparably longer period of time
+than have domestic races; and we positively know that changed conditions
+exert an especial and powerful influence on the reproductive system. Hence
+this difference in habituation may well account for the different action of
+the reproductive organs when domestic races and when species are crossed.
+It is a nearly analogous fact, that most domestic races may be suddenly
+transported from one climate to another, or be placed under widely
+different conditions, and yet retain their fertility unimpaired; whilst a
+multitude of species subjected to lesser changes are rendered incapable of
+breeding.
+
+With the exception of fertility, domestic varieties resemble species when
+crossed in transmitting their characters in the same unequal manner to
+their offspring, in being subject to the prepotency of one form over the
+other, and in their liability to reversion. By repeated crosses a variety
+or a species may be made completely to absorb another. Varieties, as we
+shall see when we treat of their antiquity, sometimes inherit their new
+characters almost, or even quite, as firmly as species. With both, the
+conditions leading to variability and the laws governing its nature appear
+to be the same. Domestic varieties can be classed in groups under groups,
+like species under genera, and these under families and orders; and the
+classification may be either artificial,--that is, founded on any arbitrary
+character,--or natural. With varieties a natural classification is
+certainly founded, and with species is apparently founded, on community of
+descent, together with the amount of modification which the forms have
+undergone. The characters by which domestic varieties differ from each
+other are more {412} variable than those distinguishing species, though
+hardly more so than with certain protean species; but this greater degree
+of variability is not surprising, as varieties have generally been exposed
+within recent times to fluctuating conditions of life, are much more liable
+to have been crossed, and are still in many cases undergoing, or have
+recently undergone, modification by man's methodical or unconscious
+selection.
+
+Domestic varieties as a general rule certainly differ from each other in
+less important parts of their organisation than do species; and when
+important differences occur, they are seldom firmly fixed; but this fact is
+intelligible if we consider man's method of selection. In the living animal
+or plant he cannot observe internal modifications in the more important
+organs; nor does he regard them as long as they are compatible with health
+and life. What does the breeder care about any slight change in the molar
+teeth of his pigs, or for an additional molar tooth in the dog; or for any
+change in the intestinal canal or other internal organ? The breeder cares
+for the flesh of his cattle being well marbled with fat, and for an
+accumulation of fat within the abdomen of his sheep, and this he has
+effected. What would the floriculturist care for any change in the
+structure of the ovarium or of the ovules? As important internal organs are
+certainly liable to numerous slight variations, and as these would probably
+be inherited, for many strange monstrosities are transmitted, man could
+undoubtedly effect a certain amount of change in these organs. When he has
+produced any modification in an important part, it has generally been
+unintentionally in correlation with some other conspicuous part, as when he
+has given ridges and protuberances to the skulls of fowls, by attending to
+the form of the comb, and in the case of the Polish fowl to the plume of
+feathers on the head. By attending to the external form of the
+pouter-pigeon, he has enormously increased the size of the oesophagus, and
+has added to the number of the ribs, and given them greater breadth. With
+the carrier-pigeon, by increasing, through steady selection, the wattles on
+the upper mandible, he has greatly modified the form of the lower mandible;
+and so in many other cases. Natural species, on the other hand, have been
+modified exclusively for their own good, to fit them for infinitely {413}
+diversified conditions of life, to avoid enemies of all kinds, and to
+struggle against a host of competitors. Hence, under such complex
+conditions, it would often happen that modifications of the most varied
+kinds, in important as well as in unimportant parts, would be advantageous
+or even necessary; and they would slowly but surely be acquired through the
+survival of the fittest. Various indirect modifications would likewise
+arise through the law of correlated variation.
+
+Domestic breeds often have an abnormal or semi-monstrous character, as the
+Italian greyhound, bulldog, Blenheim spaniel, and bloodhound amongst
+dogs,--some breeds of cattle and pigs, several breeds of the fowl, and the
+chief breeds of the pigeon. The differences between such abnormal breeds
+occur in parts which in closely-allied natural species differ but slightly
+or not at all. This may be accounted for by man's often selecting,
+especially at first, conspicuous and semi-monstrous deviations of
+structure. We should, however, be cautious in deciding what deviations
+ought to be called monstrous: there can hardly be a doubt that, if the
+brush of horse-like hair on the breast of the turkey-cock had first
+appeared on the domesticated bird, it would have been considered a
+monstrosity; the great plume of feathers on the head of the Polish cock has
+been thus designated, though plumes are common with many kinds of birds; we
+might call the wattle or corrugated skin round the base of the beak of the
+English carrier-pigeon a monstrosity, but we do not thus speak of the
+globular fleshy excrescence at the base of the beak of the male _Carpophaga
+oceanica_.
+
+Some authors have drawn a wide distinction between artificial and natural
+breeds; although in extreme cases the distinction is plain, in many other
+cases an arbitrary line has to be drawn. The difference depends chiefly on
+the kind of selection which has been applied. Artificial breeds are those
+which have been intentionally improved by man; they frequently have an
+unnatural appearance, and are especially liable to loss of excellence
+through reversion and continued variability. The so-called natural breeds,
+on the other hand, are those which are now found in semi-civilised
+countries, and which formerly inhabited separate districts in nearly all
+the European kingdoms. They have been rarely acted on by man's {414}
+intentional selection; more frequently, it is probable, by unconscious
+selection, and partly by natural selection, for animals kept in
+semi-civilised countries have to provide largely for their own wants. Such
+natural breeds will also, it may be presumed, have been directly acted on
+to some extent by the differences, though slight, in the surrounding
+physical conditions.
+
+It is a much more important distinction that some breeds have been from
+their first origin modified in so slow and insensible a manner, that if we
+could see their early progenitors we should hardly be able to say when or
+how the breed first arose; whilst other breeds have originated from a
+strongly-marked or semi-monstrous deviation of structure, which, however,
+may subsequently have been augmented by selection. From what we know of the
+history of the racehorse, greyhound, gamecock, &c., and from their general
+appearance, we may feel nearly confident that they were formed by a slow
+process of improvement: and with the carrier-pigeon, as well as with some
+other pigeons, we know that this has been the case. On the other hand, it
+is certain that the ancon and mauchamp breeds of sheep, and almost certain
+that the niata cattle, turnspit and pug-dogs, jumper and frizzled fowls,
+short-faced tumbler pigeons, hook-billed ducks, &c., and with plants a
+multitude of varieties, suddenly appeared in nearly the same state as we
+now see them. The frequency of these cases is likely to lead to the false
+belief that natural species have often originated in the same abrupt
+manner. But we have no evidence of the appearance, or at least of the
+continued procreation, under nature, of abrupt modifications of structure;
+and various general reasons could be assigned against such a belief: for
+instance, without separation a single monstrous variation would almost
+certainly be soon obliterated by crossing.
+
+On the other hand, we have abundant evidence of the constant occurrence
+under nature of slight individual differences of the most diversified
+kinds; and thus we are led to conclude that species have generally
+originated by the natural selection, not of abrupt modifications, but of
+extremely slight differences. This process may be strictly compared with
+the slow and gradual improvement of the racehorse, greyhound, and gamecock.
+As every detail of structure in each species is closely adapted to its
+general {415} habits of life, it will rarely happen that one part alone
+will be modified; but the co-adapted modifications, as formerly shown, need
+not be absolutely simultaneous. Many variations, however, are from the
+first connected by the law of correlation. Hence it follows that even
+closely-allied species rarely or never differ from each other by some one
+character alone; and this same remark applies to a certain extent to
+domestic races; for these, if they differ much, generally differ in many
+respects.
+
+Some naturalists boldly insist[928] that species are absolutely distinct
+productions, never passing by intermediate links into each other; whilst
+they maintain that domestic varieties can always be connected either with
+each other or with their parent-forms. But if we could always find the
+links between the several breeds of the dog, horse, cattle, sheep, pigs,
+&c., the incessant doubts whether they are descended from one or several
+species would not have arisen. The greyhound genus, if such a term may be
+used, cannot be closely connected with any other breed, unless, perhaps, we
+go back to the ancient Egyptian monuments. Our English bulldog also forms a
+very distinct breed. In all these cases crossed breeds must of course be
+excluded, for the most distinct natural species can thus be connected. By
+what links can the Cochin fowl be closely united with others? By searching
+for breeds still preserved in distant lands, and by going back to
+historical records, tumbler-pigeons, carriers, and barbs can be closely
+connected with the parent rock-pigeon; but we cannot thus connect the
+turbit or the pouter. The degree of distinctness between the various
+domestic breeds depends on the amount of modification which they have
+undergone, and especially on the neglect and final extinction of the
+linking, intermediate, and less valued forms.
+
+It has often been argued that no light is thrown, from the admitted changes
+of domestic races, on the changes which natural species are believed to
+undergo, as the former are said to be mere temporary productions, always
+reverting, as soon as they become feral, to their pristine form. This
+argument has been well combated by Mr. Wallace;[929] and full details were
+given in the thirteenth chapter, showing that the tendency to reversion in
+feral {416} animals and plants has been greatly exaggerated, though no
+doubt to a certain extent it exists. It would be opposed to all the
+principles inculcated in this work, if domestic animals, when exposed to
+new conditions and compelled to struggle for their own wants against a host
+of foreign competitors, were not in the course of time in some manner
+modified. It should also be remembered that many characters lie latent in
+all organic beings ready to be evolved under fitting conditions; and in
+breeds modified within recent times the tendency to reversion is
+particularly strong. But the antiquity of various breeds clearly proves
+that they remain nearly constant as long as their conditions of life remain
+the same.
+
+It has been boldly maintained by some authors that the amount of variation
+to which our domestic productions are liable is strictly limited; but this
+is an assertion resting on little evidence. Whether or not the amount in
+any particular direction is fixed, the tendency to general variability
+seems unlimited. Cattle, sheep, and pigs have been domesticated and have
+varied from the remotest period, as shown by the researches of Ruetimeyer
+and others, yet these animals have, within quite recent times, been
+improved in an unparalleled degree; and this implies continued variability
+of structure. Wheat, as we know from the remains found in the Swiss
+lake-habitations, is one of the most anciently cultivated plants, yet at
+the present day new and better varieties occasionally arise. It may be that
+an ox will never be produced of larger size or finer proportions than our
+present animals, or a race-horse fleeter than Eclipse, or a gooseberry
+larger than the London variety; but he would be a bold man who would assert
+that the extreme limit in these respects has been finally attained. With
+flowers and fruit it has repeatedly been asserted that perfection has been
+reached, but the standard has soon been excelled. A breed of pigeons may
+never be produced with a beak shorter than that of the present short-faced
+tumbler, or with one longer than that of the English carrier, for these
+birds have weak constitutions and are bad breeders; but the shortness and
+length of the beak are the points which have been steadily improved during
+at least the last 150 years; and some of the best judges deny that the goal
+has yet been reached. We may, also, reasonably suspect, from what {417} we
+see in natural species of the variability of extremely modified parts, that
+any structure, after remaining constant during a long series of
+generations, would, under new and changed conditions of life, recommence
+its course of variability, and might again be acted on by selection.
+Nevertheless, as Mr. Wallace[930] has recently remarked with much force and
+truth, there must be both with natural and domestic productions a limit to
+change in certain directions; for instance, there must be a limit to the
+fleetness of any terrestrial animal, as this will be determined by the
+friction to be overcome, the weight to be carried, and the power of
+contraction in the muscular fibres. The English racehorse may have reached
+this limit; but it already surpasses in fleetness its own wild progenitor,
+and all other equine species.
+
+It is not surprising, seeing the great difference between many domestic
+breeds, that some few naturalists have concluded that all are descended
+from distinct aboriginal stocks, more especially as the principle of
+selection has been ignored, and the high antiquity of man, as a breeder of
+animals, has only recently become known. Most naturalists, however, freely
+admit that various extremely dissimilar breeds are descended from a single
+stock, although they do not know much about the art of breeding, cannot
+show the connecting links, nor say where and when the breeds arose. Yet
+these same naturalists will declare, with an air of philosophical caution,
+that they can never admit that one natural species has given birth to
+another until they behold all the transitional steps. But fanciers have
+used exactly the same language with respect to domestic breeds; thus an
+author of an excellent treatise says he will never allow that carrier and
+fantail pigeons are the descendants of the wild rock-pigeon, until the
+transitions have "actually been observed, and can be repeated whenever man
+chooses to set about the task." No doubt it is difficult to realise that
+slight changes added up during long centuries can produce such results; but
+he who wishes to understand the origin of domestic breeds or natural
+species must overcome this difficulty.
+
+The causes inducing and the laws governing variability have been so lately
+discussed, that I need here only enumerate the leading points. As
+domesticated organisms are much more {418} liable to slight deviations of
+structure and to monstrosities, than species living under their natural
+conditions, and as widely-ranging species vary more than those which
+inhabit restricted areas, we may infer that variability mainly depends on
+changed conditions of life. We must not overlook the effects of the unequal
+combination of the characters derived from both parents, nor reversion to
+former progenitors. Changed conditions have an especial tendency to render
+the reproductive organs more or less impotent, as shown in the chapter
+devoted to this subject; and these organs consequently often fail to
+transmit faithfully the parental characters. Changed conditions also act
+directly and definitely on the organisation, so that all or nearly all the
+individuals of the same species thus exposed become modified in the same
+manner; but why this or that part is especially affected we can seldom or
+never say. In most cases, however, of the direct action of changed
+conditions, independently of the indirect variability caused by the
+reproductive organs being affected, indefinite modifications are the
+result; in nearly the same manner as exposure to cold or the absorption of
+the same poison affects different individuals in various ways. We have
+reason to suspect that an habitual excess of highly nutritious food, or an
+excess relatively to the wear and tear of the organisation from exercise,
+is a powerful exciting cause of variability. When we see the symmetrical
+and complex outgrowths, caused by a minute atom of the poison of a
+gall-insect, we may believe that slight changes in the chemical nature of
+the sap or blood would lead to extraordinary modifications of structure.
+
+The increased use of a muscle with its various attached parts, and the
+increased activity of a gland or other organ, lead to their increased
+development. Disuse has a contrary effect. With domesticated productions
+organs sometimes become rudimentary through abortion; but we have no reason
+to suppose that this has ever followed from mere disuse. With natural
+species, on the contrary, many organs appear to have been rendered
+rudimentary through disuse, aided by the principle of the economy of
+growth, and by the hypothetical principle discussed in the last chapter,
+namely, the final destruction of the germs or gemmules of such useless
+parts. This difference may be partly {419} accounted for by disuse having
+acted on domestic forms for an insufficient length of time, and partly from
+their exemption from any severe struggle for existence, entailing rigid
+economy in the development of each part, to which all species under nature
+are subjected. Nevertheless the law of compensation or balancement
+apparently affects, to a certain extent, our domesticated productions.
+
+We must not exaggerate the importance of the definite action of changed
+conditions in modifying all the individuals of the same species in the same
+manner, or of use and disuse. As every part of the organisation is highly
+variable, and as variations are so easily selected, both consciously and
+unconsciously, it is very difficult to distinguish between the effects of
+the selection of indefinite variations, and the direct action of the
+conditions of life. For instance, it is possible that the feet of our
+water-dogs, and of the American dogs which have to travel much over the
+snow, may have become partially webbed from the stimulus of widely
+extending their toes; but it is far more probable that the webbing, like
+the membrane between the toes of certain pigeons, spontaneously appeared
+and was afterwards increased by the best swimmers and the best
+snow-travellers being preserved during many generations. A fancier who
+wished to decrease the size of his bantams or tumbler-pigeons would never
+think of starving them, but would select the smallest individuals which
+spontaneously appeared. Quadrupeds are sometimes born destitute of hair,
+and hairless breeds have been formed, but there is no reason to believe
+that this is caused by a hot climate. Within the tropics heat often causes
+sheep to lose their fleeces, and on the other hand wet and cold act as a
+direct stimulus to the growth of hair; it is, however, possible that these
+changes may merely be an exaggeration of the regular yearly change of coat;
+and who will pretend to decide how far this yearly change, or the thick fur
+of arctic animals, or as I may add their white colour, is due to the direct
+action of a severe climate, and how far to the preservation of the best
+protected individuals during a long succession of generations?
+
+Of all the laws governing variability, that of correlation is the most
+important. In many cases of slight deviations of structure as well as of
+grave monstrosities, we cannot even {420} conjecture what is the nature of
+the bond of connexion. But between homologous parts--between the fore and
+hind limbs--between the hair, hoofs, horns, and teeth--we can see that
+parts which are closely similar during their early development, and which
+are exposed to similar conditions, would be liable to be modified in the
+same manner. Homologous parts, from having the same nature, are apt to
+blend together and, when many exist, to vary in number.
+
+Although every variation is either directly or indirectly caused by some
+change in the surrounding conditions, we must never forget that the nature
+of the organisation which is acted on essentially governs the result.
+Distinct organisms, when placed under similar conditions, vary in different
+manners, whilst closely-allied organisms under dissimilar conditions often
+vary in nearly the same manner. We see this in the same modification
+frequently reappearing at long intervals of time in the same variety, and
+likewise in the several striking cases given of analogous or parallel
+varieties. Although some of these latter cases are simply due to reversion,
+others cannot thus be accounted for.
+
+From the indirect action of changed conditions on the organisation, through
+the impaired state of the reproductive organs--from the direct action of
+such conditions (and this will cause the individuals of the same species
+either to vary in the same manner, or differently in accordance with slight
+differences in their constitution)--from the effects of the increased or
+decreased use of parts,--and from correlation,--the variability of our
+domesticated productions is complicated in an extreme degree. The whole
+organisation becomes slightly plastic. Although each modification must have
+its proper exciting cause, and though each is subjected to law, yet we can
+so rarely trace the precise relation between cause and effect, that we are
+tempted to speak of variations as if they spontaneously arose. We may even
+call them accidental, but this must be only in the sense in which we say
+that a fragment of rock dropped from a height owes its shape to accident.
+
+       *       *       *       *       *
+
+It may be worth while briefly to consider the results of the exposure to
+unnatural conditions of a large number of animals of the same species,
+allowed to cross freely, with no selection of any {421} kind; and
+afterwards to consider the results when selection is brought into play. Let
+us suppose that 500 wild rock-pigeons were confined in their native land in
+an aviary, and fed in the same manner as pigeons usually are; and that they
+were not allowed to increase in number. As pigeons propagate so rapidly, I
+suppose that a thousand or fifteen hundred birds would have to be annually
+killed by mere chance. After several generations had been thus reared, we
+may feel sure that some of the young birds would vary, and the variations
+would tend to be inherited; for at the present day slight deviations of
+structure often occur, but, as most breeds are already well established,
+these modifications are rejected as blemishes. It would be tedious even to
+enumerate the multitude of points which still go on varying or have
+recently varied. Many variations would occur in correlation, as the length
+of the wing and tail feathers--the number of the primary wing-feathers, as
+well as the number and breadth of the ribs, in correlation with the size
+and form of the body--the number of the scutellae, with the size of the
+feet--the length of the tongue, with the length of the beak--the size of
+the nostrils and eyelids and the form of lower jaw in correlation with the
+development of wattle--the nakedness of the young with the future colour of
+the plumage--the size of the feet and beak, and other such points. Lastly,
+as our birds are supposed to be confined in an aviary, they would use their
+wings and legs but little, and certain parts of the skeleton, such as the
+sternum and scapulae and the feet, would in consequence become slightly
+reduced in size.
+
+As in our assumed case many birds have to be indiscriminately killed every
+year, the chances are against any new variety surviving long enough to
+breed. And as the variations which arise are of an extremely diversified
+nature, the chances are very great against two birds pairing which have
+varied in the same manner; nevertheless, a varying bird even when not thus
+paired would occasionally transmit its character to its young; and these
+would not only be exposed to the same conditions which first caused the
+variation in question to appear, but would in addition inherit from their
+one modified parent a tendency again to vary in the same manner. So that,
+if the conditions decidedly tended to induce some particular variation, all
+the birds might {422} in the course of time become similarly modified. But
+a far commoner result would be, that one bird would vary in one way and
+another bird in another way; one would be born with a little longer beak,
+and another with a shorter beak; one would gain some black feathers,
+another some white or red feathers. And as these birds would be continually
+intercrossing, the final result would be a body of individuals differing
+from each other slightly in many ways, yet far more than did the original
+rock-pigeons. But there would not be the least tendency to the formation of
+distinct breeds.
+
+If two separate lots of pigeons were to be treated in the manner just
+described, one in England and the other in a tropical country, the two lots
+being supplied with different food, would they, after many generations had
+passed, differ? When we reflect on the cases given in the twenty-third
+chapter, and on such facts as the difference in former times between the
+breeds of cattle, sheep, &c., in almost every district of Europe, we are
+strongly inclined to admit that the two lots would be differently modified
+through the influence of climate and food. But the evidence on the definite
+action of changed conditions is in most cases insufficient; and, with
+respect to pigeons, I have had the opportunity of examining a large
+collection of domesticated birds, sent to me by Sir W. Elliot from India,
+and they varied in a remarkably similar manner with our European birds.
+
+If two distinct breeds were to be confined together in equal numbers, there
+is reason to suspect that they would to a certain extent prefer pairing
+with their own kind; but they would likewise intercross. From the greater
+vigour and fertility of the crossed offspring, the whole body would by this
+means become interblended sooner than would otherwise have occurred. From
+certain breeds being prepotent over others, it does not follow that the
+interblended progeny would be strictly intermediate in character. I have,
+also, proved that the act of crossing in itself gives a strong tendency to
+reversion, so that the crossed offspring would tend to revert to the state
+of the aboriginal rock-pigeon. In the course of time they would probably be
+not much more heterogeneous in character than in our first case, when birds
+of the same breed were confined together. {423}
+
+I have just said that the crossed offspring would gain in vigour and
+fertility. From the facts given in the seventeenth chapter there can be no
+doubt of this; and there can be little doubt, though the evidence on this
+head is not so easily acquired, that long-continued close interbreeding
+leads to evil results. With hermaphrodites of all kinds, if the sexual
+elements of the same individual habitually acted on each other, the closest
+possible interbreeding would be perpetual. Therefore we should bear in mind
+that with all hermaphrodite animals, as far as I can learn, their structure
+permits and frequently necessitates a cross with a distinct individual.
+With hermaphrodite plants we incessantly meet with elaborate and perfect
+contrivances for this same end. It is no exaggeration to assert that, if
+the use of the talons and tusks of a carnivorous animal, or the use of the
+viscid threads of a spider's web, or of the plumes and hooks on a seed may
+be safely inferred from their structure, we may with equal safety infer
+that many flowers are constructed for the express purpose of ensuring a
+cross with a distinct plant. From these various considerations, the
+conclusion arrived at in the chapter just referred to--namely, that great
+good of some kind is derived from the sexual concourse of distinct
+individuals--must be admitted.
+
+To return to our illustration: we have hitherto assumed that the birds were
+kept down to the same number by indiscriminate slaughter; but if the least
+choice be permitted in their preservation and slaughter, the whole result
+will be changed. Should the owner observe any slight variation in one of
+his birds, and wish to obtain a breed thus characterised, he would succeed
+in a surprisingly short time by carefully selecting and pairing the young.
+As any part which has once varied generally goes on varying in the same
+direction, it is easy, by continually preserving the most strongly marked
+individuals, to increase the amount of difference up to a high,
+predetermined standard of excellence. This is methodical selection.
+
+If the owner of the aviary, without any thought of making a new breed,
+simply admired, for instance, short-beaked more than long-beaked birds, he
+would, when he had to reduce the number, generally kill the latter; and
+there can be no doubt that he would thus in the course of time sensibly
+modify his {424} stock. It is improbable, if two men were to keep pigeons
+and act in this manner, that they would prefer exactly the same characters;
+they would, as we know, often prefer directly opposite characters, and the
+two lots would ultimately come to differ. This has actually occurred with
+strains or families of cattle, sheep, and pigeons, which have been long
+kept and carefully attended to by different breeders without any wish on
+their part to form new and distinct sub-breeds. This unconscious kind of
+selection will more especially come into action with animals which are
+highly serviceable to man; for every one tries to get the best dog, horse,
+cow, or sheep, and these animals will transmit more or less surely their
+good qualities to their offspring. Hardly any one is so careless as to
+breed from his worst animals. Even savages, when compelled from extreme
+want to kill some of their animals, would destroy the worst and preserve
+the best. With animals kept for use and not for mere amusement, different
+fashions prevail in different districts, leading to the preservation, and
+consequently to the transmission, of all sorts of trifling peculiarities of
+character. The same process will have been pursued with our fruit-trees and
+vegetables, for the best will always have been the most largely cultivated,
+and will occasionally have yielded seedlings better than their parents.
+
+The different strains, just alluded to, which have been raised by different
+breeders without any wish for such a result, and the unintentional
+modification of foreign breeds in their new homes, both afford excellent
+evidence of the power of unconscious selection. This form of selection has
+probably led to far more important results than methodical selection, and
+is likewise more important under a theoretical point of view from closely
+resembling natural selection. For during this process the best or most
+valued individuals are not separated and prevented crossing with others of
+the same breed, but are simply preferred and preserved; but this inevitably
+leads during a long succession of generations to their increase in number
+and to their gradual improvement; so that finally they prevail to the
+exclusion of the old parent-form.
+
+With our domesticated animals natural selection checks the production of
+races with any injurious deviation of {425} structure. In the case of
+animals kept by savages and semi-civilised people, which have to provide
+largely for their own wants under different circumstances, natural
+selection will probably play a more important part. Hence such animals
+often closely resemble natural species.
+
+As there is no limit to man's desire to possess animals and plants more and
+more useful in any respect, and as the fancier always wishes, from fashion
+running into extremes, to produce each character more and more strongly
+pronounced, there is a constant tendency in every breed, through the
+prolonged action of methodical and unconscious selection, to become more
+and more different from its parent-stock; and when several breeds have been
+produced and are valued for different qualities, to differ more and more
+from each other. This leads to Divergence of Character. As improved
+sub-varieties and races are slowly formed, the older and less improved
+breeds are neglected and decrease in number. When few individuals of any
+breed exist within the same locality, close interbreeding, by lessening
+their vigour and fertility, aids in their final extinction. Thus the
+intermediate links are lost, and breeds which have already diverged gain
+Distinctness of Character.
+
+In the chapters on the Pigeon, it was proved by historical details and by
+the existence of connecting sub-varieties in distant lands that several
+breeds have steadily diverged in character, and that many old and
+intermediate sub-breeds have become extinct. Other cases could be adduced
+of the extinction of domestic breeds, as of the Irish wolf-dog, the old
+English hound, and of two breeds in France, one of which was formerly
+highly valued.[931] Mr. Pickering remarks[932] that "the sheep figured on
+the most ancient Egyptian monuments is unknown at the present day; and at
+least one variety of the bullock, formerly known in Egypt, has in like
+manner become extinct." So it has been with some animals, and with several
+plants cultivated by the ancient inhabitants of Europe during the neolithic
+period. In Peru, Von Tschudi[933] found in certain tombs, apparently prior
+to the dynasty of the Incas, two kinds of maize not now known in the
+country. With our flowers and culinary vegetables, {426} the production of
+new varieties and their extinction has incessantly recurred. At the present
+time improved breeds sometimes displace at an extraordinarily rapid rate
+older breeds; as has recently occurred throughout England with pigs. The
+Long-horn cattle in their native home were "suddenly swept away as if by
+some murderous pestilence," by the introduction of Short-horns.[934]
+
+What grand results have followed from the long-continued action of
+methodical and unconscious selection, checked and regulated to a certain
+extent by natural selection, is seen on every side of us. Compare the many
+animals and plants which are displayed at our exhibitions with their
+parent-forms when these are known, or consult old historical records with
+respect to their former state. Almost all our domesticated animals have
+given rise to numerous and distinct races, excepting those which cannot be
+easily subjected to selection--such as cats, the cochineal insect, and the
+hive-bee,--and excepting those animals which are not much valued. In
+accordance with what we know of the process of selection, the formation of
+our many races has been slow and gradual. The man who first observed and
+preserved a pigeon with its oesophagus a little enlarged, its beak a little
+longer, or its tail a little more expanded than usual, never dreamed that
+he had made the first step in the creation of the pouter, carrier, and
+fantail-pigeon. Man can create not only anomalous breeds, but others with
+their whole structure admirably co-ordinated for certain purposes, such as
+the race-horse and dray-horse, or the greyhound. It is by no means
+necessary that each small change of structure throughout the body, leading
+towards excellence, should simultaneously arise and be selected. Although
+man seldom attends to differences in organs which are important under a
+physiological point of view, yet he has so profoundly modified some breeds,
+that assuredly, if found wild, they would be ranked under distinct genera.
+
+The best proof of what selection has effected is perhaps afforded by the
+fact that whatever part or quality in any animal, and more especially in
+any plant, is most valued by man, that part or quality differs most in the
+several races. This result is well seen by comparing the amount of
+difference {427} between the fruits produced by the varieties of the same
+fruit-tree, between the flowers of the varieties in our flower-garden,
+between the seeds, roots, or leaves of our culinary and agricultural
+plants, in comparison with the other and not valued parts of the same
+plants. Striking evidence of a different kind is afforded by the fact
+ascertained by Oswald Heer,[935] namely, that the seeds of a large number
+of plants,--wheat, barley, oats, peas, beans, lentils, poppies,--cultivated
+for their seed by the ancient Lake-inhabitants of Switzerland, were all
+smaller than the seeds of our existing varieties. Ruetimeyer has shown that
+the sheep and cattle which were kept by the earlier Lake-inhabitants were
+likewise smaller than our present breeds. In the middens of Denmark, the
+earliest dog of which the remains have been found was the weakest; this was
+succeeded during the Bronze age by a stronger kind, and this again during
+the Iron age by one still stronger. The sheep of Denmark during the Bronze
+period had extraordinarily slender limbs, and the horse was smaller than
+our present animal.[936] No doubt in these cases the new and larger breeds
+were generally introduced from foreign lands by the immigration of new
+hordes of men. But it is not probable that each larger breed, which in the
+course of time supplanted a previous and smaller breed, was the descendant
+of a distinct and larger species; it is far more probable that the domestic
+races of our various animals were gradually improved in different parts of
+the great Europaeo-Asiatic continent, and thence spread to other countries.
+This fact of the gradual increase in size of our domestic animals is all
+the more striking as certain wild or half-wild animals, such as red-deer,
+aurochs, park-cattle, and boars,[937] have within nearly the same period
+decreased in size.
+
+The conditions favourable to selection by man are,--the closest attention
+being paid to every character,--long-continued perseverance,--facility in
+matching or separating animals,--and especially a large number being kept,
+so that the inferior individuals may be freely rejected or destroyed, and
+the better ones preserved. When many are kept there will also be a {428}
+greater chance of the occurrence of well-marked deviations of structure.
+Length of time is all-important; for as each character, in order to become
+strongly pronounced, has to be augmented by the selection of successive
+variations of the same nature, this can only be effected during a long
+series of generations. Length of time will, also, allow any new feature to
+become fixed by the continued rejection of those individuals which revert
+or vary, and the preservation of those which inherit the new character.
+Hence, although some few animals have varied rapidly in certain respects
+under new conditions of life, as dogs in India and sheep in the West
+Indies, yet all the animals and plants which have produced strongly marked
+races were domesticated at an extremely remote epoch, often before the dawn
+of history. As a consequence of this, no record has been preserved of the
+origin of our chief domestic breeds. Even at the present day new strains or
+sub-breeds are formed so slowly that their first appearance passes
+unnoticed. A man attends to some particular character, or merely matches
+his animals with unusual care, and after a time a slight difference is
+perceived by his neighbours;--the difference goes on being augmented by
+unconscious and methodical selection, until at last a new sub-breed is
+formed, receives a local name, and spreads; but, by this time, its history
+is almost forgotten. When the new breed has spread widely, it gives rise to
+new strains and sub-breeds, and the best of these succeed and spread,
+supplanting other and older breeds; and so always onwards in the march of
+improvement.
+
+When a well-marked breed has once been established, if not supplanted by
+still improving sub-breeds, and if not exposed to greatly changed
+conditions of life, inducing further variability or reversion to long-lost
+characters, it may apparently last for an enormous period. We may infer
+that this is the case from the high antiquity of certain races; but some
+caution is necessary on this head, for the same variation may appear
+independently after long intervals of time, or in distant places. We may
+safely assume that this has occurred with the turnspit-dog which is figured
+on the ancient Egyptian monuments, with the solid-hoofed swine[938]
+mentioned by Aristotle, with five-toed fowls {429} described by Columella,
+and certainly with the nectarine. The dogs represented on the Egyptian
+monuments, about 2000 B.C., show us that some of the chief breeds then
+existed, but it is extremely doubtful whether any are identically the same
+with our present breeds. A great mastiff sculptured on an Assyrian tomb,
+640 B.C., is said to be the same with the dog still imported into the same
+region from Thibet. The true greyhound existed during the Roman classical
+period. Coming down to a later period, we have seen that, though most of
+the chief breeds of the pigeon existed between two and three centuries ago,
+they have not all retained to the present day exactly the same character;
+but this has occurred in certain cases in which improvement was not
+desired, for instance in the case of the Spot or the Indian ground-tumbler.
+
+De Candolle[939] has fully discussed the antiquity of various races of
+plants; he states that the black-seeded poppy was known in the time of
+Homer, the white-seeded sesamum by the ancient Egyptians, and almonds with
+sweet and bitter kernels by the Hebrews; but it does not seem improbable
+that some of these varieties may have been lost and reappeared. One variety
+of barley and apparently one of wheat, both of which were cultivated at an
+immensely remote period by the Lake-inhabitants of Switzerland, still
+exist. It is said[940] that "specimens of a small variety of gourd which is
+still common in the market of Lima were exhumed from an ancient cemetery in
+Peru." De Candolle remarks that, in the books and drawings of the sixteenth
+century, the principal races of the cabbage, turnip, and gourd can be
+recognised; this might have been expected at so late a period, but whether
+any of these plants are absolutely identical with our present sub-varieties
+is not certain. It is, however, said that the Brussels sprout, a variety
+which in some places is liable to degeneration, has remained genuine for
+more than four centuries in the district where it is believed to have
+originated.[941]
+
+       *       *       *       *       *
+
+In accordance with the views maintained by me in this work and elsewhere,
+not only the various domestic races, but the {430} most distinct genera and
+orders within the same great class,--for instance, whales, mice, birds, and
+fishes--are all the descendants of one common progenitor, and we must admit
+that the whole vast amount of difference between these forms of life has
+primarily arisen from simple variability. To consider the subject under
+this point of view is enough to strike one dumb with amazement. But our
+amazement ought to be lessened when we reflect that beings, almost infinite
+in number, during an almost infinite lapse of time, have often had their
+whole organisation rendered in some degree plastic, and that each slight
+modification of structure which was in any way beneficial under excessively
+complex conditions of life, will have been preserved, whilst each which was
+in any way injurious will have been rigorously destroyed. And the
+long-continued accumulation of beneficial variations will infallibly lead
+to structures as diversified, as beautifully adapted for various purposes,
+and as excellently co-ordinated, as we see in the animals and plants all
+around us. Hence I have spoken of selection as the paramount power, whether
+applied by man to the formation of domestic breeds, or by nature to the
+production of species. I may recur to the metaphor given in a former
+chapter: if an architect were to rear a noble and commodious edifice,
+without the use of cut stone, by selecting from the fragments at the base
+of a precipice wedge-formed stones for his arches, elongated stones for his
+lintels, and flat stones for his roof, we should admire his skill and
+regard him as the paramount power. Now, the fragments of stone, though
+indispensable to the architect, bear to the edifice built by him the same
+relation which the fluctuating variations of each organic being bear to the
+varied and admirable structures ultimately acquired by its modified
+descendants.
+
+Some authors have declared that natural selection explains nothing, unless
+the precise cause of each slight individual difference be made clear. Now,
+if it were explained to a savage utterly ignorant of the art of building,
+how the edifice had been raised stone upon stone, and why wedge-formed
+fragments were used for the arches, flat stones for the roof, &c.; and if
+the use of each part and of the whole building were pointed out, it would
+be unreasonable if he declared that nothing had been {431} made clear to
+him, because the precise cause of the shape of each fragment could not be
+given. But this is a nearly parallel case with the objection that selection
+explains nothing, because we know not the cause of each individual
+difference in the structure of each being.
+
+The shape of the fragments of stone at the base of our precipice may be
+called accidental, but this is not strictly correct; for the shape of each
+depends on a long sequence of events, all obeying natural laws; on the
+nature of the rock, on the lines of deposition or cleavage, on the form of
+the mountain which depends on its upheaval and subsequent denudation, and
+lastly on the storm or earthquake which threw down the fragments. But in
+regard to the use to which the fragments may be put, their shape may be
+strictly said to be accidental. And here we are led to face a great
+difficulty, in alluding to which I am aware that I am travelling beyond my
+proper province. An omniscient Creator must have foreseen every consequence
+which results from the laws imposed by Him. But can it be reasonably
+maintained that the Creator intentionally ordered, if we use the words in
+any ordinary sense, that certain fragments of rock should assume certain
+shapes so that the builder might erect his edifice? If the various laws
+which have determined the shape of each fragment were not predetermined for
+the builder's sake, can it with any greater probability be maintained that
+He specially ordained for the sake of the breeder each of the innumerable
+variations in our domestic animals and plants;--many of these variations
+being of no service to man, and not beneficial, far more often injurious,
+to the creatures themselves? Did He ordain that the crop and tail-feathers
+of the pigeon should vary in order that the fancier might make his
+grotesque pouter and fantail breeds? Did He cause the frame and mental
+qualities of the dog to vary in order that a breed might be formed of
+indomitable ferocity, with jaws fitted to pin down the bull for man's
+brutal sport? But if we give up the principle in one case,--if we do not
+admit that the variations of the primeval dog were intentionally guided in
+order that the greyhound, for instance, that perfect image of symmetry and
+vigour, might be formed,--no shadow of reason can be assigned for the
+belief that variations, alike in nature and the result {432} of the same
+general laws, which have been the groundwork through natural selection of
+the formation of the most perfectly adapted animals in the world, man
+included, were intentionally and specially guided. However much we may wish
+it, we can hardly follow Professor Asa Gray in his belief "that variation
+has been led along certain beneficial lines," like a stream "along definite
+and useful lines of irrigation." If we assume that each particular
+variation was from the beginning of all time preordained, the plasticity of
+organisation, which leads to many injurious deviations of structure, as
+well as that redundant power of reproduction which inevitably leads to a
+struggle for existence, and, as a consequence, to the natural selection or
+survival of the fittest, must appear to us superfluous laws of nature. On
+the other hand, an omnipotent and omniscient Creator ordains everything and
+foresees everything. Thus we are brought face to face with a difficulty as
+insoluble as is that of free will and predestination.
+
+       *       *       *       *       *
+
+
+{433}
+
+                  INDEX.
+
+  ABBAS Pacha, a fancier of fantailed pigeons, i. 206.
+  ABBEY, Mr., on grafting, ii. 147;
+    on mignonette, ii. 237.
+  ABBOTT, Mr. Keith, on the Persian tumbler pigeon, i. 150.
+  ABBREVIATION of the facial bones, i. 73.
+  ABORTION of organs, ii. 315-318, 397.
+  ABSORPTION of minority in crossed races, ii. 87-89, 174.
+  ACCLIMATISATION, ii. 305-315;
+    of maize, i. 322.
+  ACERBI, on the fertility of domestic animals in Lapland, ii. 112.
+  _Achatinella_, ii. 53.
+  _Achillea millefolium_, bud variation in, i. 408.
+  _Aconitum napellus_, roots of, innocuous in cold climates, ii. 274.
+  _Acorus calamus_, sterility of, ii. 170.
+  ACOSTA, on fowls in South America at its discovery, i. 237.
+  _Acropera_, number of seeds in, ii. 379.
+  ADAM, Mr., origin of _Cytisus Adami_, i. 390.
+  ADAM, W., on consanguineous marriages, ii. 123.
+  ADAMS, Mr., on hereditary diseases, ii. 7.
+  ADVANCEMENT in scale of organisation, i. 8.
+  _Aegilops triticoides_, observations of Fabre and Godron on, i. 313;
+    increasing fertility of hybrids of, with wheat, ii. 110.
+  _Aesculus flava_ and _rubicunda_, i. 392.
+  _Aesculus pavia_, tendency of, to become double, ii. 168.
+  _Aethusa cynapium_, ii. 337.
+  AFFINITY, sexual elective, ii. 180.
+  AFRICA, white bull from, i. 91;
+    feral cattle in, i. 85;
+    food-plants of savages of, i. 307-309;
+    South, diversity of breeds of cattle in, i. 80;
+    West, change in fleece of sheep in, i. 98.
+  _Agave vivipara_, seeding of, in poor soil, ii. 169.
+  AGE, changes in trees, dependent on, i. 387.
+  AGOUTI, fertility of, in captivity, ii. 152.
+  AGRICULTURE, antiquity of, ii. 243.
+  _Agrostis_, seeds of, used as food, i. 309.
+  AGUARA, i. 26.
+  AINSWORTH, Mr., on the change in the hair of animals at Angora, ii. 278.
+  AKBAR Khan, his fondness for pigeons, i. 205; ii. 204.
+  _Alauda arvensis_, ii. 154.
+  ALBIN, on "Golden Hamburgh" fowls, i. 247;
+    figure of the hook-billed duck, i. 277.
+  ALBINISM, i. 111, ii. 17.
+  ALBINO, negro, attacked by insects, ii. 229.
+  ALBINOES, heredity of, ii. 9.
+  ALBINUS, thickness of the epidermis on the palms of the hands in man, ii.
+      297.
+  ALCO, i. 31, ii. 102.
+  ALDROVANDI, on rabbits, i. 104;
+    description of the nun pigeon, i. 156;
+    on the fondness of the Dutch for pigeons in the seventeenth century, i.
+        205;
+    notice of several varieties of pigeons, i. 207-210;
+    on the breeds of fowls, i. 247;
+    on the origin of the domestic duck, i. 278.
+  ALEFIELD, Dr., on the varieties of peas and their specific unity, i. 326;
+    on the varieties of beans, i. 330.
+  ALEXANDER the Great, his selection of Indian cattle, ii. 202.
+  ALGAE, retrogressive metamorphosis in, ii. 361;
+    division of zoospores of, ii. 378.
+  ALLEN, W., on feral fowls, i. 237; ii. 33.
+  ALLMAN, Professor, on a monstrous _Saxifraga geum_, ii. 166;
+    on the development of the Hydroida, ii. 368.
+  ALMOND, i. 337;
+    antiquity of, ii. 429;
+    bitter, not eaten by mice, ii. 232.
+  _Alnus glutinosa_ and _incana_, hybrids of, ii. 130.
+  ALPACA, selection of, ii. 208.
+  _Althaea rosea_, i. 378, ii. 107.
+  _Amaryllis_, ii. 139.
+  _Amaryllis vittata_, effect of foreign pollen on, i. 400.
+  AMAUROSIS, hereditary, ii. 9.
+  AMERICA, limits within which no useful plants have been furnished by, i.
+      310;
+    colours of feral horses in, i. 60-61;
+    North, native cultivated plants of, i. 312;
+    skin of feral pig from, i. 77;
+    South, variations in cattle of, i. 88, 92.
+  _Amygdalus persica_, i. 336-344, 374.
+  {434}
+  AMMON, on the persistency of colour in horses, ii. 21.
+  _Anagallis arvensis_, ii. 190.
+  ANALOGOUS variation, i. 409, ii. 348-352;
+    in horses, i. 55;
+    in the horse and ass, i. 64;
+    in fowls, i. 243-246.
+  _Anas boschas_, i. 277, ii. 40;
+    skull of, figured, i. 282.
+  _Anas moschata_, ii. 40.
+  "ANCON" sheep of Massachusetts, i. 100, ii. 103.
+  ANDALUSIAN fowls, i. 227.
+  ANDALUSIAN rabbits, i. 105.
+  ANDERSON, J., on the origin of British sheep, i. 94;
+    on the selection of qualities in cattle, ii. 196;
+    on a one-eared breed of rabbits, i. 108;
+    on the inheritance of characters from a one-eared rabbit and
+        three-legged bitch, ii. 12;
+    on the persistency of varieties of peas, i. 329;
+    on the production of early peas by selection, ii. 201;
+    on the varieties of the potato, i. 330-331;
+    on crossing varieties of the melon, i. 399;
+    on reversion in the barberry, i. 384.
+  ANDERSON, Mr., on the reproduction of the weeping ash by seed, ii. 19;
+    on the cultivation of the tree paeony in China, ii. 205.
+  ANDERSSON, Mr., on the Damara, Bechuana, and Namaqua cattle, i. 88;
+    on the cows of the Damaras, ii. 300;
+    selection practised by the Damaras and Namaquas, ii. 207;
+    on the use of grass-seeds and the roots of reeds as food in South
+        Africa, i. 309.
+  _Anemone coronaria_, doubled by selection, ii. 200.
+  ANGINA pectoris, hereditary, occurring at a certain age, ii. 79.
+  ANGLESEA, cattle of, i. 80.
+  ANGOLA sheep, i. 95.
+  ANGORA, change in hair of animals at, ii. 278;
+    cats of, i. 45, 47;
+    rabbits of, i. 106, 120.
+  ANIMALS, domestication of, facilitated by fearlessness of man, i. 20;
+    refusal of wild, to breed in captivity, ii. 149;
+    compound, individual peculiarities of, reproduced by budding, i. 374;
+    variation by selection in useful qualities of, ii. 220.
+  ANNUAL plants, rarity of bud-variation in, i. 408.
+  ANOMALIES in the osteology of the horse, i. 50.
+  ANOMALOUS breeds of pigs, i. 75;
+    of cattle, i. 89.
+  _Anser albifrons_, characters of, reproduced in domestic geese, i. 288.
+  _Anser aegyptiacus_, i. 282; ii. 68.
+  _Anser canadensis_, ii. 157.
+  _Anser cygnoides_, i. 237.
+  _Anser ferus_, the original of the domestic goose, i. 287;
+    fertility of cross of, with domestic goose, i. 288.
+  ANSON, on feral fowls in the Ladrones, i. 238.
+  ANTAGONISM between growth and reproduction, ii. 384.
+  _Anthemis nobilis_, bud-variation in flowers of, i. 379;
+    becomes single in poor soil, ii. 167.
+  ANTHEROZOIDS, apparent independence of, in algae, ii. 384.
+  ANTHERS, contabescence of, ii. 165-166.
+  ANTIGUA, cats of, i. 46;
+    changed fleece of sheep in, i. 98.
+  _Antirrhinum majus_, peloric, i. 365; ii. 59, 70, 166;
+    double-flowered, ii. 167;
+    bud-variation in, i. 381.
+  ANTS, individual recognition of, ii. 251.
+  APES, anthropomorphous, ii. 123.
+  APHIDES, attacking pear-trees, ii. 231;
+    development of, ii. 361-362.
+  APOPLEXY, hereditary, occurring at a certain age, ii. 78.
+  APPLE, i. 348-350;
+    fruit of, in Swiss lake-dwellings, i. 317;
+    rendered fastigate by heat in India, i. 361;
+    bud-variation in the, i. 376;
+    with dimidiate fruit, i. 392-393;
+    with two kinds of fruit on the same branch, i. 392;
+    artificial fecundation of, i. 401;
+    St. Valery, i. 401; ii. 166;
+    reversion in seedlings of, ii. 31;
+    crossing of varieties of, ii. 129;
+    growth of the, in Ceylon, ii. 277;
+    Winter Majetin, not attacked by _coccus_, ii. 231;
+    flower-buds of, attacked by bullfinches, ii. 232;
+    American, change of when grown in England, ii. 275.
+  APRICOT, i. 344-345;
+    glands on the leaves of, ii. 231;
+    analogous variation in the, ii. 348.
+  _Aquila fusca_, copulating in captivity, ii. 154.
+  _Aquilegia vulgaris_, i. 365; ii. 330.
+  ARAB boarhound, described by Harcourt, i. 17.
+  _Arabis blepharophylla_ and _A. Soyeri,_ effects of crossing, i. 400.
+  _Aralia trifoliata_, bud-variation in leaves of, i. 382.
+  ARAUCARIAS, young, variable resistance of, to frost, ii. 309.
+  ARCHANGEL pigeon, ii. 240.
+  ARCTIC regions, variability of plants and shells of, ii. 256.
+  _Aria vestita_, grafted on thorns, i. 387.
+  ARISTOPHANES, fowls mentioned by, i. 246.
+  ARISTOTLE, on solid-hoofed pigs, i. 75;
+    domestic duck unknown to, i. 277;
+    on the assumption of male characters by old hens, ii. 51.
+  {435}
+  ARNI, domestication of the, i. 82.
+  ARREST of development, ii. 315-318.
+  ARTERIES, increase of anastomosing branches of, when tied, ii. 230.
+  ARU islands, wild pig of, i. 67.
+  ARUM, Polynesian varieties of, ii. 256.
+  _Ascaris_, number of eggs of, ii. 379.
+  ASH, varieties of the, i. 360;
+    weeping, i. 361;
+    simple-leaved, i. 362;
+    bud-variation in, i. 382;
+    effects of graft upon the stock in the, i. 394;
+    production of the blotched Breadalbane, _ibid._;
+    weeping, capricious reproduction of, by seed, ii. 19.
+  _Asinus Burchellii_, i. 64.
+  _Asinus hemionus_, ii. 43.
+  _Asinus indicus_, ii. 42-43, 48.
+  _Asinus quagga_, i. 64.
+  _Asinus taeniopus_, ii. 41;
+    the original of the domestic ass, i. 62.
+  ASPARAGUS, increased fertility of cultivated, ii. 113.
+  ASS, early domestication of the, i. 62;
+    breeds of, _ibid._;
+    small size of, in India, _ibid._;
+    stripes of, i. 62-63; ii. 351;
+    dislike of to cross water, i. 181;
+    reversion in, ii. 41-43, 47;
+    hybrid of the, with mare and zebra, ii. 42;
+    prepotency of the, over the horse, ii. 67-68;
+    crossed with wild ass, ii. 206;
+    variation and selection of the, ii. 236.
+  ASSYRIAN sculpture of a mastiff, i. 17.
+  ASTERS, ii. 20, 316.
+  ASTHMA, hereditary, ii. 8, 79.
+  ATAVISM. _See_ Reversion.
+  ATHELSTAN, his care of horses, ii. 203.
+  ATKINSON, Mr., on the sterility of the Tarroo silk-moth in confinement,
+      ii. 157.
+  AUBERGINE, ii. 91.
+  AUDUBON, on feral hybrid ducks, i. 190; ii. 46;
+    on the domestication of wild ducks on the Mississippi, i. 278;
+    on the wild cock turkey visiting domestic hens, i. 292;
+    fertility of _Fringilla ciris_ in captivity, ii. 154;
+    fertility of _Columba migratoria_ and _leucocephala_ in captivity, ii.
+        155;
+    breeding of _Anser canadensis_ in captivity, ii. 157.
+  AUDUBON and Bachman, on the change of coat in _Ovis montana_, i. 99;
+    sterility of _Sciurus cinerea_ in confinement, ii. 152.
+  AURICULA, effect of seasonal conditions on the, ii. 273;
+    blooming of, ii. 346.
+  AUSTRALIA, no generally useful plants derived from, i. 310;
+    useful plants of, enumerated by Hooker, i. 311.
+  AUSTRIA, heredity of character in emperors of, ii. 65.
+  AUTENRIETH, on persistency of colour in horses, ii. 21.
+  AVA, horses of, i. 53.
+  _Avena fatua_, cultivability of, i. 313.
+  AYEEN Akbery, pigeons mentioned in the, i. 150, 155, 185, 205, 207, 208.
+  AYRES, W. P., on bud-variation in pelargoniums, i. 378.
+  _Azalea indica_, bud-variation in, i. 377.
+  AZARA, on the feral dogs of La Plata, i. 27;
+    on the crossing of domestic with wild cats in Paraguay, i. 45;
+    on hornlike processes in horses, i. 50;
+    on curled hair in horses, i. 54; ii. 205, 325;
+    on the colours of feral horses, i. 60, 61; ii. 259;
+    on the cattle of Paraguay and La Plata, i. 82, 86, 89; ii. 250;
+    on a hornless bull, ii. 205;
+    on the increase of cattle in South America, ii. 119;
+    on the growth of horns in the hornless cattle of Corrientes, ii. 39;
+    on the "Niata" cattle, i. 90;
+    on naked quadrupeds, ii. 279;
+    on a race of black-skinned fowls in South America, i. 258; ii. 209;
+    on a variety of maize, i. 321.
+
+  BABINGTON, C. C., on the origin of the plum, i. 345;
+    British species of the genus _Rosa_, i. 366;
+    distinctness of _Viola lutea_ and _tricolor_, i. 368.
+  BACHMANN, Mr., on the turkey, ii. 262.
+    _See also_ Audubon.
+  BADGER, breeding in confinement, ii. 151.
+  "BAGADOTTEN-TAUBE," i. 141.
+  BAILY, Mr., on the effect of selection on fowls, ii. 198;
+    on Dorking fowls, ii. 238.
+  BAIRD, S., on the origin of the turkey, i. 292.
+  BAKER, Mr., on heredity in the horse, ii. 11;
+    on the degeneration of the horse by neglect, ii. 239;
+    orders of Henrys VII. and VIII. for the destruction of undersized
+        mares, ii. 203.
+  BAKEWELL, change in the sheep effected by, ii. 198.
+  BALANCEMENT, ii. 342-344;
+    of growth, law of, i. 274.
+  BALDHEAD, pigeon, i. 151.
+  BALDNESS, in man, inherited, ii. 73-74;
+    with deficiency in teeth, ii. 326-327.
+  BALLANCE, Mr., on the effects of interbreeding on fowls, ii. 125;
+    on variation in the eggs of fowls, i. 248.
+  _Ballota nigra_, transmission of variegated leaves in, i. 383.
+  BAMBOO, varieties of the, ii. 256.
+  BANANA, variation of the, i. 372; ii. 256, 258;
+    bud-variation in the, i. 377;
+    sterility of the, ii. 268.
+  BANTAM fowls, i. 230;
+    Sebright, origin of, ii. 96;
+    sterility of, ii. 101.
+  BARB (Pigeon), i. 144-146, 210; ii. 227;
+  {436}
+    figure of, i. 145;
+    figure of lower jaw of, i. 164.
+  BARBS, of wheat, i. 314.
+  BARBERRY, dark or red-leaved variety, i. 362; ii. 19;
+    reversion in suckers of seedless variety, i. 384.
+  BARBUT, J., on the dogs of Guinea, i. 25;
+    on the domestic pigeons in Guinea, i. 186;
+    fowls not native in Guinea, i. 237.
+  BARKING, acquisition of the habit of, by various dogs, i. 27.
+  BARLEY, wild, i. 313;
+    of the lake-dwellings, i. 317-318;
+    ancient variety of, ii. 429.
+  BARNES, Mr., production of early peas by selection, ii. 201.
+  BARNET, Mr., on the intercrossing of strawberries, i. 351;
+    dioeciousness of the Hautbois strawberry, i. 353;
+    on the scarlet American strawberry, ii. 200.
+  BARTH, Dr., use of grass-seeds as food in Central Africa, i. 308.
+  BARTLETT, A. D., on the origin of "Himalayan" rabbits by intercrossing,
+      i. 109;
+    on the feral rabbits of Porto Santo, i. 114;
+    on geese with reversed feathers on the head and neck, i. 288;
+    on the young of the black-shouldered peacock, i. 290;
+    on the breeding of the Felidae in captivity, ii. 150.
+  BARTRAM, on the black wolf-dog of Florida, i. 22.
+  BATES, H. W., refusal of wild animals to breed in captivity, ii. 150,
+      152;
+    sterility of American monkeys in captivity, ii. 153;
+    sterility of tamed guans, ii. 156.
+  BATRACHIA, regeneration of lost parts in, ii. 15.
+  BEACH, raised, in Peru, containing heads of maize, i. 320.
+  BEAK, variability of, in fowls, i. 258;
+    individual differences of, in pigeons, i. 160;
+    correlation of, with the feet in pigeons, i. 171-174.
+  BEALE, Lionel, on the contents of cells, ii. 370;
+    on the multiplication of infectious atoms, ii. 378;
+    on the origin of fibres, ii. 382.
+  BEANS, i. 330;
+    of Swiss lake-dwellings, i. 319;
+    varieties of, produced by selection, ii. 218;
+    French and scarlet, variable resistance of to frost, ii. 309, 314;
+    superiority of native seed of, ii. 314;
+    a symmetrical variation of scarlet, ii. 322;
+    experiments on kidney, i. 330;
+    with monstrous stipules and abortive leaflets, ii. 343.
+  BEARD, pigeon, i. 151.
+  BEARS, breeding in captivity, ii. 151.
+  BEASLEY, J., reversion in crossed cattle, ii. 41.
+  BEATON, D., effect of soil upon strawberries, i. 353;
+    on varieties of pelargonium, i. 364, ii. 274, 311;
+    bud-variation in _Gladiolus colvillii_, i. 382;
+    cross between Scotch kail and cabbage, ii. 98;
+    hybrid gladiolus, ii. 139;
+    constant occurrence of new forms among seedlings, ii. 235;
+    on the doubling of the compositae, ii. 316.
+  BECHUANA cattle, i. 88.
+  BECK, Mr., constitutional differences in pelargoniums, i. 364.
+  BECKMANN, on changes in the odours of plants, ii. 274.
+  BECKSTEIN, on the burrowing of wolves, i. 27;
+    "Spitz" dog, i. 31;
+    origin of the Newfoundland dog, i. 42;
+    crossing of domestic and wild swine, i. 66;
+    on the Jacobin pigeon, i. 154, 209;
+    notice of swallow-pigeons, i. 156;
+    on a fork-tailed pigeon, i. 157;
+    variations in the colour of the croup in pigeons, i. 184;
+    on the German dove-cot pigeon, i. 185;
+    fertility of mongrel pigeons, i. 192;
+    on hybrid turtle-doves, i. 193;
+    on crossing the pigeon with _Columba oenas_, _C. palumbus_, _Turtur
+        risoria_, and _T. vulgaris_, i. 193;
+    development of spurs in the silk-hen, i. 256;
+    on Polish fowls, i. 257, 264;
+    on crested birds, i. 257;
+    on the Canary-bird, i. 295, ii. 22, 161;
+    German superstition about the turkey, i. 293;
+    occurrence of horns in hornless breeds of sheep, ii. 30;
+    hybrids of the horse and ass, ii. 68;
+    crosses of tailless fowls, ii. 92;
+    difficulty of pairing dove-cot and fancy pigeons, ii. 103;
+    fertility of tame ferrets and rabbits, ii. 112;
+    fertility of wild sow, _ibid._;
+    difficulty of breeding caged birds, ii. 154;
+    comparative fertility of _Psittacus erithacus_ in captivity, ii. 155;
+    on changes of plumage in captivity, ii. 158;
+    liability of light-coloured cattle to the attacks of flies, ii. 229;
+    want of exercise a cause of variability, ii. 257;
+    effect of privation of light upon the plumage of birds, ii. 280;
+    on a sub-variety of the monk-pigeon, ii. 350.
+  BEDDOE, Dr., correlation of complexion with consumption, ii. 335.
+  BEDEGUAR gall, ii. 284.
+  BEE, persistency of character of, ii. 236, 254;
+    intercrossing, ii. 126;
+    conveyance, of pollen of peas by, i. 329.
+  BEE-OPHRYS, self-fertilisation of, ii. 91.
+  BEECH, dark-leaved, i. 362, ii. 19;
+    fern-leaved, reversion of, i. 382;
+    weeping, non-production of by seed, ii. 19.
+  BEECHEY, horses of Loochoo Islands, i. 53.
+  BEET, i. 326;
+    increase of sugar in, by selection, ii. 201.
+  {437}
+  _Begonia frigida_, singular variety of, i. 365;
+    sterility of, ii. 166.
+  BELGIAN rabbit, i. 106.
+  BELL, T., statement that white cattle have coloured ears, i. 85.
+  BELL, W., bud-variation in _Cistus tricuspis_, i. 377.
+  BELLINGERI, observations on gestation in the dog, i. 30;
+    on the fertility of dogs and cats, ii. 112.
+  BELON, on high-flying pigeons in Paphlagonia, i. 209;
+    varieties of the goose, i. 289.
+  BENGUELA, cattle of, i. 88.
+  BENNETT, Dr. G., pigs of the Pacific islands, i. 70, 87;
+    dogs of the Pacific islands, i. 87;
+    varieties of cultivated plants in Tahiti, ii. 256.
+  BENNETT, Mr., on the fallow deer, ii. 103.
+  BENTHAM, G., number and origin of cultivated plants, i. 306;
+    cereals all cultivated varieties, i. 312;
+    species of the orange group, i. 334-335;
+    distinctions of almond and peach, i. 338;
+    British species of _Rosa_, i. 366;
+    identity of _Viola lutea_ and _tricolor_, i. 368.
+  _Berberis vulgaris_, i. 384, ii. 19.
+  _Berberis Wallichii_, indifference of, to climate, ii. 164.
+  BERJEAN, on the history of the dog, i. 16, 18.
+  BERKELEY, G. F., production of hen-cocks in a strain of game-fowls, i.
+      253.
+  BERKELEY, M. J., crossing of varieties of the pea, i. 397;
+    effect of foreign pollen on grapes, i. 400;
+    on hybrid plants, ii. 131;
+    analogy between pollen of highly-cultivated plants and hybrids, ii.
+        268;
+    on Hungarian kidney-beans, ii. 275;
+    failure of Indian wheat in England, ii. 307;
+    bud developed on the petal of a _Clarkia_, ii. 384.
+  BERNARD, inheritance of disease in the horse, ii. 10.
+  BERNARD, C., independence of the organs of the body, ii. 368-369;
+    special affinities of the tissues, ii. 380.
+  BERNHARDI, varieties of plants with laciniated leaves, ii. 348.
+  _Bernicla antarctica_, i. 288.
+  BERTERO, on feral pigeons in Juan Fernandez, i. 190.
+  _Betula alba_, ii. 18.
+  BEWICK, on the British wild cattle, i. 84.
+  BIBLE, reference to breeding studs of horses in, i. 54;
+    references to domestic pigeons in the, i. 205;
+    indications of selection of sheep in the, ii. 201;
+    notice of mules in the, ii. 202.
+  BIDWELL, Mr., on self-impotence in _Amaryllis_, ii. 139.
+  BIRCH, weeping, i. 387, ii. 18.
+  BIRCH, Dr. S., on the ancient domestication of the pigeon in Egypt, i.
+      205;
+    notice of bantam fowls in a Japanese encyclopaedia, i. 230, 247.
+  BIRCH, Wyrley, on silver-grey rabbits, i. 109-110.
+  BIRDS, sterility caused in, by change of conditions, ii. 153-157.
+  BLADDER-NUT, tendency of the, to become double, ii. 168.
+  BLAINE, Mr., on wry-legged terriers, ii. 245.
+  BLAINVILLE, origin and history of the dog, i. 15-16;
+    variations in the number of teeth in dogs, i. 34;
+    variations in the number of toes in dogs, i. 35;
+    on mummies of cats, i. 43;
+    on the osteology of solid-hoofed pigs, i. 75;
+    on feral Patagonian and N. American pigs, i. 77.
+  "BLASS-TAUBE," i. 156.
+  BLEEDING, hereditary, ii. 7, 8;
+    sexual limitation of excessive, ii. 73.
+  BLENDING of crossed races, time occupied by the, ii. 87.
+  BLINDNESS, hereditary, ii. 9;
+    at a certain age, ii. 78;
+    associated with colour of hair, ii. 328.
+  BLOODHOUNDS, degeneration of, caused by interbreeding, ii. 121.
+  BLUMENBACH, on the protuberance of the skull in Polish fowls, i. 257;
+    on the effect of circumcision, ii. 23;
+    inheritance of a crooked finger, ii. 23;
+    on badger-dogs and other varieties of the dog, ii. 220;
+    on _Hydra_, ii. 293;
+    on the "nisus formativus," ii. 294.
+  BLYTH, E., on the Pariah dog, i. 24;
+    hybrids of dog and jackal, i. 32;
+    early domestication of cats in India, i. 43;
+    origin of domestic cat, _ib._;
+    crossing of domestic and wild cats, i. 44;
+    on Indian cats resembling _Felis chaus_, i. 45;
+    on striped Burmese ponies, i. 58;
+    on the stripes of the ass, i. 63;
+    on Indian wild pigs, i. 66;
+    on humped cattle, i. 79, 80;
+    occurrence of _Bos frontosus_ in Irish crannoges, i. 81;
+    fertile crossing of zebus and common cattle, i. 83;
+    on the species of sheep, i. 94;
+    on the fat-tailed Indian sheep, i. 96;
+    origin of the goat, i. 101;
+    on rabbits breeding in India, i. 112;
+    number of tail-feathers in fantails, i. 146;
+    Lotan tumbler pigeons, i. 150;
+    number of tail-feathers in _Ectopistes_, i. 159;
+    on _Columba affinis_, i. 183;
+    pigeons roosting in trees, i. 181;
+    on _Columba leuconota_, i. 182;
+    on _Columba intermedia_ of Strickland, i. 184;
+    variation in colour of croup in pigeons, i. 184-185, 197;
+    voluntary domestication of rock-pigeons in India, i. 185;
+    feral pigeons on the Hudson, i. 190;
+  {438}
+    occurrence of sub-species of pigeons, i. 204;
+    notice of pigeon-fanciers in Delhi, &c., i. 206;
+    hybrids of _Gallus Sonneratii_ and the domestic hen, i. 234;
+    supposed hybridity of _Gallus Temminckii_, i. 235;
+    variations and domestication of _Gallus bankiva_, i. 235-236, 237;
+    crossing of wild and tame fowls in Burmah, i. 236;
+    restricted range of the larger gallinaceous birds, i. 237;
+    feral fowls in the Nicobar islands, i. 238;
+    black-skinned fowls occurring near Calcutta, i. 256;
+    weight of _Gallus bankiva_, i. 272;
+    degeneration of the turkey in India, i. 294, ii. 278;
+    on the colour of gold-fish, i. 296;
+    on the Ghor-Khur (_Asinus indicus_), ii. 42;
+    on _Asinus hemionus_, ii. 43;
+    number of eggs of _Gallus bankiva_, ii. 112;
+    on the breeding of birds in captivity, ii. 157;
+    co-existence of large and small breeds in the same country, ii. 279;
+    on the drooping ears of the elephant, ii. 301;
+    homology of leg and wing feathers, ii. 323.
+  BOETHIUS on Scotch wild cattle, i. 85.
+  BOITARD and Corbie, on the breeds of pigeons, i. 132;
+    Lille pouter pigeon, i. 138;
+    notice of a gliding pigeon, i. 156;
+    variety of the pouter pigeon, i. 162;
+    dove-cot pigeon, i. 185;
+    crossing pigeons, i. 192-193, ii. 97, 126;
+    sterility of hybrids of turtle-doves, i. 193;
+    reversion of crossed pigeons, i. 197, ii. 40;
+    on the fantail, i. 208, ii. 66;
+    on the trumpeter, ii. 66;
+    prepotency of transmission in silky fantail, ii. 67, 69;
+    secondary sexual characters in pigeons, ii. 74;
+    crossing of white and coloured turtle-doves, ii. 92;
+    fertility of pigeons, ii. 112.
+  BOMBYCIDAE, wingless females of, ii. 299.
+  _Bombyx hesperus_, ii. 304.
+  _Bombyx Huttoni_, i. 302.
+  _Bombyx mori_, i. 300-304.
+  BONAFOUS, on maize, i. 320, 321.
+  BONAPARTE, number of species of Columbidae, i. 133;
+    number of tail-feathers in pigeons, i. 158;
+    size of the feet in Columbidae, i. 174;
+    on _Columba guinea_, i. 182;
+    _Columba turricola_, _rupestris_, and _Schimperi_, i. 184.
+  _Bonatea speciosa_, development of ovary of, i. 403.
+  BONAVIA, Dr., growth of cauliflowers in India, ii. 310.
+  BONES, removal of portions of, ii. 296;
+    regeneration of, ii. 294;
+    growth and repair of, ii. 381-382.
+  BONNET, on the salamander, ii. 15, 341, 358, 385;
+    theory of reproduction, ii. 385.
+  BORCHMEYER, experiments with the seeds of the weeping ash, ii. 19.
+  BORECOLE, i. 323.
+  BORELLI, on Polish fowls, i. 247.
+  BORNEO, fowls of, with tail-bands, i. 235.
+  BORNET, E., condition of the ovary in hybrid _Cisti_, i. 389;
+    self-impotence of hybrid _Cisti_, ii. 140.
+  BORROW, G., on pointers, i. 42.
+  BORY de Saint-Vincent, on gold-fish, i. 297.
+  _Bos_, probable origin of European domestic cattle from three species of,
+      i. 83.
+  _Bos frontosus_, i. 79, 81-82.
+  _Bos indicus_, i. 79.
+  _Bos longifrons_, i. 79, 81.
+  _Bos primigenius_, i. 79-81, 119.
+  _Bos sondaicus_, ii. 206.
+  _Bos taurus_, i. 79.
+  _Bos trochoceros_, i. 81.
+  BOSC, heredity in foliage-varieties of the elm, i. 362.
+  BOSSE, production of double flowers from old seed, ii. 167.
+  BOSSI, on breeding dark-coloured silkworms, i. 302.
+  BOUCHARDAT, on the vine disease, i. 334.
+  BOUDIN, on local diseases, ii. 276;
+    resistance to cold of dark-complexioned men, ii. 335.
+  "BOULANS," i. 137.
+  "BOUTON d'Alep," ii. 276.
+  BOWEN, Prof., doubts as to the importance of inheritance, ii. 3.
+  BOWMAN, Mr., hereditary peculiarities in the human eye, ii. 8-10;
+    hereditary cataract, ii. 79.
+  BRACE, Mr., on Hungarian cattle, i. 80.
+  _Brachycome iberidifolia_, ii. 261.
+  BRACTS, unusual development of, in gooseberries, i. 355.
+  BRADLEY, Mr., effect of grafts upon the stock in the ash, i. 394;
+    effect of foreign pollen upon apples, i. 401;
+    on change of soil, ii. 146.
+  "BRAHMA Pootras," a new breed of fowls, i. 245.
+  BRAIN, proportion of, in hares and rabbits, i. 126-129.
+  BRANDT, origin of the goat, i. 101.
+  _Brassica_, varieties of, with enlarged stems, ii. 348.
+  _Brassica asperifolia_, ii. 343.
+  _Brassica napus_, i. 325.
+  _Brassica oleracea_, i. 323.
+  _Brassica rapa_, i. 325, ii. 165.
+  BRAUN, A., bud-variation in the vine, i. 375;
+    in the currant, i. 376;
+    in _Mirabilis jalapa_, i. 382;
+    in _Cytisus adami_, i. 388;
+    on reversion in the foliage of trees, i. 382;
+    spontaneous production of _Cytisus purpureo-elongatus_, i. 390;
+    reversion of flowers by stripes and blotches, ii. 37;
+    excess of nourishment a source of variability, ii. 257.
+  {439}
+  BRAZIL, cattle of, i. 88.
+  BREAD-FRUIT, varieties of, ii. 256;
+    sterility and variability of, ii. 262.
+  BREE, W. T., bud-variation in _Geranium pratense_ and _Centaurea cyanus_,
+      i. 379;
+    by tubers in the dahlia, i. 385;
+    on the deafness of white cats with blue eyes, ii. 329.
+  BREEDING, high, dependent on inheritance, ii. 3-4.
+  BREEDS, domestic, persistency of, ii. 246, 428-429;
+    artificial and natural, ii. 413-414;
+    extinction of, ii. 425;
+    of domestic cats, i. 45-47;
+    of pigs produced by crossing, i. 78;
+    of cattle, i. 86-87, 91-93;
+    of goats, i. 101.
+  BREHM, on _Columba amaliae_, i. 183.
+  BRENT, B. P., number of mammae in rabbits, i. 106;
+    habits of the tumbler pigeon, i. 151;
+    Laugher pigeon, i. 155;
+    colouring of the kite tumbler, i. 160;
+    crossing of the pigeon with _Columba oenas_, i. 193;
+    mongrels of the trumpeter pigeon, ii. 66;
+    close interbreeding of pigeons, ii. 126;
+    opinion on Aldrovandi's fowls, i. 247;
+    on stripes in chickens, i. 249-250;
+    on the combs of fowls, i. 253;
+    double-spurred Dorking fowls, i. 255;
+    effect of crossing on colour of plumage in fowls, i. 258;
+    incubatory instinct of mongrels between non-sitting varieties of fowls,
+        ii. 44;
+    origin of the domestic duck, i. 277;
+    fertility of the hook-billed duck, _ibid._;
+    occurrence of the plumage of the wild duck in domestic breeds, i. 280;
+    voice of ducks, i. 281;
+    occurrence of a short upper mandible in crosses of hook-billed and
+        common ducks, i. 281;
+    reversion in ducks produced by crossing, ii. 40;
+    variation of the canary-bird, i. 295;
+    fashion in the canary, ii. 240;
+    hybrids of canary and finches, ii. 45.
+  BRICKELL, on raising nectarines from seed, i. 340;
+    on the horses of North Carolina, ii. 300.
+  BRIDGES, Mr., on the dogs of Tierra del Fuego, i. 39;
+    on the selection of dogs by the Fuegians, ii. 207.
+  BRIDGMAN, W. K., reproduction of abnormal ferns, i. 383, ii. 379.
+  BRIGGS, J. J., regeneration of portions of the fins of fishes, ii. 15.
+  BROCA, P., on the intercrossing of dogs, i. 31-32;
+    on hybrids of hare and rabbit, i. 105;
+    on the rumpless fowl, i. 259;
+    on the character of half-castes, ii. 47;
+    degree of fertility of mongrels, ii. 100;
+    sterility of descendants of wild animals bred in captivity, ii. 160.
+  BROCCOLI, i. 323;
+    rudimentary flowers in, ii. 316;
+    tenderness of, ii. 310.
+  BROMEHEAD, W., doubling of the Canterbury bell by selection, ii. 200.
+  BROMFIELD, Dr., sterility of the ivy and _Acorus calamus_, ii. 170.
+  _Bromus secalinus_, i. 314.
+  BRONN, H. G., bud-variation in _Anthemis_, i. 379;
+    effects of cross-breeding on the female, i. 404;
+    on heredity in a one-horned cow, ii. 12, 13;
+    propagation of a pendulous peach by seed, ii. 18;
+    absorption of the minority in crossed races, ii. 88;
+    on the crossing of horses, ii. 92;
+    fertility of tame rabbits and sheep, ii. 112;
+    changes of plumage in captivity, ii. 158;
+    on the dahlia, ii. 261.
+  BRONZE period, dog of, i. 18.
+  BROWN, G., variations in the dentition of the horse, i. 50.
+  BROWN-SEQUARD, Dr., inheritance of artificially-produced epilepsy in the
+      guinea-pig, ii. 24.
+  _Brunswigia_, ii. 139.
+  BRUSSELS Sprouts, i. 323, ii. 429.
+  _Bubo maximus_, ii. 154.
+  BUCKLAND, F., on oysters, ii. 280;
+    number of eggs in a codfish, ii. 379.
+  BUCKLE, Mr., doubts as to the importance of inheritance, ii. 3.
+  BUCKLEY, Miss, carrier-pigeons roosting in trees, i. 181.
+  BUCKMAN, Prof., cultivation of _Avena fatua_, i. 313;
+    cultivation of the wild parsnip, i. 326, ii. 201, 277;
+    reversion in the parsnip, ii. 31.
+  BUCKWHEAT, injurious to white pigs, when in flower, ii. 337.
+  BUD and seed, close analogy of, i. 411.
+  BUD-REVERSION, ii. 37.
+  BUDS, adventitious, ii. 384.
+  BUD-VARIATION, i. 373-411, ii. 254, 287-288, 291;
+    contrasted with seminal reproduction, i. 373;
+    peculiar to plants, i. 374;
+    in the peach, i. 340, 374;
+    in plums, i. 375;
+    in the cherry, _ibid._;
+    in grapes, _ibid._;
+    in the gooseberry, currant, pear, and apple, i. 376;
+    in the banana, camellia, hawthorn, _Azalea indica_, and _Cistus
+        tricuspis_, i. 377;
+    in the hollyhock and pelargonium, i. 378;
+    in _Geranium pratense_ and the chrysanthemum, i. 379;
+    in roses, i. 367, 379-381;
+    in sweet williams, carnations, pinks, stocks, and snapdragons, i. 381;
+    in wall-flowers, cyclamen, _Oenothera biennis_, _Gladiolus colvillii_,
+        fuchsias, and _Mirabilis jalapa_, i. 382;
+    in foliage of various trees, i. 382-384;
+    in cryptogamic plants, i. 383;
+    by suckers in _Phlox_ and barberry, i. 384;
+    by tubers in the potato, _ibid._;
+    in the dahlia, i. 385;
+    by bulbs in hyacinths, _Imatophyllum miniatum_, and tulips, i. 385;
+    in _Tigridia conchiflora_, i. 386;
+  {440}
+    in _Hemerocallis_, _ibid._;
+    doubtful cases, i. 386-387;
+    in _Cytisus Adami_, i. 387-394;
+    probable in _Aesculus rubicunda_, i. 392;
+    summary of observations on, 406.
+  BUFFON, on crossing the wolf and dog, i. 32;
+    increase of fertility by domestication, ii. 111;
+    improvement of plants by unconscious selection, ii. 216;
+    theory of reproduction, ii. 375.
+  _Bulimus_, ii. 53.
+  BULL, apparent influence of, on offspring, ii. 68.
+  BULLACE, i. 345.
+  BULLDOG, recent modifications of, i. 42.
+  BULLFINCH, breeding in captivity, ii. 154;
+    attacking flower-buds, ii. 232.
+  BULT, Mr., selection of pouter pigeons, ii. 197.
+  "BUENDTNERSCHWEIN," i. 67.
+  BUNTING, reed, in captivity, ii. 158.
+  BURDACH, crossing of domestic and wild animals, i. 66;
+    aversion of the wild boar to barley, ii. 303.
+  BURKE, Mr., inheritance in the horse, ii. 10.
+  _Burlingtonia_, ii. 135.
+  BURMAH, cats of, i. 47.
+  BURMESE ponies, striped, i. 58, 59.
+  BURNES, Sir A., on the Karakool sheep, i. 98, ii. 278;
+    varieties of the vine in Cabool, i. 333;
+    hawks, trained in Scinde, ii. 153;
+    pomegranates producing seed, ii. 168.
+  BURTON Constable, wild cattle at, i. 84.
+  "BURZEL-TAUBEN," i. 150.
+  BUSSORAH carrier, i. 141.
+  _Buteo vulgaris_, copulation of, in captivity, ii. 154.
+  BUTTERFLIES, polymorphic, ii. 399-400.
+  BUZAREINGUES, Girou de, inheritance of tricks, ii. 6.
+
+  CABANIS, pears grafted on the quince, ii. 239.
+  CABBAGE, i. 323-326;
+    varieties of, i. 323;
+    unity of character in flowers and seeds of, i. 323-324;
+    cultivated by ancient Celts, i. 324;
+    classification of varieties of, _ibid._;
+    ready crossing of, _ibid._, ii. 90, 91, 98, 130;
+    origin of, i. 325;
+    increased fertility of, when cultivated, ii. 113;
+    growth of, in tropical countries, ii. 277.
+  CABOOL, vines of, i. 333.
+  CABRAL, on early cultivation in Brazil, i. 311.
+  CACTUS, growth of cochineal on, in India, ii. 275.
+  CAESAR, _Bos primigenius_ wild in Europe in the time of, i. 81;
+    notice of fowls in Britain, i. 246;
+    notice of the importation of horses by the Celts, ii. 203.
+  CAFFRE fowls, i. 230.
+  CAFFRES, different kinds of cattle possessed by the, i. 88.
+  "CAGIAS," a breed of sheep, i. 95.
+  CALCEOLARIAS, i. 364; ii. 147;
+    effects of seasonal conditions on, ii. 274;
+    peloric flowers in, ii. 346.
+  "CALONGOS," a Columbian breed of cattle, i. 88.
+  CALVER, Mr., on a seedling peach producing both peaches and nectarines,
+      i. 341.
+  CALYX, segments of the, converted into carpels, ii. 392.
+  CAMEL, its dislike to crossing water, i. 181.
+  _Camellia_, bud-variations in, i. 377;
+    recognition of varieties of, ii. 251;
+    variety in, hardiness of, ii. 308.
+  CAMERON, D., on the cultivation of Alpine plants, ii. 163.
+  CAMERONN, Baron, value of English blood in race-horses, ii. 11.
+  _Campanula medium_, ii. 200.
+  CANARY-BIRD, i. 295;
+    conditions of inheritance in, ii. 22;
+    hybrids of, ii. 45;
+    period of perfect plumage in, ii. 77;
+    diminished fertility of, ii. 161;
+    standard of perfection in, ii. 195;
+    analogous variation in, ii. 349.
+  CANCER, heredity of, ii. 7, 8, 79.
+  CANINE teeth, development of the, in mares, ii. 318.
+  _Canis alopex_, i. 29.
+  _Canis antarcticus_, i. 20.
+  _Canis argentatus_, ii. 151.
+  _Canis aureus_, i. 29.
+  _Canis cancrivorus_, domesticated and crossed in Guiana, i. 23.
+  _Canis cinereo-variegatus_, i. 29.
+  _Canis fulvus_, i. 29.
+  _Canis Ingae_, the naked Peruvian dog, i. 23.
+  _Canis latrans_, resemblance of, to the Hare Indian dog, i. 22;
+    one of the original stocks, i. 26.
+  _Canis lupaster_, i. 25.
+  _Canis lupus_, var. _occidentalis_, resemblance of, to North American
+      dogs, i. 21;
+    crossed with dogs, i. 22;
+    one of the original stocks, i. 26.
+  _Canis mesomelas_, i. 25, 29.
+  _Canis primaevus_, tamed by Mr. Hodgson, i. 26.
+  _Canis sabbar_, i. 25.
+  _Canis simensis_, possible original of greyhounds, i. 33.
+  _Canis thaleb_, i. 29.
+  _Canis variegatus_, i. 29.
+  CANTERBURY Bell, doubled by selection, ii. 200.
+  CAPE of Good Hope, different kinds of cattle at the, i. 88;
+  {441}
+    no useful plants derived from the, i. 310.
+  CAPERCAILZIE, breeding in captivity, ii. 156.
+  _Capra aegagrus_ and _C. Falconeri_, probable parents of domestic goat,
+      i. 101.
+  CAPSICUM, i. 371.
+  CARDAN, on a variety of the walnut, i. 356;
+    on grafted walnuts, ii. 259-260.
+  CARDOON, ii. 34.
+  _Carex rigida_, local sterility of the, ii. 170.
+  CARLIER, early selection of sheep, ii. 204.
+  CARLISLE, Sir A., inheritance of peculiarities, ii. 6, 8;
+    of polydactylism, ii. 13.
+  "CARME" pigeon, i. 156.
+  CARNATION, bud-variation in, i. 381;
+    variability of, i. 370;
+    striped, produced by crossing red and white, i. 393;
+    effect of conditions of life on the, ii. 273.
+  CARNIVORA, general fertility of, in captivity, ii. 150.
+  CAROLINE Archipelago, cats of, i. 47.
+  CARP, ii. 236.
+  CARPELS, variation of, in cultivated cucurbitaceae, i. 359.
+  CARPENTER, W. B., regeneration of bone, ii. 294;
+    production of double monsters, ii. 340;
+    number of eggs in an _Ascaris_, ii. 379.
+  _Carpinus betulus_, i. 362.
+  _Carpophaga littoralis_ and _luctuosa_, i. 182.
+  CARRIER pigeon, i. 139-142;
+    English, i. 139-141;
+    figured, i. 140;
+    skull figured, i. 163;
+    history of the, i. 211;
+    Persian, i. 141;
+    Bussorah, _ibid._;
+    Bagadotten, skull figured, i. 163;
+    lower jaw figured, i. 165.
+  CARRIERE, cultivation of the wild carrot, i. 326;
+    intermediate form between the almond and the peach, i. 338;
+    glands of peach-leaves, i. 343;
+    bud-variation in the vine, i. 375;
+    grafts of _Aria vestita_ upon thorns, i. 387;
+    variability of hybrids of _Erythrina_, ii. 265.
+  CARROT, wild, effects of cultivation on the, i. 326;
+    reversion in the, ii. 31;
+    run wild, ii. 33;
+    increased fertility of cultivated, ii. 113;
+    experiments on the, ii. 277;
+    acclimatisation of the, in India, ii. 311.
+  _Carthamus_, abortion of the pappus in, ii. 316.
+  CARTIER, cultivation of native plants in Canada, i. 312.
+  CARYOPHYLLACEAE, frequency of contabescence in the, ii. 165.
+  CASPARY, bud-variation in the moss-rose, i. 380;
+    on the ovules and pollen of _Cytisus_, i. 388-389;
+    crossing of _Cytisus purpureus_ and _C. laburnum_, i. 389;
+    trifacial orange, i. 391;
+    differently-coloured flowers in the wild _Viola lutea,_ i. 408;
+    sterility of the horse-radish, ii. 170.
+  CASTELNAU, on Brazilian cattle, i. 88.
+  CASTRATION, assumption of female characters caused by, ii. 51-52.
+  _Casuarius bennettii_, ii. 156.
+  CAT, domestic, i. 43-48;
+    early domestication and probable origin of the, i. 43-44;
+    intercrossing of with wild species, i. 44-45;
+    variations of, i. 45-48;
+    feral, i. 47, ii. 33;
+    anomalous, i. 48;
+    polydactylism in, ii. 14;
+    black, indications of stripes in young, ii. 55;
+    tortoiseshell, ii. 73;
+    effects of crossing in, ii. 86;
+    fertility of, ii. 111;
+    difficulty of selection in, ii. 234, 236;
+    length of intestines in, ii. 302;
+    white with blue eyes, deafness of, ii. 329;
+    with tufted ears, ii. 350.
+  CATARACT, hereditary, ii. 9, 79.
+  CATERPILLARS, effect of changed food on, ii. 280.
+  CATLIN, G., colour of feral horses in North America, i. 61.
+  CATTLE, European, their probable origin from three original species, i.
+      79-82;
+    humped, or Zebus, i. 79-80;
+    intercrossing of, i. 83, 91-93;
+    wild, of Chillingham, Hamilton, Chartley, Burton Constable, and
+        Gisburne, i. 84, ii. 119;
+    colour of feral, i. 84-85, ii. 102;
+    British breeds of, i. 86-87;
+    South African breeds of, i. 88;
+    South American breeds of, i. 89, ii. 205;
+    Niata, i. 89-91, ii. 205, 208, 332;
+    effects of food and climate on, i. 91-92;
+    effects of selection on, i. 92-93;
+    Dutch-buttocked, ii. 8;
+    hornless, production of horns in, ii. 29-30, 39;
+    reversion in, when crossed, ii. 41;
+    wildness of hybrid, ii. 45;
+    short-horned, prepotency of, ii. 65;
+    wild, influence of crossing and segregation on, ii. 86;
+    crosses of, ii. 96, 104, 118;
+    of Falkland islands, ii. 102;
+    mutual fertility of all varieties of, ii. 110;
+    effects of interbreeding on, ii. 117-119;
+    effects of careful selection on, ii. 194, 199;
+    naked, of Columbia, ii. 205;
+    crossed with wild banteng in Java, ii. 206;
+    with reversed hair in Banda Oriental, ii. 205;
+    selection of trifling characters in, ii. 209;
+    fashion in, ii. 210;
+    similarity of best races of, ii. 241;
+    unconscious selection in, ii. 214;
+    effects of natural selection on anomalous breeds of, ii. 226-227;
+    light-coloured, attacked by flies, ii. 229, 336;
+    Jersey, rapid improvement of, ii. 234;
+    effects of disuse of parts in, ii. 299;
+    rudimentary horns in, ii. 315;
+    supposed influence of humidity on the hair of, ii. 326;
+  {442}
+    white spots of, liable to disease, ii. 337;
+    supposed analogous variation in, ii. 349;
+    displacement of long-horned by short-horned, ii. 426.
+  CAULIFLOWER, i. 323;
+    free-seeding of, in India, ii. 310;
+    rudimentary flowers in, ii. 316.
+  CAVALIER pigeon, ii. 97.
+  _Cavia aperea_, ii. 152.
+  CAY (_Cebus azarae_), sterility of, in confinement, ii. 153.
+  _Cebus azarae_, ii. 153.
+  _Cecidomyia_, larval development of, ii. 283, 360, 367;
+    and _Misocampus_, i. 5.
+  CEDARS of Lebanon and Atlas, i. 364.
+  CELERY, turnip-rooted, i. 336;
+    run wild, ii. 33.
+  CELL-THEORY, ii. 370.
+  _Celosia cristata_, i. 365.
+  CELSUS, on the selection of seed-corn, i. 318, ii. 203.
+  CELTS, early cultivation of the cabbage by the, i. 324;
+    selection of cattle and horses by the, ii. 202-203.
+  _Cenchrus_, seeds of a, used as food, i. 309.
+  _Centaurea cyanus_, bud-variation in, i. 379.
+  CEPHALOPODA, spermatophores of, ii. 383.
+  _Cerasus padus_, yellow-fruited, ii. 19.
+  _Cercoleptes_, sterility of, in captivity, ii. 152.
+  _Cercopithecus_, breeding of a species of, in captivity, ii. 153.
+  CEREALS, i. 312-313;
+    of the Neolithic period in Switzerland, i. 317;
+    adaptation of, to soils, ii. 305.
+  _Cereus_, ii. 38.
+  _Cereus speciosissimus_ and _phyllanthus_, reversion in hybrids of, i.
+      392.
+  _Cervus canadensis_, ii. 158.
+  _Cervus dama_, ii. 120.
+  CETACEA, correlation of dermal system and teeth in the, ii. 328.
+  CEYLON, cats of, i. 46;
+    pigeon-fancying in, i. 206.
+  _Chamaerops humilis_, crossed with date palm, i. 399.
+  CHAMISSO, on seeding bread-fruit, ii. 168.
+  CHANNEL islands, breeds of cattle in, i. 80.
+  CHAPMAN, Professor, peach-trees producing nectarines, i. 341.
+  CHAPUIS, F., sexual peculiarities in pigeons, i. 162, ii. 74;
+    effect produced by first male upon the subsequent progeny of the
+        female, i. 405;
+    sterility of the union of some pigeons, ii. 162.
+  CHARACTERS, fixity of, ii. 239;
+    latent, ii. 51-56, 399-400;
+    continued divergence of, ii. 241;
+    antagonistic, ii. 401.
+  CHARDIN, abundance of pigeons in Persia, i. 205.
+  CHARLEMAGNE, orders as to the selection of stallions, ii. 203.
+  CHARTLEY, wild cattle of, i. 84.
+  CHATE, reversion of the upper seeds in the pods of stocks, ii. 347-348.
+  CHATIN, on _Ranunculus ficaria_, ii. 170.
+  CHAUNDY, Mr., crossed varieties of cabbage, ii. 130.
+  CHEETAH, general sterility of, in captivity, ii. 151.
+  _Cheiranthus cheiri_, i. 382.
+  CHERRIES, i. 347-348;
+    bud-variation in, i. 375;
+    white Tartarian, ii. 230;
+    variety of, with curled petals, ii. 232;
+    period of vegetation of, changed by forcing, ii. 311.
+  CHEVREUL, on crossing fruit-trees, ii. 129.
+  CHICKENS, differences in characters of, i. 249-250;
+    white, liable to gapes, ii. 228, 336.
+  CHIGOE, ii. 275.
+  CHILE, sheep of, i. 95.
+  CHILLINGHAM cattle, identical with _Bos primigenius_, i. 81;
+    characters of, i. 83-84.
+  CHILOE, half-castes of, ii. 46.
+  CHINA, cats of, with drooping ears, i. 47;
+    horses of, i. 53;
+    striped ponies of, i. 59;
+    asses of, i. 62;
+    notice of rabbits in, by Confucius, i. 103;
+    breeds of pigeons reared in, i. 206;
+    breeds of fowls of, in fifteenth century, i. 232, 247;
+    goose of, i. 237.
+  CHINCHILLA, fertility of, in captivity, ii. 152.
+  CHINESE, selection practised by the, ii. 204-205;
+    preference of the, for hornless rams, ii. 209;
+    recognition of the value of native breeds by the, ii. 313.
+  CHINESE, or Himalayan rabbit, i. 108.
+  "CHIVOS," a breed of cattle in Paraguay, i. 89.
+  CHOUX-RAVES, i. 323.
+  CHRIST, H., on the plants of the Swiss Lake-dwellings, i. 309, 318;
+    intermediate forms between _Pinus sylvestris_ and _montana_, i. 363.
+  CHRYSANTHEMUM, i. 379.
+  _Chrysotis festiva_, ii. 280.
+  CINERARIA, effects of selection on the, ii. 200.
+  CIRCASSIA, horses of, ii. 102.
+  CIRCUMCISION, ii. 23.
+  CIRRIPEDES, metagenesis in, ii. 366.
+  _Cistus_, intercrossing and hybrids of, i. 336, 389, ii. 140.
+  _Cistus tricuspis_, bud-variation in, i. 377.
+  CITRONS, i. 334-335.
+  "_Citrus aurantium fructu variabili_," i. 336.
+  _Citrus decumana_, i. 335.
+  _Citrus lemonum_, i. 336.
+  {443}
+  _Citrus medica_, i. 335-336.
+  CLEFT palate, inheritance of, ii. 24.
+  CLEMENTE, on wild vines in Spain, i. 332.
+  CLERMONT-TONNERRE, on the St. Valery apple, i. 401.
+  CLAPHAM, A., bud-variation in the hawthorn, i. 377.
+  "CLAQUANT," i. 138.
+  "CLAQUERS" (pigeons), i. 156.
+  CLARK, G., on the wild dogs of Juan de Nova, i. 27;
+    on striped Burmese and Javanese ponies, i. 59;
+    breeds of goats imported into the Mauritius, i. 101;
+    variations in the mammae of goats, i. 102;
+    bilobed scrotum of Muscat goat, _ibid._
+  CLARK, H. J., on fission and gemmation, ii. 359.
+  CLARKE, R. T., intercrossing of strawberries, i. 352.
+  CLARKE, T., hybridisation of stocks, i. 399, ii. 93.
+  CLARKSON, Mr., prize-cultivation of the gooseberry, i. 355.
+  CLASSIFICATION, explained by the theory of natural selection, i. 11.
+  CLIMATE, effect of, upon breeds of dogs, i. 37;
+    on horses, i. 52, 53;
+    on cattle, i. 91, 92;
+    on the fleece of sheep, i. 98, 99;
+    on seeds of wheat, i. 316;
+    on cultivated cabbages, i. 325;
+    adaptation of maize to, i. 322.
+  CLIMATE and pasture, adaptation of breeds of sheep to, i. 96-97.
+  CLIMATE and soil, effects of, upon strawberries, i. 353.
+  CLINE, Mr., on the skull in horned and hornless rams, ii. 333.
+  CLOS, on sterility in _Ranunculus ficaria_, ii. 170.
+  CLOTZSCH, hybrids of various trees, ii. 130.
+  CLOVER, pelorism in, ii. 340.
+  COATE, Mr., on interbreeding pigs, ii. 122.
+  COCCUS of apple trees, ii. 231.
+  COCHIN fowls, i. 227, 250, 252, 260-261;
+    occipital foramen of, figured, i. 261;
+    section of skull of, figured, i. 263;
+    cervical vertebra of, figured, i. 267.
+  COCHINEAL, persistence of, ii. 236;
+    preference of, for a particular cactus, ii. 275.
+  _Cochlearia armoracia_, ii. 170.
+  COCK, game, natural selection in, ii. 225;
+    spur of, grafted on the comb, ii. 296;
+    spur of, inserted into the eye of an ox, ii. 369;
+    effect of castration upon the, ii. 51-52.
+  COCK'S-COMB, varieties of the, i. 365.
+  COCOONS, of silkworms, variations in, i. 302-303.
+  CODFISH, bulldog, i. 89;
+    number of eggs in the, ii. 379.
+  _Coelogenys paca_, ii. 152.
+  COLIN, prepotency of the ass over the horse, ii. 67-68;
+    on cross-breeding, ii. 97;
+    on change of diet, ii. 304.
+  COLLINSON, Peter, peach-tree producing a nectarine, i. 340.
+  COLORATION, in pigeons, an evidence of unity of descent, i. 195-197.
+  COLOUR, correlation of, in dogs, i. 28-29;
+    persistence of, in horses, i. 50;
+    inheritance and diversity of, in horses, i. 55;
+    variations of, in the ass, i. 62-63;
+    of wild or feral cattle, i. 85;
+    transmission of, in rabbits, i. 107;
+    peculiarities of, in Himalayan rabbits, i. 111;
+    influence of, ii. 227-230;
+    correlation of, in head and limbs, ii. 324;
+    correlated with constitutional peculiarities, ii. 335-338.
+  COLOUR and odour, correlation of, ii. 325.
+  COLOUR-BLINDNESS, hereditary, ii. 9;
+    more common in men than in women, ii. 72-73;
+    associated with inability to distinguish musical sounds, ii. 328.
+  COLOURS, sometimes not blended by crossing, ii. 92.
+  _Columba affinis_, Blyth, a variety of _C. livia_, i. 183.
+  _Columba amaliae_, Brehm, a variety of _C. livia_, i. 183.
+  _Columba guinea_, i. 182.
+  _Columba gymnocyclus_, Gray, a form of _C. livia_, i. 184.
+  _Columba gymnophthalmos_, hybrids of, with _C. oenas_, i. 193;
+    with _C. maculosa_, i. 194.
+  _Columba intermedia_, Strickland, a variety of _C. livia_, i. 184.
+  _Columba leucocephala_, ii. 155.
+  _Columba leuconota_, i. 182, 195.
+  _Columba littoralis_, i. 182.
+  _Columba livia_, ii. 29, 40;
+    the parent of domestic breeds of pigeons, i. 183;
+    measurements of, i. 134;
+    figured, i. 135;
+    skull figured, i. 163;
+    lower jaw figured, i. 164, 168;
+    scapula figured, i. 167.
+  _Columba luctuosa_, i. 182.
+  _Columba migratoria_ and _leucocephala_, diminished fertility of, in
+      captivity, ii. 155.
+  _Columba oenas_, i. 183;
+    crossed with common pigeon and _C. gymnophthalmos_, i. 193.
+  _Columba palumbus_, i. 193, ii. 350.
+  _Columba rupestris_, i. 182, 184, 195.
+  _Columba Schimperi_, i. 184.
+  _Columba torquatrix_, ii. 350.
+  _Columba turricola_, i. 184.
+  COLUMBIA, cattle of, i. 88.
+  COLUMBINE, double, i. 365, ii. 330.
+  {444}
+  COLUMBUS, on West Indian dogs, i. 23.
+  COLUMELLA, on Italian shepherd's dogs, i. 23;
+    on domestic fowls, i. 231,  247, ii. 202, 429;
+    on the keeping of ducks, i. 277;
+    on the selection of seed-corn, i. 318;
+    on the benefits of change of soil to plants, ii. 146;
+    on the value of native breeds, ii. 313.
+  COLZA, i. 325.
+  COMB, in fowls, variations of, i. 253-254;
+    sometimes rudimentary, ii. 315.
+  COMPENSATION, law of, i. 274.
+  COMPENSATION of growth, ii. 342-344.
+  COMPLEXION, connexion of, with constitution, ii. 335.
+  COMPOSITAE, double flowers of, i. 365, ii. 167, 316.
+  CONCEPTION, earlier in Alderney and Zetland cows than in other breeds, i.
+      87.
+  CONDITIONS of life, changed, effect of, ii. 418-419;
+    on horses, i. 52;
+    upon variation in pigeons, i. 212-213;
+    upon wheat, i. 315-316;
+    upon trees, i. 361;
+    in producing bud-variation, i. 408;
+    advantages of, ii. 145-148, 176-177;
+    sterility caused by, ii. 148-165;
+    conducive to variability, ii. 255-261, 394;
+    accumulative action of, ii. 261-263;
+    direct action of, ii. 271-292.
+  CONDOR, breeding in captivity, ii. 154.
+  CONFINEMENT, effect of, upon the cock, ii. 52.
+  CONFUCIUS, on the breeding of rabbits in China, i. 103.
+  CONOLLY, Mr., on Angora goats, ii. 326.
+  CONSTITUTIONAL differences in sheep, i. 96-97;
+    in varieties of apples, i. 349-350;
+    in pelargoniums, i. 364;
+    in dahlias, i. 370.
+  CONSTITUTIONAL peculiarities in strawberries, i. 353;
+    in roses, i. 367.
+  CONSUMPTION, hereditary, ii. 8;
+    period of appearance of, ii. 77;
+    correlated with complexion, ii. 335.
+  CONTABESCENCE, ii. 165-166.
+  _Convolvulus batatas_, ii. 169, 309.
+  _Convolvulus tricolor_, bud-variation in, i. 408.
+  COOPER, Mr., improvement of vegetables by selection, ii. 204.
+  COOPER, White, hereditary peculiarities of vision, ii. 9;
+    association of affections of the eyes with those of other systems, ii.
+        328.
+  CORALS, bud-variation in, i. 374;
+    non-diffusion of cell-gemmules in, ii. 379.
+  CORBIE. _See_ Boitard.
+  CORNEA, opacity of, inherited, ii. 9.
+  _Cornus mascula_, yellow-fruited, ii. 19.
+  CORRELATION, ii. 319;
+    of neighbouring parts, ii. 320;
+    of change in the whole body and in some of its parts, ii. 321;
+    of homologous parts, ii. 322-331;
+    inexplicable, ii. 331-333;
+    commingling of, with the effects of other agencies, ii. 333-335.
+  CORRELATION of skull and limbs in swine, i. 73;
+    of tusks and bristles in swine, i. 76;
+    of multiplicity of horns and coarseness of wool in sheep, i. 95;
+    of beak and feet in pigeons, i. 172-173;
+    between nestling down and colour of plumage in pigeons, i. 194;
+    of changes in silkworms, i. 304;
+    in plants, ii. 219;
+    in maize, i. 323;
+    in pigeons, i. 167-171, 218;
+    in fowls, i. 274-275.
+  CORRESPONDING periods, inheritance at, ii. 75-80.
+  CORRIENTES, dwarf cattle of, i. 89.
+  CORRINGHAM, Mr., influence of selection on pigs, ii. 198.
+  CORSICA, ponies of, i. 52.
+  "CORTBECK" (pigeon) of Aldrovandi, i. 209.
+  _Corvus corone_ and _C. cornix_, hybrids of, ii. 94.
+  _Corydalis_, flower of, ii. 304.
+  _Corydalis cava_, ii. 132-133.
+  _Corydalis solida_, sterile when peloric, ii. 167.
+  _Corydalis tuberosa_, peloric by reversion, ii. 58-59.
+  _Corylus avellana_, i. 357.
+  COSTA, A., on shells transferred from England to the Mediterranean, ii.
+      280.
+  "COUVE TRONCHUDA," i. 323.
+  COW, inheritance of loss of one horn in the, ii. 12, 23;
+    amount of milk furnished by the, ii. 300;
+    development of six mammae in, ii. 317.
+  COWSLIP, ii. 21, 182.
+  CRACIDAE, sterility of the, in captivity, ii. 156.
+  CRANES, fertility of, in captivity, ii. 156.
+  _Crataegus oxyacantha_, i. 363, ii. 18, 232, 258, 377.
+  _Crataegus monogyna_, i. 364.
+  _Crataegus sibirica_, i. 364.
+  CRAWFURD, J., Malasian cats, i. 47;
+    horses of the Malay Archipelago, i. 49;
+    horses of Japan, i. 53;
+    occurrence of stripes in young wild pigs of Malacca, i. 76;
+    on a Burmese hairy family with deficient teeth, ii. 77, 327;
+    Japanese origin of the bantam, i. 230;
+    game fowls of the Philippine islands, i. 232;
+    hybrids of _Gallus varius_ and domestic fowl, i. 234;
+    domestication of _Gallus bankiva_, i. 236;
+    feral fowls in the Pellew islands, i. 238;
+    history of the fowl, i. 246;
+    history of the domestic duck, i. 277;
+    domestication of the goose, i. 287;
+    cultivated plants of New Zealand, i. 312;
+  {445}
+    breeding of tame elephants in Ava, ii. 150;
+    sterility of _Goura coronata_ in confinement, ii. 155;
+    geese of the Philippine islands, ii. 162.
+  CREEPERS, a breed of fowls, i. 230.
+  CRESTED fowl, i. 227;
+    figured, i. 229.
+  "CREVE-COEUR," a French sub-breed of fowls, i. 229.
+  CRISP, Dr., on the brains of the hare and rabbit, i. 126.
+  CROCKER, C. W., singular form of _Begonia frigida_, i. 365-366, ii. 166;
+    sterility in _Ranunculus ficaria_, ii. 170.
+  CROCUS, ii. 165.
+  CROSS-BREEDING, permanent effect of, on the female, i. 404.
+  CROSSING, ii. 85-144, 173-192;
+    a cause of uniformity, ii. 85-90, 173;
+    occurs in all organised beings, ii. 90-92;
+    some characters not blended by, ii. 92-95, 173;
+    modifications and new races produced by, ii. 95-99;
+    causes which check, ii. 100-109;
+    domestication and cultivation favourable to, ii. 109-113, 189;
+    beneficial effects of, ii. 114-131, 174-176;
+    necessary in some plants, ii. 131-140, 175-176, 423;
+    summary of subject of, ii. 140-144;
+    of dogs with wolves in North America, i. 21-22;
+    with _Canis cancrivorus_ in Guiana, i. 23;
+    of dog with wolf, described by Pliny and others, i. 24;
+    characters furnished by, brought out by reversion in the progeny, ii.
+        34-36;
+    a direct cause of reversion, ii. 39-47, 48;
+    a cause of variability, ii. 264-267.
+  CRUSTACEA, macrourous, differences in the development of the, ii. 368.
+  CRUSTACEAN with an antenna-like development of the eye-peduncle, ii. 391.
+  CRYPTOGAMIC plants, bud-variation in, i. 383.
+  CUBA, wild dogs of, i. 27.
+  "CUCKOO," sub-breeds of fowls, i. 244.
+  CUCUMBER, variation in number of carpels of, i. 359;
+    supposed crossing of varieties of the, i. 400.
+  _Cucumis momordica_, i. 360.
+  _Cucumis sativa_, i. 359.
+  _Cucurbita_, dwarf, correlation of leaves in, ii. 330.
+  _Cucurbita maxima_, i. 357, 359.
+  _Cucurbita moschata_, i. 357, 359.
+  _Cucurbita pepo_, i. 357, ii. 108;
+    varieties of, i. 358;
+    relation in size and number of fruit of, ii. 343.
+  CUCURBITACEAE, i. 357-360;
+    supposed crossing of, i. 399;
+    Naudin's observations on hybrids of, ii. 172;
+    acclimatisation of, ii. 313.
+  "CULBUTANTS" (pigeons), i. 150.
+  CULTIVATION of plants, origin of, among savages, i. 309-310;
+    fertility increased by, ii. 111-113.
+  CUNIER, on hereditary night-blindness, ii. 9.
+  CURRANTS, of Tierra del Fuego, i. 309;
+    bud-variation in, i. 376.
+  CURTIS, Mr., bud-variation in the rose, i. 381.
+  CUVIER, on the gestation of the wolf, i. 29;
+    the odour of the jackal, an obstacle to domestication, i. 30;
+    differences of the skull in dogs, i. 34;
+    external characters of dogs, i. 35;
+    elongation of the intestines in domestic pigs, i. 73, ii. 303;
+    fertility of the hook-billed duck, i. 277;
+    number of digits, ii. 13;
+    hybrid of ass and zebra, ii. 42;
+    breeding of animals in the Jardin des Plantes, ii. 149;
+    sterility of predaceous birds in captivity, ii. 154;
+    facility of hybridisation in confinement, ii. 160.
+  CYANOSIS, affection of fingers in, ii. 332.
+  CYCLAMEN, bud-variation in, i. 382.
+  _Cynara cardunculus_, ii. 34.
+  _Cynips fecundatrix_, ii. 283.
+  _Cynocephalus hamadryas_, ii. 153.
+  _Cyprinus auratus_, i. 296-297.
+  _Cyrtanthus_, ii. 139.
+  _Cyrtopodium_, ii. 134.
+  _Cytisus Adami_, ii. 364;
+    its bud-variation, i. 387-389, 406, ii. 37;
+    seedlings from, i. 388;
+    different views of its origin, i. 389-390;
+    experiments in crossing _C. purpureus_ and _laburnum_ to produce, i.
+        389;
+    its production by M. Adam, i. 390;
+    discussion of origin of, i. 396.
+  _Cytisus alpino-laburnum_, ovules and pollen of, i. 389;
+    origin of, i. 390.
+  _Cytisus alpinus_, i. 388.
+  _Cytisus laburnum_, i. 387, 389, 390, 396.
+  _Cytisus purpureo-elongatus_, ovules and pollen of, i. 389;
+    production of, i. 390.
+  _Cytisus purpureus_, i. 387, 388, 389, 390, 396.
+
+  DAHLBOM, effects of food on hymenoptera, ii. 281.
+  DAHLIA, i. 369-370, ii. 147;
+    bud-variation by tubers in the, i. 385;
+    improvement of, by selection, ii. 216;
+    steps in cultivation of, ii. 261;
+    effect of conditions of life on, ii. 273;
+    correlation of form and colour in, ii. 331.
+  DAISY, hen and chicken, i. 365;
+    Swan River, ii. 261.
+  DALBRET, varieties of wheat, i. 314.
+  DALIBERT, changes in the odours of plants, ii. 274.
+  DALLY, Dr., on consanguineous marriages, ii. 122.
+  DALTONISM, hereditary, ii. 9.
+  DAMARAS, cattle of, i. 88, ii. 207-208.
+  {446}
+  DAMSON, i. 347.
+  DANDOLO, Count, on silkworms, i. 301.
+  DANIELL, fertility of English dogs in Sierra Leone, ii. 161.
+  DANISH Middens, remains of dogs in, i. 18.
+  DAPPLING in horses, asses, and hybrids, i. 55.
+  DARESTE. C., on the skull of the Polish fowl, i. 262;
+    on the production of monstrous chickens, ii. 289;
+    co-existence of anomalies, ii. 331;
+    production of double monsters, ii. 340.
+  DARVILL, Mr., heredity of good qualities in horses, ii. 11.
+  DARWIN, C., on _Lepus magellanicus_, i. 112;
+    on the wild potato, i. 330;
+    dimorphism in the polyanthus and primrose, ii. 21.
+  DARWIN, Dr., improvement of vegetables by selection, ii. 204.
+  DARWIN, Sir F., wildness of crossed pigs, ii. 45.
+  D'ASSO, monogynous condition of the hawthorn in Spain, i. 364.
+  _Dasyprocta aguti_, ii. 152.
+  Date-palm, varieties of the, ii. 256;
+    effect of pollen of, upon the fruit of _Chamaerops_, i. 299.
+  _Datura_, ii. 38;
+    variability in, ii. 266.
+  _Datura laevis_ and _stramonium_, reversion in hybrids of, i. 392.
+  _Datura stramonium_, ii. 67.
+  DAUBENTON, variations in the number of mammae in dogs, i. 35;
+    proportions of intestines in wild and domestic cats, i. 48, ii. 302.
+  DAUDIN, on white rabbits, ii. 230.
+  DAVY, Dr., on sheep in the West Indies, i. 98.
+  DAWKINS and Sandford, early domestication of _Bos longifrons_ in Britain,
+      i. 81.
+  DEAF-MUTES, non-heredity of, ii. 22.
+  DEAFNESS, inheritance of, ii. 78.
+  DEBY, wild hybrids of common and musk ducks, ii. 46.
+  DE CANDOLLE, Alph., number and origin of cultivated plants, i. 306-307,
+      371;
+    regions which have furnished no useful plants, i. 310;
+    wild wheat, i. 312-313;
+    wild rye and oats, i. 313;
+    antiquity of varieties of wheat, i. 316;
+    apparent inefficacy of selection in wheat, i. 318;
+    origin and cultivation of maize, i. 320, ii. 307;
+    colours of seeds of maize, i. 321;
+    varieties and origin of the cabbage, i. 324-325;
+    origin of the garden-pea, i. 326;
+    on the vine, i. 332, ii. 308;
+    cultivated species of the orange group, i. 335;
+    probable Chinese origin of the peach, i. 337;
+    on the peach and nectarine, i. 340, 342;
+    varieties of the peach, i. 342;
+    origin of the apricot, i. 344;
+    origin and varieties of the plum, i. 345;
+    origin of the cherry, i. 347;
+    varieties of the gooseberry, i. 354;
+    selection practised with forest-trees, i. 361;
+    wild fastigate oak, i. 361;
+    dark-leaved varieties of trees, i. 362;
+    conversion of stamens into pistils in the poppy, i. 365;
+    variegated foliage, i. 366;
+    heredity of white hyacinths, i. 371, ii. 20;
+    changes in oaks dependent on age, i. 387;
+    inheritance of anomalous characters, ii. 19;
+    variation of plants in their native countries, ii. 256;
+    deciduous bushes becoming evergreen in hot climates, ii. 305;
+    antiquity of races of plants, ii. 429.
+  DE CANDOLLE, P., non-variability of monotypic genera, ii. 266;
+    relative development of root and seed in _Raphanus sativus_, ii. 343.
+  DECAISNE, on the cultivation of the wild carrot, i. 326;
+    varieties of the pear, i. 350;
+    inter-crossing of strawberries, i. 351;
+    fruit of the apple, i. 401;
+    sterility of _Lysimachia nummularia_, ii. 170;
+    tender variety of the peach, ii. 308.
+  DEER, assumption of horns by female, ii. 51;
+    imperfect development of horns in a, on a voyage, ii. 158.
+  DEER, fallow, ii. 103.
+  DEERHOUND. Scotch, difference in size of the sexes of, ii. 73;
+    deterioration of, ii. 121.
+  DEGENERATION of high-bred races, under neglect, ii. 239.
+  DE JONGHE, J., on strawberries, i. 352, ii. 243;
+    soft-barked pears, ii. 231;
+    on accumulative variation, ii. 262;
+    resistance of blossoms to frost, ii. 306.
+  DELAMER, E. S., on rabbits, i. 107, 112.
+  _Delphinium ajacis_, ii. 21.
+  _Delphinium consolida_, ii. 20-21.
+  _Dendrocygna viduata_, i. 182, ii. 157.
+  DENTITION, variations of, in the horse, i. 50.
+  DEODAR, i. 364.
+  DESMAREST, distribution of white on dogs, i. 29;
+    cat from the Cape of Good Hope, i. 47;
+    cats of Madagascar, i. 47;
+    occurrence of striped young in Turkish pigs, i. 76;
+    French breeds of cattle, i. 80;
+    horns of goats, i. 102;
+    on hornless goats, ii. 315.
+  DESOR, E., on the Anglo-Saxon race in America, ii. 276.
+  DESPORTES, number of varieties of roses, i. 367.
+  DEVAY, Dr., singular case of albinism, ii. 17;
+    on the marriage of cousins, ii. 122;
+    on the effects of close interbreeding, ii. 143, 263.
+  DEVELOPMENT and metamorphosis, ii. 388-389.
+  DEVELOPMENT, arrests of, ii. 315-318.
+  DEVELOPMENT, embryonic, ii. 366-368.
+  {447}
+  D'HERVEY-Saint-Denys, L., on the ya-mi, or imperial rice of the Chinese,
+      ii. 205.
+  DHOLE, fertility of the, in captivity, ii. 151.
+  DIABETES, occurrence of, in three brothers, ii. 17.
+  _Dianthus_, contabescent plants of, ii. 165-166;
+    hybrid varieties of, ii. 267.
+  _Dianthus armeria_ and _deltoides_, hybrids of, ii. 98.
+  _Dianthus barbatus_, i. 381.
+  _Dianthus caryophyllus_, i. 381.
+  _Dianthus japonicus_, contabescence of female organs in, ii. 166.
+  DICHOGAMOUS plants, ii. 90.
+  DICKSON, Mr., on "running" in carnations, i. 381;
+    on the colours of tulips, i. 386.
+  _Dicotyles torquatus_ and _labiatus_, ii. 150.
+  DIEFFENBACH, dog of New Zealand, i. 26;
+    feral cats in New Zealand, i. 47;
+    polydactylism in Polynesia, ii. 14.
+  _Dielytra_, ii. 59.
+  DIET, change of, ii. 303-304.
+  _Digitalis_, properties of, affected by culture, ii. 274;
+    poison of, ii. 380.
+  DIGITS, supernumerary, ii. 57;
+    analogy of, with embryonic conditions, ii. 16;
+    fusion of, ii. 341.
+  DIMORPHIC plants, ii. 166;
+    conditions of reproduction in, ii. 181-184.
+  DIMORPHISM, reciprocal, ii. 90.
+  DINGO, i. 25;
+    variation of, in colour, i. 28;
+    half-bred, attempting to burrow, i. 28;
+    attraction of foxes by a female, i. 31;
+    variations of, in confinement, ii. 263.
+  DIOECIOUSNESS of strawberries, i. 353.
+  DISEASES, inheritance of, ii. 7-8;
+    family uniformity of, ii. 57;
+    inherited at corresponding periods of life, ii. 77-80;
+    peculiar to localities and climates, ii. 276;
+    obscure correlations in, ii. 331-332;
+    affecting certain parts of the body, ii. 380;
+    occurring in alternate generations, ii. 401.
+  DISTEMPER, fatal to white terriers, ii. 227.
+  DISUSE and use of parts, effects of, ii. 295-303, 352-353, 418-419;
+    in the skeleton of rabbits, i. 124-128;
+    in pigeons, i. 171-177;
+    in fowls, i. 270-274;
+    in ducks, i. 284-286;
+    in the silk-moth, i. 300-304.
+  DIVERGENCE, influence of, in producing breeds of pigeons, i. 220.
+  DIXON, E. S., on the musk duck, i. 182;
+    on feral ducks, i. 190;
+    on feral pigeons in Norfolk Island, i. 190;
+    crossing of pigeons, i. 192;
+    origin of domestic fowls, i. 230;
+    crossing of _Gallus Sonneratii_ and common fowl, i. 234;
+    occurrence of white in the young chicks of black fowls, i. 244;
+    Paduan fowl of Aldrovandi, i. 247;
+    peculiarities of the eggs of fowls, i. 248;
+    chickens, i. 249-250;
+    late development of the tail in Cochin cocks, i. 250;
+    comb of lark-crested fowls, i. 256;
+    development of webs in Polish fowls, i. 259;
+    on the voice of fowls, i. 259;
+    origin of the duck, i. 277;
+    ducks kept by the Romans, i. 278;
+    domestication of the goose, i. 287;
+    gander frequently white, i. 288;
+    breeds of turkeys, i. 293;
+    incubatory instinct of mongrels of non-sitting races of fowls, ii. 44;
+    aversion of the dove-cot pigeon to pair with fancy birds, ii. 103;
+    fertility of the goose, ii. 112;
+    general sterility of the guans in captivity, ii. 156;
+    fertility of geese in captivity, ii. 157;
+    white peafowl, ii. 332.
+  DOBELL, H., inheritance of anomalies of the extremities, ii. 14;
+    non-reversion to a malformation, ii. 36.
+  DOBRIZHOFFER, abhorrence of incest by the Abipones, ii. 123.
+  DOGS, origin of, i. 15;
+    ancient breeds of, i. 17, ii. 429;
+    of neolithic, bronze and iron periods in Europe, i. 18-19, ii. 427;
+    resemblance of to various species of canidae, i. 21;
+    of North America compared with wolves, i. 21-22;
+    of the West Indies, South America, and Mexico, i. 23, 31;
+    of Guiana, i. 23;
+    naked dogs of Paraguay and Peru, _ibid._ and 31;
+    dumb, on Juan Fernandez, i. 27;
+    of Juan de Nova, i. 27;
+    of La Plata, i. 27;
+    of Cuba, i. 27;
+    of St. Domingo, i. 28;
+    correlation of colour in, i. 28-29;
+    gestation of, i. 29-30;
+    hairless Turkish, i. 30, ii. 227;
+    inter-crossing of different breeds of, i. 31;
+    characters of different breeds of, discussed, i. 34-37;
+    degeneration of European, in warm climates, i. 36, 38; ii. 278, 305;
+    liability to certain diseases in different breeds of, i. 36 and _note_;
+    causes of differences of breeds discussed, i. 37-43;
+    catching fish and crabs in New Guinea and Tierra del Fuego, i. 39;
+    webbing of the feet in, i. 39;
+    influence of selection in producing different breeds of, i. 39, 43;
+    retention of original habits by, i. 182;
+    inheritance of polydactylism in, ii. 14;
+    feral, ii. 33;
+    reversion in fourth generation of, ii. 34;
+    of the Pacific Islands, ii. 87, 220, 303;
+    mongrel, ii. 92-93;
+    comparative facility of crossing different breeds of, ii. 102;
+    fertility of, ii. 111, 151;
+    inter-breeding of, ii. 120-121;
+    selection of, among the Greeks, ii. 202, 209;
+    among savages, ii. 206-207;
+    unconscious selection of, ii. 211-212;
+    valued by the Fuegians, ii. 215;
+    climatal changes in hair of, ii. 278;
+    production of drooping ears in, ii. 301;
+  {448}
+    rejection of bones of game by, ii. 303;
+    inheritance of rudiments of limbs in, ii. 315;
+    development of fifth toe in, ii. 317;
+    hairless, deficiency of teeth in, ii. 326;
+    short-faced, teeth of, ii. 345;
+    probable analogous variation in, ii. 349;
+    extinction of breeds of, ii. 425.
+  DOMBRAIN, H. H., on the auricula, ii. 346-347.
+  DOMESTICATION, essential points in, ii. 405-406;
+    favourable to crossing, ii. 109-110;
+    fertility increased by, ii. 111-113, 174.
+  DOMESTICATED animals, origin of, ii. 160-161;
+    occasional sterility of, under changed conditions, ii. 161-162.
+  DONDERS, Dr., hereditary hypermetropia, ii. 8.
+  DORKING fowl, i. 227, 261;
+    furcula of, figured, i. 268.
+  DORMOUSE, ii. 152.
+  DOUBLE FLOWERS, ii. 167-168, 171-172;
+    produced by selection, ii. 200.
+  DOUBLEDAY, H., cultivation of the filbert pine strawberry, i. 354.
+  DOUGLAS, J., crossing of white and black game-fowls, ii. 92.
+  DOWNING, Mr., wild varieties of the hickory, i. 310;
+    peaches and nectarines from seed, i. 339-340;
+    origin of the Boston nectarine, i. 340;
+    American varieties of the peach, i. 343;
+    North American apricot, i. 344;
+    varieties of the plum, i. 346;
+    origin and varieties of the cherry, i. 347-348;
+    "twin cluster pippins," i. 349;
+    varieties of the apple, i. 350;
+    on strawberries, i. 351, 353;
+    fruit of the wild gooseberry, i. 355;
+    effects of grafting upon the seed, ii. 26;
+    diseases of plum and peach trees, ii. 227-228;
+    injury done to stone fruit in America by the "weevil," ii. 231;
+    grafts of the plum and peach, ii. 259;
+    wild varieties of pears, ii. 260;
+    varieties of fruit-trees suitable to different climates, ii. 306.
+  _Draba sylvestris_, ii. 163.
+  DRAGON, pigeon, i. 139, 141.
+  "DRAIJER" (pigeon), i. 156.
+  DRINKING, effects of, in different climates, ii. 289.
+  DROMEDARY, selection of, ii. 205-206.
+  DRUCE, Mr., inter-breeding of pigs, ii. 121.
+  DU CHAILLU, fruit-trees in West Africa, i. 309.
+  DUCHESNE on _Fragaria vesca_, i. 351, 352, 353.
+  DUFOUR, Leon, on _Cecidomyia_ and _Misocampus_, i. 5.
+  DUCK, musk, retention of perching habit by the, i. 182;
+    feral hybrid of, i. 190.
+  DUCK, penguin, hybrid of, with Egyptian goose, ii. 68.
+  DUCK, wild, difficulty of rearing, ii. 233;
+    effects of domestication on, ii. 278.
+  DUCKS, breeds of, i. 276-277;
+    origin of, i. 277;
+    history of, _ibid._;
+    wild, easily tamed, i. 278-279;
+    fertility of breeds of, when crossed, i. 279;
+    with the plumage of _Anas boschas_, i. 280;
+    Malayan penguin, identical in plumage with English, i. 280;
+    characters of the breeds of, i. 281-284;
+    eggs of, i. 281;
+    effects of use and disuse in, i. 284-286, ii. 298;
+    feral, in Norfolk, i. 190;
+    Aylesbury, inheritance of early hatching by, ii. 25;
+    reversion in, produced by crossing, ii. 40;
+    wildness of half-bred wild, ii. 45;
+    hybrids of, with the musk duck, ii. 45-46;
+    assumption of male plumage by, ii. 51;
+    crossing of Labrador and penguin, ii. 97;
+    increased fertility of, by domestication, ii. 112;
+    general fertility of, in confinement, ii. 157;
+    increase of size of, by care in breeding, ii. 199;
+    change produced by domestication in, ii. 262.
+  DUMERIL, Aug., breeding of _Siredon_ in the branchiferous stage, ii. 384.
+  DUN-coloured horses, origin of, i. 59.
+  DUREAU de la Malle, feral pigs in Louisiana, ii. 33;
+    feral fowls in Africa, _ibid._;
+    bud-variation in the pear, i. 376;
+    production of mules among the Romans, ii. 110.
+  _Dusicyon sylvestris_, i. 23.
+  DUTCH rabbit, i. 107.
+  DUTCH roller pigeon, i. 151.
+  DUTROCHET, pelorism in the laburnum, ii. 346.
+  DUVAL, growth of pears in woods in France, ii. 260.
+  DUVAL-Jouve, on _Leersia oryzoides_, ii. 91.
+  DUVERNOY, self-impotence in _Lilium candidum_, ii. 137.
+  DZIERZON, variability in the characters and habits of bees, i. 298.
+
+  EARLE, Dr., on colour-blindness, ii. 72, 328.
+  EARS, of fancy rabbits, i. 106;
+    deficiency of, in breeds of rabbits, i. 108;
+    rudimentary, in Chinese sheep, ii. 315;
+    drooping, ii. 301;
+    fusion of, ii. 341.
+  EATON, J. M., on fancy pigeons, i. 148, 153;
+    variability of characters in breeds of pigeons, i. 161;
+    reversion of crossed pigeons to coloration of _Columba livia_, i. 198;
+    on pigeon-fancying, i. 206, 215-216;
+    on tumbler-pigeons, i. 209, ii. 242;
+    carrier-pigeon, i. 211;
+    effects of interbreeding on pigeons, ii. 126;
+    properties of pigeons, ii. 197-198;
+    death of short-faced tumblers in the egg, ii. 226;
+  {449}
+    Archangel pigeon, ii. 240.
+  ECHINODERMATA, metagenesis in, ii. 367.
+  _Ectopistes_, specific difference in number of tail-feathers in, i. 159.
+  _Ectopistes migratorius_, sterile hybrids of, with _Turtur vulgaris_, i.
+      193.
+  EDENTATA, correlation of dermal system and teeth in the, ii. 328.
+  EDGEWORTH, Mr., use of grass-seeds as food in the Punjab, i. 309.
+  EDMONSTON, Dr., on the stomach in _Larus argentatus_ and the raven, ii.
+      302.
+  EDWARDS and COLIN, on English wheat in France, ii. 307.
+  EDWARDS, W. F., absorption of the minority in crossed races, ii. 87.
+  EDWARDS, W. W., occurrence of stripes in a nearly thoroughbred horse, i.
+      57;
+    in foals of racehorses, i. 59.
+  EGGS, of fowls, characters of, i. 248;
+    variations of, in ducks, i. 281;
+    of the silkmoth, i. 301.
+  EGYPT, ancient dogs of, i. 17-18;
+    ancient domestication of the pigeon in, i. 204;
+    absence of the fowl in ancient, i. 246.
+  EGYPTIAN goose, hybrids of, with penguin duck, i. 282.
+  EHRENBERG, Prof., multiple origin of the dog, i. 16;
+    dogs of Lower Egypt, i. 25;
+    mummies of _Felis maniculata_, i. 43.
+  ELEMENT, male, compared to a premature larva, ii. 384.
+  ELEMENTS of the body, functional independence of the, ii. 368-371.
+  ELEPHANT, its sterility in captivity, ii. 150.
+  ELK, Irish, correlations in the, ii. 333-334.
+  ELLIOT, Sir Walter, on striped horses, i. 58;
+    Indian domestic and wild swine, i. 66;
+    pigeons from Cairo and Constantinople, i. 132;
+    fantail pigeons, i. 146;
+    Lotan tumbler pigeons, i. 150;
+    a pigeon uttering the sound _Yahu_, i. 155;
+    _Gallus bankiva_ in Pegu, i. 236.
+  ELLIS, Mr., varieties of cultivated plants in Tahiti, ii. 256.
+  ELM, nearly evergreen Cornish variety of the, i. 363, ii. 310;
+    foliage-varieties of the, i. 362.
+  ELM, weeping, i. 361;
+    not reproduced by seed, ii. 19.
+  _Emberiza passerina_, ii. 158.
+  EMBRYOS, similarity of, i. 12;
+    fusion of, ii. 339.
+  ENGEL, on _Laurus sassafras_, ii. 274.
+  ENGLAND, domestication of _Bos longifrons_ in, i. 81;
+    selection of horses in, in mediaeval times, ii. 203;
+    laws against the early slaughter of rams in, ii. 203.
+  EPHEMERIDAE, development of the, ii. 366.
+  _Epidendrum cinnabarinum_ and _E. zebra_, ii. 134.
+  EPILEPSY, hereditary, ii. 8, 78.
+  ERDT, disease of the white parts of cattle, ii. 337.
+  ERICACEAE, frequency of contabescence in the, ii. 165.
+  ERICHTHONIUS, an improver of horses by selection, ii. 202.
+  ERMAN, on the fat-tailed Kirghisian sheep, i. 98, ii. 280;
+    on the dogs of the Ostyaks, ii. 206.
+  _Erodium_, ii. 59.
+  _Erythrina Crista-galli_ and _E. herbacea_, hybrids of, ii. 265.
+  ESQUILANT, Mr., on the naked young of dun-coloured pigeons, i. 170.
+  ESQUIMAUX dogs, their resemblance to wolves, i. 21;
+    selection of, ii. 206.
+  EUDES-DESLONGCHAMPS, on appendages under the jaw of pigs, i. 75-76.
+  _Euonymus Japonicus_, i. 383.
+  EUROPEAN cultivated plants, still wild in Europe, i. 307.
+  EVANS, Mr., on the Lotan tumbler pigeon, i. 150.
+  EVELYN, pansies grown in his garden, i. 368.
+  EVEREST, R., on the Newfoundland dog in India, i. 36, ii. 305;
+    degeneration of setters in India, i. 38;
+    Indian wild boars, i. 66.
+  EWES, hornless, ii. 350.
+  EXTINCTION of domestic races, i. 221.
+  EYES, hereditary peculiarities of the, ii. 8-10;
+    loss of, causing microphthalmia in children, ii. 24;
+    modification of the structure of, by natural selection, ii. 222-223;
+    fusion of, ii. 341.
+  EYEBROWS, hereditary elongation of hairs in, ii. 8.
+  EYELIDS, inherited peculiarities of the, ii. 8.
+  EYTON, Mr., on gestation in the dog, i. 30;
+    variability in number of vertebrae in the pig, i. 74;
+    individual sterility, ii. 162.
+
+  _Faba vulgaris_, i. 330.
+  FABRE, observations on _Aegilops triticoides,_ i. 313.
+  _Fagus sylvatica_, ii. 19.
+  FAIRWEATHER, Mr., production of double flowers from old seed, ii. 167.
+  _Falco albidus_, resumption of young plumage by, in captivity, ii. 158.
+  _Falco ossifragus_, ii. 230.
+  _Falco subbuteo_, copulating in captivity, ii. 154.
+  _Falco tinnunculus_, breeding in captivity, ii. 154.
+  {450}
+  FALCONER, Dr., sterility of English bulldogs in India, i, 38;
+    resemblance between _Sivatherium_ and Niata cattle, i. 89;
+    selection of the silkworm in India, i. 301;
+    fastigate apple-trees in Calcutta, i. 361;
+    reproduction of a supernumerary thumb after amputation, ii. 14;
+    fertility of the dhole in captivity, ii. 151;
+    fertility of English dogs in India, ii. 161;
+    sterility of the tiger in captivity, ii. 151;
+    turkeys at Delhi, ii. 161;
+    on Indian cultivated plants, ii. 165;
+    Thibet mastiff and goat, ii. 278.
+  FALCONS, sterility of, in captivity, ii. 153.
+  FALKLAND Islands, horses of the, i. 52-53, 61;
+    feral pigs of the, i. 77;
+    feral cattle of the, i. 82, 86;
+    feral rabbits of the, i. 112.
+  FALLOW deer, ii. 103, 120.
+  FANTAIL pigeons, i. 146-148, ii. 227;
+    figured, i. 147;
+    furcula of, figured, i. 167;
+    history of, i. 208;
+    absence of oil-gland in, ii. 344.
+  FAROE Islands, pigeons of the, i. 183.
+  FASHION, influence of, in breeding, ii. 240.
+  FASTIGATE trees, ii. 277, 348.
+  FAUNAS, geographical differences, of, i. 10.
+  "FAVOURITE" bull, ii. 65, 118.
+  FEATHERS, homologous variation in, ii. 325.
+  FEET, of pigeons, individual differences of, i. 160;
+    correlations of external characters in, i. 170-171.
+  FEET and beak, correlation of, in pigeons, i. 171-174.
+  FELIDAE, fertility of, in captivity, ii. 150.
+  _Felis bubastes_, i. 43.
+  _Felis caffra_, i. 44.
+  _Felis caligulata_, i. 43.
+  _Felis chaus_, i. 43-44.
+  _Felis jubata_, ii. 151.
+  _Felis lybica_, i. 44.
+  _Felis maniculata_, i. 43.
+  _Felis manul_, i. 45.
+  _Felis ornata_, i. 45.
+  _Felis sylvestris_, i. 44.
+  _Felis torquata_, i. 45.
+  FEMALE, affected by male element, ii. 365, 387-388.
+  FEMALE flowers, in male panicle of maize, i. 321.
+  FENNEL, Italian variety of, i. 326.
+  FERAL cats, i. 47;
+    cattle, i. 86;
+    rabbits, i. 111-115;
+    Guinea fowl, i. 294;
+    animals and plants, reversion in, ii. 32-34, 47.
+  FERGUSON, Mr., supposed plurality of origin of domestic fowls, i. 231;
+    chickens of black game-fowls, i. 244;
+    relative size of eggs of fowls, i. 248;
+    yolk of eggs of game-fowls, i. 249;
+    early pugnacity of game-cocks, i. 250;
+    voice of the Malay fowl, i. 259;
+    effects of interbreeding on fowls, ii. 124;
+    selection in Cochin China fowls, ii. 196;
+    on fashion in poultry, ii. 240.
+  FERNANDEZ, on Mexican dogs, i. 23.
+  FERNS, reproduction of abnormal forms of, by spores, i. 383;
+    non-diffusion of cell-gemmules in, ii. 379.
+  FERRETS, ii. 111, 151, 206.
+  FERTILISATION, artificial, of the St. Valery apple, i. 350.
+  FERTILITY, various degrees of, in sheep, i. 97;
+    unlimited mutual, of breeds of pigeons, i. 192-194;
+    comparative of mongrels and hybrids, ii. 100-101, 178-180;
+    influence of nourishment on, ii. 111;
+    diminished by close interbreeding, ii. 118, 175;
+    reduced, of Chillingham wild cattle, ii. 119;
+    of domesticated varieties when crossed, ii. 189.
+  _Festuca_, species of, propagated by bulblets, ii. 170.
+  FILBERTS, spared by tomtits, ii. 231.
+  FILIPPI, on the breeding of branchiferous tritons, ii. 384.
+  FINCHES, general sterility of, in captivity, ii. 154.
+  FINNIKIN (pigeon), i. 156.
+  FINNOCHIO, i. 326.
+  FIR, Scotch, acclimatisation of, ii. 310.
+  FISH, Mr., advantage of change of soil to plants, ii. 147.
+  FISHES, regeneration of portions of fins of, ii. 15;
+    variability of, when kept in tanks, ii. 259;
+    marine, living in fresh water, ii. 304;
+    double monsters of, ii. 340.
+  FISSION and gemmation, ii. 358.
+  FITCH, Mr., persistency of a variety of the pea, i. 329.
+  FITTEST, survival of the, i. 6.
+  FITZINGER, origin of sheep, i. 94;
+    African maned sheep, i. 96.
+  FIXEDNESS of character, conditions of, discussed, ii. 62-64.
+  FLAX, found in the Swiss lake-dwellings, i. 317;
+    climatal difference in products of, ii. 274.
+  FLEECE, fineness of, in Austrian merinos, ii. 197.
+  FLEISCHMANN, on German sheep crossed with merinos, ii. 88-89.
+  "FLORENTINER-TAUBE," i. 142-143.
+  FLOUNDER, ii. 53.
+  FLOURENS, crossing of wolf and dog, i. 32;
+    prepotency of the jackal over the dog, ii. 67;
+    hybrids of the horse and ass, ii. 68;
+    breeding of monkeys in Europe, ii. 153.
+  {451}
+  FLOWER-GARDEN, earliest known, in Europe, ii. 217.
+  FLOWERS, capricious transmission of colour-varieties in, ii. 20-21;
+    tendency to uniformity in striped, ii. 70;
+    scorching of, dependent on colour, ii. 229;
+    change in, caused by conditions of life, ii. 273;
+    rudimentary, ii. 316;
+    relative position of, to the axis, ii. 345.
+  FOETATION, abdominal, ii. 294.
+  FOLEY, Mr., wild varieties of pears, ii. 260.
+  FOLIAGE, inherited peculiarities of, i. 362;
+    variegation, of, i. 366;
+    bud-variation in, i. 382-384.
+  FOOD, influence of, on the pig, i. 72;
+    on cattle, i. 91;
+    excess of, a cause of variability, ii. 257.
+  FORBES, D., on Chilian sheep, i. 95;
+    on the horses of Spain, Chili, and the Pampas, i. 52.
+  _Formica rufa_, ii. 251.
+  FORTUNE, R., sterility of the sweet potato in China, ii. 169;
+    development of axillary bulbs in the yam, _ibid._
+  FOWL, common, breeds of, i. 225-230;
+    supposed plurality of origin, i. 230;
+    early history of, i. 231-233;
+    causes of production of breeds of, i. 233;
+    origin of from _Gallus bankiva_, i. 236-239, 245;
+    feral, notices of, i. 237-238;
+    reversion and analogous variation in, i. 239-246, ii. 35, 38, 39, 40,
+        349, 350;
+    "cuckoo" sub-breeds of, i. 244;
+    history of, i. 246-247;
+    structural characters of, i. 247-250;
+    sexual peculiarities of, i. 251-257, ii. 74;
+    external differences of, i. 257-260;
+    differences of breeds of, from _G. bankiva_, i. 260;
+    osteological characters of, i. 260-270;
+    effects of disuse of parts in, i. 270-274, ii. 298;
+    feral, i. 190, ii. 33;
+    polydactylism in, ii. 14;
+    fertility of, increased by domestication, ii. 112, 167;
+    sterility of, under certain conditions, ii. 162;
+    influence of selection on, ii. 196, 198, 209, 210;
+    evils of close interbreeding of, ii. 124-125;
+    crossing of, ii. 95, 96, 97;
+    prepotency of transmission in, ii. 67;
+    rudimentary organs in, ii. 315;
+    crossing of non-sitting varieties of, ii. 43-44;
+    homology of wing and leg feathers in, ii. 323;
+    hybrids of, with pheasants and _Gallus Sonneratii_, ii. 45;
+    black-skinned, ii. 209-210;
+    black, preyed upon by the osprey in Iceland, ii. 230;
+    five-toed, mentioned by Columella, ii. 429;
+    rumpless, tailed chickens produced by, ii. 31;
+    Dorking, crosses of, ii. 93;
+    form of comb and colour of plumage in, ii. 238;
+    game, crossing of white and black, ii. 92;
+    five-spurred, ii. 391;
+    Spanish, liable to suffer from frost, ii. 306;
+    Polish, peculiarities of skull of, ii. 332-333.
+  FOX, sterility of, in captivity, ii. 151.
+  FOX, S. Bevan, races of bees, i. 298.
+  FOX, W. Darwin, gestation of the dog, i. 30;
+    "Negro" cat, i. 46;
+    reversion of sheep in colour, ii. 30;
+    period of gestation in the pig, i. 74;
+    young of the Himalayan rabbit, i. 109;
+    crossing of wild and domestic turkeys, i. 292;
+    reversion in crossed musk ducks, ii. 40;
+    spontaneous segregation of varieties of geese, ii. 104;
+    effects of close interbreeding  upon bloodhounds, ii. 121;
+    deafness of white cats with blue eyes, ii. 329.
+  FOXHOUNDS, i. 40, ii. 120.
+  _Fragaria chiloensis_, i. 351.
+  _Fragaria collina_, i. 351.
+  _Fragaria dioica_ of Duchesne, i. 353.
+  _Fragaria elatior_, i. 351.
+  _Fragaria grandiflora_, i. 351.
+  _Fragaria vesca_, i. 351.
+  _Fragaria virginiana_, i. 351.
+  _Fraxinus excelsior_, i. 360, 362, ii. 19.
+  _Fraxinus lentiscifolia_, ii. 19.
+  FRIESLAND cattle, probably descended from _Bos primigenius_, i. 81.
+  FRILLBACK (pigeon), i. 155;
+    Indian, i. 153.
+  _Fringilla ciris_, ii. 154.
+  _Fringilla spinus_, ii. 154.
+  FRIZZLED fowls, i. 230;
+    horses, i. 54.
+  FROG, polydactylism in the, ii. 14.
+  FRUIT, seedless, ii. 168.
+  FRUIT-TREES, varieties of, occurring wild, i. 310.
+  FRY, Mr., on fertile hybrid cats, i. 44;
+    on feral fowls in Ascension, i. 238.
+  FUCHSIAS, origin of, i. 364;
+    bud-variation in, i. 382.
+  _Fuchsia coccinea_ and _fulgens_, twin seed produced by crossing, i. 391.
+  FUEGIANS, their superstition about killing young water-fowl, i. 310;
+    selection of dogs by the, ii. 207;
+    their comparative estimation of dogs and old women, ii. 215;
+    their power of distant vision, ii. 223.
+  FUNGI, parasitic, ii. 284-285.
+  FURCULA, characters and variations of the, in pigeons, i. 167;
+    alteration of, by disuse, in pigeons, i. 175;
+    characters of, in fowls, i. 268.
+  FUSION of homologous parts, ii. 393.
+
+  GAIT, inheritance of peculiarities of, ii. 6.
+  GALAPAGOS Archipelago, its peculiar fauna and flora, i. 9.
+  _Galeobdolon luteum_, pelorism in, ii. 59, 345.
+  {452}
+  GALLS, ii. 282-284.
+  GALL-GNATS, ii. 283.
+  GALL-LIKE excrescences not inherited, ii. 23.
+  GALLINACEOUS birds, restricted range of large, i. 237;
+    general fertility of in captivity, ii. 155.
+  _Gallinula chloropus_, ii. 156.
+  _Gallinula nesiotis_, i. 287.
+  GALTON, Mr., fondness of savages for taming animals, i. 20, ii. 160;
+    cattle of Benguela, i. 88;
+    on hereditary talent, ii. 7.
+  GALLESIO, species of oranges, i. 334, 335, 336;
+    hybridisation of oranges, i. 336;
+    persistency of races in the peach, i. 339;
+    supposed specific distinctions of peach and nectarine, i. 340;
+    Bizzaria orange, i. 391;
+    crossing of red and white carnations, i. 393;
+    crossing of the orange and lemon, i. 399, ii. 365;
+    effect of foreign pollen on maize, i. 400;
+    spontaneous crossing of oranges, ii. 91;
+    monstrosities a cause of sterility in plants, ii. 166;
+    seeding of ordinarily seedless fruits, ii. 168;
+    sterility of the sugar cane, ii. 169;
+    tendency of male flowers to become double, ii. 171;
+    effects of selection in enlarging fruit, &c., ii. 217;
+    variation of the orange tree in North Italy, ii. 256;
+    naturalisation of the orange in Italy, ii. 309.
+  _Gallus aeneus_, a hybrid of _G. varius_ and the domestic fowl, i. 235.
+  _Gallus bankiva_, probable original of domestic fowls, i. 233, 236-239,
+      245;
+    game-fowl, nearest to, i. 226;
+    crossed with _G. Sonneratii_, i. 234;
+    its character and habits, i. 235-236, ii. 109;
+    differences of various breeds of fowls from, i. 260;
+    occipital foramen of, figured, i. 261;
+    skull of, figured, i. 262;
+    cervical vertebra of, figured, i. 267;
+    furcula of, figured, i. 268;
+    reversion to, in crossed fowls, ii. 39-40;
+    hybrid of, with _G. varius_, i. 235, ii. 40;
+    number of eggs of, ii. 112.
+  _Gallus ferrugineus_, i. 226.
+  _Gallus furcatus_, i. 234.
+  _Gallus giganteus_, i. 235.
+  _Gallus Sonneratii_, characters and habits of, i. 233;
+    hybrids of, i. 234, ii. 45.
+  _Gallus Stanleyi_, hybrids of, i. 234.
+  _Gallus Temminckii_, probably a hybrid, i. 235.
+  _Gallus varius_, character and habits of, i. 234;
+    hybrids and probable hybrids of, i. 234-235.
+  GAMBIER, Lord, his early cultivation of the pansy, i. 368.
+  GAME-FOWL, i. 226, 250, 251, 252.
+  GAPES, ii. 228.
+  GARCILAZO de la Vega, annual hunts of the Peruvian Incas, ii. 207.
+  GARNETT, Mr., migratory propensities of hybrid ducks, ii. 45.
+  GARROD, Dr., on hereditary gout, ii. 7.
+  GASPARINI, a genus of pumpkins, founded on stigmatic characters, i. 359.
+  GAUDICHAUD, bud-variation in the pear, i. 376;
+    apple tree with two kinds of fruit on branch, i. 392.
+  GAUDRY, anomalous structure in the feet of horses, i. 50.
+  GAY, on _Fragaria grandiflora_, i. 351;
+    on _Viola lutea_ and _tricolor_, i. 368;
+    on the nectary of _Viola grandiflora_, i. 369.
+  GAYAL, domestication of the, i. 82.
+  GAYOT, _see_ Moll.
+  GAERTNER, on the sterility of hybrids, i. 192, ii. 101;
+    acquired sterility of varieties of plants when crossed, i. 358;
+    sterility in transplanted plants, and in the lilac in Germany, ii. 164;
+    mutual sterility of blue and red flowers of the pimpernel, ii. 190;
+    supposed rules of transmission in crossing plants, ii. 68;
+    on crossing plants, ii. 98, 127, 130, 131;
+    on repeated crossing, ii. 267;
+    absorption of one species by another, when crossed, ii. 88;
+    crossing of varieties of the pea, i. 397;
+    crossing maize, ii. 105;
+    crossing of species of _Verbascum_, ii. 93, 105;
+    reversion in hybrids, ii. 36, 49, 50;
+    of _Cereus_, i. 392;
+    of _Tropaeolum majus_ and _minus_, i. 392;
+    variability of hybrids, ii. 265;
+    variable hybrids from one variable parent, ii. 270;
+    graft hybrid produced by inosculation in the vine, i. 395;
+    effect produced by grafts on the stock, i. 394, ii. 278;
+    tendency of hybrid plants to produce double flowers, ii. 171;
+    production of perfect fruit by sterile hybrids, ii. 172;
+    sexual elective affinity, ii. 180;
+    self-impotence in _Lobelia_, _Verbascum_, _Lilium_, and _Passiflora_,
+        ii. 136-137;
+    on the action of pollen, ii. 108;
+    fertilisation of _Malva_, i. 402-403, ii. 363;
+    prepotency of pollen, ii. 187;
+    prepotency of transmission in species of _Nicotiana_, ii. 67;
+    bud-variation in _Pelargonium zonale_, i. 375;
+    in _Oenothera biennis_, i. 382;
+    in _Achillaea millefolium_, i. 408;
+    effect of manure on the fertility of plants, ii. 163;
+    on contabescence, ii. 165-166;
+    inheritance of plasticity, ii. 241;
+    villosity of plants, ii. 277.
+  GEESE (_anseres_) general fertility of, in captivity, ii. 157.
+  GEGENBAUR, on the number of digits, ii. 13.
+  GEMMATION and fission, ii. 358.
+  {453}
+  GEMMULES, or cell-gemmules, ii. 374, 378-381, 384.
+  GENET, fertility of the, in captivity, ii. 151.
+  GENERATION, alternate, ii. 361, 367, 390.
+  GENERATION, sexual, ii. 359-364.
+  GENIUS, inheritance of, ii. 7.
+  _Gentiana amarella_, ii. 168.
+  GEOFFROY Saint-Hilaire, production of monstrous chickens, ii. 289;
+    "_Loi de l'affinite de soi pour soi_," ii. 339;
+    compensation of growth, ii. 342.
+  GEOFFROY Saint-Hilaire, Isid., origin of the dog, i. 66;
+    barking of a jackal, i. 27;
+    period of gestation and odour of the jackal, i. 30;
+    anomalies in the teeth of dogs, i. 34;
+    variations in the proportions of dogs, i. 35;
+    webbed feet of Newfoundland dogs, i. 39;
+    crossing of domestic and wild cats, i. 44;
+    domestication of the arni, i. 82;
+    supposed introduction of cattle into Europe from the East, _ibid._;
+    absence of interdigital pits in sheep, i. 95;
+    origin of the goat, i. 101;
+    feral geese, i. 190;
+    ancient history of the fowl, i. 246;
+    skull of the Polish fowl, i. 262;
+    preference of the Romans for the liver of white geese, i. 289;
+    polydactylism, ii. 12;
+    assumption of male characters by female birds, ii. 51;
+    supernumerary mammae in women, ii. 58;
+    development of a proboscis in the pig, _ibid._;
+    transmission and blending of characters in hybrids, ii. 94;
+    refusal of animals to breed in captivity, ii. 149;
+    on the Guinea pig, ii. 152;
+    silkworms producing white cocoons, ii. 199;
+    on the carp, ii. 236;
+    on _Helix lactea_, ii. 280;
+    on monstrosities, ii. 254;
+    injury to the embryo a cause of monstrosity, ii. 269;
+    alteration in the coat of horses in coal mines, ii. 278;
+    length of the intestines in wild and tame animals, ii. 302-303;
+    inheritance of rudimentary limbs in the dog, ii. 315;
+    correlation in monstrosities, ii. 320;
+    supernumerary digits in man, ii. 322;
+    co-existence of anomalies, ii. 331;
+    fusion of homologous parts, ii. 341-342;
+    presence of hairs and teeth in ovarian tumours, ii. 370;
+    development of teeth on the palate in the horse, ii. 391.
+  GEOGRAPHICAL differences of faunas, i. 10.
+  GEOLOGICAL succession of organisms, i. 11.
+  _Geranium_, ii. 59.
+  _Geranium phaeum_ and _pyrenaicum_, ii. 258.
+  _Geranium pratense_, i. 379.
+  GERARD, asserted climatal change in Burgundian bees, i. 297.
+  GERARDE, on varieties of the hyacinth, i. 370.
+  GERSTAECKER, on hive-bees, i. 299.
+  GERVAIS, Prof., origin of the dog, i. 16;
+    resemblance of dogs and jackals, i. 24;
+    taming of the jackal, i. 26;
+    number of teeth in dogs, i. 34;
+    breeds of dogs, i. 36;
+    on tertiary horses, i. 51;
+    biblical notices of horses, i. 55;
+    species of _Ovis_, i. 94;
+    wild and domestic rabbits, i. 103;
+    rabbits from Mount Sinai and Algeria, i. 105;
+    earless rabbits, i. 108;
+    batrachia with doubled limbs, ii. 391.
+  GESTATION, period of, in the dog, wolf, &c, i. 29-30;
+    in the pig, i. 74;
+    in cattle, i. 87, ii. 321;
+    in sheep, i. 97.
+  GESTURES, inheritance of peculiarities in, ii. 6.
+  "GHOONDOOKS" a sub-breed of fowls, i. 229.
+  GHOR-KHUR, ii. 42.
+  GILES, Mr., effect of cross-breeding in the pig, i. 404.
+  GIRAFFE, co-ordination of structure of, ii. 221.
+  GIRARD, period of appearance of permanent teeth in dogs, i. 35.
+  GIROU de Buzareingues, inheritance in the horse, ii. 10;
+    reversion by age in cattle, ii. 38;
+    prepotency of transmission of character in sheep and cattle, ii. 66;
+    on crossing gourds, ii. 108.
+  GISBURNE, wild cattle at, i. 84.
+  _Gladiolus_, i. 364;
+    self-impotence of hybrids of, ii. 139.
+  _Gladiolus colvillii_, bud-variation in, i. 382.
+  GLANDS, compensatory development of, ii. 300.
+  GLASTONBURY thorn, i. 364.
+  GLENNY, Mr., on the _Cineraria_, ii. 200.
+  GLOEDE, F., on strawberries, i. 353.
+  GLOGER, on the wings of ducks, ii. 298.
+  "GLOUGLOU" (pigeon), i. 154.
+  _Gloxiniae_, peloric, i. 365, ii. 167.
+  GMELIN, on red cats, at Tobolsk, i. 47.
+  GOAT, i. 101-102, ii. 33;
+    polydactylism in the, ii. 14;
+    sexual differences in horns of, ii. 73;
+    valued by South Africans, ii. 207;
+    Thibet, ii. 278;
+    amount of milk and development of udders in the, ii. 300;
+    hornless, rudimentary bony cores in, ii. 316;
+    Angora, ii. 326.
+  GODRON, odour of the hairless Turkish dog, i. 30;
+    differences in the skull of dogs, i. 34;
+    increase of breeds of horses, i. 51;
+    crossing of domestic and wild swine, i. 66;
+    on goats, i. 101-102;
+    colour of the skin in fowls, i. 258;
+    bees of north and south of France, i. 297;
+    introduction of the silkworm into Europe, i. 300;
+    variability in the silkworm, i. 304;
+    supposed species of wheat, i. 312-314;
+    on _Aegilops triticoides_, i. 313;
+    variable presence of barbs in grasses, i. 314;
+  {454}
+    colours of the seeds of maize, i. 321;
+    unity of character in cabbages, i. 323;
+    correlation of colour and odour, i. 325;
+    effect of heat and moisture on the cabbage, i. 325;
+    on the cultivated species of _Brassica_, i. 325;
+    on the Rouncival and sugar peas, i. 327;
+    variation in the numbers of peas in the same pod, i. 328;
+    wild vines in Spain, i. 332;
+    on raising peaches from seed, i. 339;
+    supposed specific distinctness of peach and nectarine, i. 340;
+    nectarine producing peaches, i. 341;
+    on the flower of _Corydalis_, i. 344;
+    origin and variations of the plum, i. 345;
+    origin of the cherry, i. 347;
+    reversion of single-leaved strawberries, i. 353;
+    five-leaved variety of _Fragaria collina_, i. 353;
+    supposed immutability of specific characters, i. 358-359;
+    varieties of _Robinia_, i. 361;
+    permanency of the simple-leaved ash, i. 362;
+    non-inheritance of certain mutilations, ii. 23;
+    wild turnips, carrots, and celery, ii. 33;
+    pre-potency of a goat-like ram, ii. 66;
+    benefit of change of soil to plants, ii. 146;
+    fertility of peloric flowers of _Corydalis solida_, ii. 167;
+    seeding of ordinarily seedless fruit, ii. 168;
+    sexual sterility of plants propagated by buds, &c., ii. 169;
+    increase of sugar in beet-root, ii. 201;
+    effects of selection in enlarging particular parts of plants, ii. 217;
+    growth of the cabbage in the tropics, ii. 277;
+    rejection of bitter almonds by mice, ii. 232;
+    influence of marshy pasture on the fleece of sheep, ii. 278;
+    on the ears of ancient Egyptian pigs, ii. 301;
+    primitive distinctness of species, ii. 415;
+    solid hoofed swine, ii. 429.
+  GOETHE, on compensation of growth, ii. 342.
+  GOLDFISH, i. 296-297, ii. 236.
+  GOMARA, on South American cats, i. 46.
+  GONGORA, number of seeds in the, ii. 379.
+  GOOSE, ancient domestication of, i. 287;
+    sacred to Juno in Rome, _ibid._;
+    inflexibility of organisation of, i. 288;
+    skull perforated in tufted, i. 288;
+    characters of breeds and sub-breeds of, i. 288-289;
+    variety of, from Sebastopol, i. 289, ii. 392;
+    feral in La Plata, i. 190;
+    Egyptian, hybrid of, with penguin duck, ii. 68;
+    spontaneous segregation of varieties of, ii. 104;
+    fertility of, increased by domestication, ii. 112;
+    decreased fertility of, in Bogota, ii. 161;
+    sterility of, in the Philippine Islands, ii. 162;
+    selection of, ii. 204;
+    white, preference of the Romans for the liver of, ii. 209;
+    persistency of character in, ii. 254;
+    Egyptian, change in breeding season of, ii. 304.
+  GOOSEBERRY, i. 354-356;
+    bud-variation in the, i. 376;
+    Whitesmith's, ii. 232.
+  GOEPPERT, on monstrous poppies, ii. 166.
+  GOSSE, P. H., feral dogs in Jamaica, i. 28;
+    feral pigs of Jamaica, i. 77-78;
+    feral rabbits of Jamaica, i. 112;
+    on _Columba leucocephala_, i. 183;
+    feral Guinea fowl in Jamaica, i. 190;
+    reproduction of individual peculiarities by gemmation in a coral, i.
+        374;
+    frequency of striped legs in mules, ii. 42.
+  GOULD, Dr., on hereditary haemorrhage, ii. 7.
+  GOULD, John, origin of the turkey, i. 292.
+  _Goura coronata_ and _Victoriae_, hybrids of, i. 194, ii. 155.
+  GOURDS, i. 357;
+    crossing of varieties of, ii. 108;
+    ancient Peruvian variety of, ii. 429.
+  GOUT, inheritance of, ii. 7;
+    period of appearance of, ii. 77.
+  GRABA, on the pigeon of the Faroe islands, i. 183.
+  GRAFTING, ii. 147;
+    effects of, ii. 259, 278;
+    upon the stock, i. 394-395;
+    upon the variability of trees, ii. 259;
+    changes analogous to bud-variation produced by, i. 387, 389.
+  GRAFT-HYBRIDS, i. 390-391, 394-397, ii. 364-365.
+  GRAPES, bud-variation in, i. 375;
+    cross of white and purple, i. 393;
+    green, liable to disease, ii. 336;
+    effect of foreign pollen on, i. 400.
+  GRASSES, seeds of, used as food by savages, i. 307-309.
+  GRAY, Asa, superior wild varieties of fruit-trees, i. 310;
+    cultivated native plants of North America, i. 312, 357;
+    non-variation of weeds, i. 317;
+    supposed spontaneous crossing of pumpkins, i. 399;
+    pre-ordination of variation, ii. 432;
+    progeny of husked form of maize, i. 320;
+    wild intermediate forms of strawberries, i. 352.
+  GRAY, G. R., on _Columba gymnocyclus_, i. 184.
+  GRAY, J. E., on _Sus pliciceps_, i. 70;
+    on a variety of the gold-fish, i. 297;
+    hybrids of the ass and zebra, ii. 42-43;
+    on the breeding of animals at Knowsley, ii. 149;
+    on the breeding of birds in captivity, ii. 157.
+  GREENE, J. Reay, on the development of the echinodermata, ii. 367.
+  GREENHOW, Mr., on a Canadian web-footed dog, i. 39.
+  GREENING, Mr., experiments on _Abraxas grossulariata_, ii. 280.
+  GREGSON, Mr., experiments on _Abraxas grossulariata_, ii. 280.
+  GREY, Sir George, preservation of seed-bearing plants by the Australian
+      savages, i. 310;
+  {455}
+    detestation of incest by Australian savages, ii. 123.
+  GREYHOUNDS, sculptured on Egyptian monuments, and in the Villa of
+      Antoninus, i. 17;
+    modern breed of, i. 41;
+    crossed with the bulldog, by Lord Orford, ii. 95;
+    co-ordination of structure of, due to selection, ii. 221-222;
+    Italian, ii. 227.
+  GREYNESS, inherited at corresponding periods of life, ii. 77.
+  GRIEVE, Mr., on early-flowering dahlias, i. 370.
+  GRIGOR, Mr., acclimatisation of the Scotch fir, ii. 310.
+  GROOM-NAPIER, C. O., on the webbed feet of the otter-hound, i. 40.
+  "GROSSES-GORGES" (pigeons), i. 137.
+  GROUND-TUMBLER, Indian, i. 150.
+  GROUSE, fertility of, in captivity, ii. 156.
+  GROENLAND, hybrids of _Aegilops_ and wheat, ii. 110.
+  _Grus montigresia_, _cinerea_, and _Antigone_, ii. 156.
+  GUANACOS, selection of, ii. 207.
+  GUANS, general fertility of, in captivity, ii. 156.
+  GUELDER-ROSE, ii. 185.
+  GUELDERLAND fowls, i. 230.
+  GUIANA, selection of dogs by the Indians of, ii. 206.
+  GUINEA FOWL, i. 294;
+    feral in Ascension, and Jamaica, i. 190, ii. 33;
+    indifference of to change of climate, ii. 161.
+  GUINEA pig, ii. 24, 152.
+  GUELDENSTADT, on the jackal, i. 25.
+  GULL, herring, breeding in confinement, ii. 157.
+  GULLS, general sterility of, in captivity, ii. 157.
+  _Gulo_, sterility of, in captivity, ii. 152.
+  GUENTHER, A., on tufted ducks and geese, i. 274;
+    on the regeneration of lost parts in batrachia, ii. 15.
+  GURNEY, Mr., owls breeding in captivity, ii. 154;
+    appearance of "black-shouldered" among ordinary peacocks, i. 291.
+
+  HABIT, influence of, in acclimatisation, ii. 312-315.
+  HABITS, inheritance of, ii. 395.
+  HAECKEL, on cells, ii. 370;
+    on the double reproduction of medusae, ii. 384;
+    on inheritance, ii. 397.
+  HACKLES, peculiarities of, in fowls, i. 254.
+  HAIR, on the face, inheritance of, in man, ii. 4;
+    peculiar lock of, inherited, ii. 5;
+    growth of, under stimulation of skin, ii. 326;
+    homologous variation of, ii. 325;
+    development of, within the ears and in the brain, ii. 391.
+  HAIR and teeth, correlation of, ii. 326-328.
+  HAIRY family, corresponding period of inheritance in, ii. 77.
+  HALF-CASTES, character of, ii. 46.
+  HALF-LOP rabbits, figured and described, i. 107-108;
+    skull of, i. 119.
+  _Haliaetus leucocephalus_, copulating in captivity, ii. 154.
+  HALLAM, Col., on a two-legged race of pigs, ii. 4.
+  HAMBURGH fowl, i. 227, 261;
+    figured, i. 228.
+  HAMILTON, wild cattle of, i. 84.
+  HAMILTON, Dr., on the assumption of male plumage by the hen pheasant, ii.
+      51.
+  HAMILTON, F. Buchanan, on the shaddock, i. 335;
+    varieties of Indian cultivated plants, ii. 256.
+  HANCOCK, Mr., sterility of tamed birds, ii. 155-157.
+  HANDWRITING, inheritance of peculiarities in, ii. 6.
+  HANMER, Sir J., on selection of flower seeds, ii. 204.
+  HANSELL, Mr., inheritance of dark yolks in duck's eggs, i. 281.
+  HARCOURT, E. V., on the Arab boar-hound, i. 17;
+    aversion of the Arabs to dun-coloured horses, i. 55.
+  HARDY, Mr., effect of excess of nourishment on plants, ii. 257.
+  HARE, hybrids of, with rabbit, i. 105;
+    sterility of the, in confinement, ii. 152;
+    preference of, for particular plants, ii. 232.
+  HARE-LIP, inheritance of, ii. 24.
+  HARLAN, Dr., on hereditary diseases, ii. 7.
+  HARMER, Mr., on the number of eggs in a codfish, ii. 379.
+  HARVEY, Mr., monstrous red and white African bull, i. 91.
+  HARVEY, Prof., singular form of _Begonia frigida_, i. 365-366;
+    effects of cross-breeding on the female, i. 404;
+    monstrous saxifrage, ii. 166.
+  HASORA wheat, i. 313.
+  HAUTBOIS strawberry, i. 353.
+  HAWKER, Col., on call or decoy ducks, i. 281.
+  HAWTHORN, varieties of, i. 360-364;
+    pyramidal, i. 361;
+    pendulous hybridised, ii. 18;
+    changes of, by age, i. 364, 387;
+    bud-variation in the, i. 377;
+    flower buds of, attacked by bullfinches, ii. 232.
+  HAYES, Dr., character of Esquimaux dogs, i. 21-22.
+  HAYWOOD, W., on the feral rabbits of Porto Santo, i. 114.
+  HAZEL, purple-leaved, i. 362, 395, ii. 330.
+  HEAD of wild boar and Yorkshire pig, figured, i. 72.
+  {456}
+  HEAD and limbs, correlated variability of, ii. 323.
+  HEADACHE, inheritance of, ii. 79.
+  HEARTSEASE, i. 368-369;
+    change produced in the, by transplantation, i. 386;
+    reversion in, ii. 31, 47;
+    effects of selection on, ii. 200;
+    scorching of, ii. 229;
+    effects of seasonal conditions on the, ii. 274;
+    annual varieties of the, ii. 305.
+  HEAT, effect of, upon the fleece of sheep, i. 98.
+  HEBER, Bishop, on the breeding of the rhinoceros in captivity, ii. 150.
+  HEBRIDES, cattle of the, i. 80;
+    pigeons of the, i. 183.
+  HEER, O., on the plants of the Swiss lake-dwellings, i. 309, ii. 215,
+      427;
+    on the cereals, i. 317-319;
+    on the peas, i. 326;
+    on the vine growing in Italy in the bronze age, i. 332.
+  _Helix lactea_, ii. 280.
+  _Hemerocallis fulva_ and _flava_, interchanging by bud-variation, i. 386.
+  HEMLOCK yields no conicine in Scotland, ii. 274.
+  HEMP, differences of, in various parts of India, ii. 165;
+    climatal difference in products of, ii. 274.
+  HEMPSEED, effect of, upon the colour of birds, ii. 280.
+  HERMAPHRODITE flowers, occurrence of, in Maize, i. 321.
+  HEN, assumption of male characters by the, ii. 51, 54;
+    development of spurs in the, ii. 318.
+  "HENNIES," or hen-like male fowls, i. 252.
+  HENRY, T. A., a variety of the ash produced by grafting, i. 394;
+    crossing of species of _Rhododendron_ and _Arabis_, i. 400.
+  HENSLOW, Prof., individual variation in wheat, i. 314;
+    bud-variation in the Austrian bramble rose, i. 381;
+    partial reproduction of the weeping ash by seed, ii. 19.
+  HEPATICA, changed by transplantation, i. 386.
+  HERBERT, Dr., variations of _Viola grandiflora_, i. 368;
+    bud-variation in camellias, i. 377;
+    seedlings from reverted _Cytisus Adami_, i. 388;
+    crosses of Swedish and other turnips, ii. 93;
+    on hollyhocks, ii. 107;
+    breeding of hybrids, ii. 131;
+    self-impotence in hybrid hippeastrums, ii. 138-139;
+    hybrid _Gladiolus_, ii. 139;
+    on _Zephyranthes candida_, ii. 164;
+    fertility of the crocus, ii. 165;
+    on contabescence, ii. 165;
+    hybrid _Rhododendron_, ii. 265.
+  HERCULANEUM, figure of a pig found in, i. 67.
+  HERON, Sir R., appearance of "black-shouldered" among ordinary peacocks,
+      i. 290-291;
+    non-inheritance of monstrous characters by goldfish, i. 296;
+    crossing of white and coloured Angora rabbits, ii. 92;
+    crosses of solid-hoofed pigs, ii. 93.
+  _Herpestes fasciatus_ and _griseus_, ii. 151.
+  HEUSINGER, on the sheep of the Tarentino, ii. 227;
+    on correlated constitutional peculiarities, ii. 337.
+  HEWITT, Mr., reversion in bantam cocks, i. 240;
+    degeneration of silk fowls, i. 243;
+    partial sterility of hen-like male fowls, i. 252;
+    production of tailed chickens by rumpless fowls, i. 259;
+    on taming and rearing wild ducks, i. 278-279, ii. 233, 262-263;
+    conditions of inheritance in laced Sebright bantams, ii. 22;
+    reversion in rumpless fowls, ii. 31;
+    reversion in fowls by age, ii. 39;
+    hybrids of pheasant and fowl, ii. 45, 68;
+    assumption of male characters by female pheasants, ii. 51;
+    development of latent characters in a barren bantam hen, ii. 54;
+    mongrels from the silk-fowl, ii. 67;
+    effects of close interbreeding on fowls, ii. 124-125;
+    on feathered-legged bantams, ii. 323.
+  HIBBERT, Mr., on the pigs of the Shetland Islands, i. 70.
+  HIGHLAND cattle, descended from _Bos longifrons_, i. 81.
+  HILDEBRAND, Dr., on the fertilisation of _Orchideae_, i. 402-403;
+    occasional necessary crossing of plants, ii. 90;
+    on _Primula sinensis_ and _Oxalis rosea_, ii. 132;
+    on _Corydalis cava_, ii. 132-133.
+  HILL, R., on the Alco, i. 31;
+    feral rabbits in Jamaica, i. 112;
+    feral peacocks in Jamaica, i. 190;
+    variation of the Guinea fowl in Jamaica, i. 294;
+    sterility of tamed birds in Jamaica, ii. 155, 157.
+  HIMALAYA, range of gallinaceous birds in the, i. 237.
+  HIMALAYAN rabbit, i. 107, 108-111;
+    skull of, i. 120.
+  HIMALAYAN sheep, i. 95.
+  HINDMARSH, Mr., on Chillingham cattle, i. 84.
+  "HINKEL-TAUBE," i. 142-143.
+  HINNY and mule, difference of, ii. 67-68.
+  _Hipparion_, anomalous resemblance to in horses, i. 50.
+  _Hippeastrum_, hybrids of, ii. 138-139.
+  HIVE-BEES, ancient domestication of, i. 297;
+    breeds of, i. 298;
+    smaller when produced in old combs, i. 297;
+    variability in, i. 298;
+    crossing of Ligurian and common, i. 299.
+  "HOCKER-TAUBE," i. 141.
+  HOBBS, Fisher, on interbreeding pigs, ii. 121.
+  HODGKIN, Dr., on the attraction of foxes by a female Dingo, i. 31;
+  {457}
+    origin of the Newfoundland dog, i. 42;
+    transmission of a peculiar lock of hair, ii. 5.
+  HODGSON, Mr., domestication of _Canis primaevus_, i. 26;
+    development of a fifth digit in Thibet mastiffs, i. 35;
+    number of ribs in humped cattle, i. 79;
+    on the sheep of the Himalaya, i. 95;
+    presence of four mammae in sheep, _ibid._;
+    arched nose in sheep, i. 96;
+    measurements of the intestines of goats, i. 102;
+    presence of interdigital pits in goats, _ibid._;
+    disuse a cause of drooping ears, ii. 301.
+  HOFACKER, persistency of colour in horses, i. 51, ii. 21;
+    production of dun horses from parents of different colours, i. 59;
+    inheritance of peculiarities in handwriting, ii. 6;
+    heredity in a one-horned stag, ii. 12;
+    on consanguineous marriages, ii. 123.
+  HOG, Red River, ii. 150.
+  HOGG, Mr., retardation of breeding in cows by hard living, ii. 112.
+  HOLLAND, Sir H., necessity of inheritance, ii. 2;
+    on hereditary diseases, ii. 7;
+    hereditary peculiarity in the eyelid, ii. 8;
+    morbid uniformity in the same family, ii. 17;
+    transmission of hydrocele through the female, ii. 52;
+    inheritance of habits and tricks, ii. 395.
+  HOLLY, varieties of the, i. 360, 362;
+    bud-reversion in, i. 384;
+    yellow-berried, ii. 19, 230.
+  HOLLYHOCK, bud-variation in, i. 378;
+    non-crossing of double varieties of, ii. 107;
+    tender variety of the, ii. 310.
+  HOMER, notice of Geese, i. 287;
+    breeding of the horses of Aeneas, ii. 202.
+  HOMOLOGOUS parts, correlated variability of, ii. 322-331, 354-355;
+    fusion of, ii. 393;
+    affinity of, ii. 339-342.
+  HOOFS, correlated with hair in variation, ii. 325.
+  HOOK-BILLED DUCK, skull figured, i. 282.
+  HOOKER, Dr. J. D., forked shoulder-stripe in Syrian asses, i. 63;
+    voice of the cock in Sikkim, i. 259;
+    use of Arum-roots as food, i. 307;
+    native useful plants of  Australia, i. 311;
+    wild walnut of the Himalayas, i. 356;
+    variety of the plane tree, i. 362;
+    production of _Thuja orientalis_ from seeds of _T. pendula_, i. 362;
+    singular form of _Begonia frigida_, i. 365;
+    reversion in plants run wild, ii. 33;
+    on the sugar-cane, ii. 169;
+    on Arctic plants, ii. 256;
+    on the oak grown at the Cape of Good Hope, ii. 274;
+    on _Rhododendron ciliatum_, ii. 277;
+    stock and mignonette, perennial in Tasmania, ii. 305.
+  HOPKIRK, Mr., bud-variation in the rose, i. 381;
+    in _Mirabilis jalapa_, i. 382;
+    in _Convolvulus tricolor_, i. 408.
+  HORNBEAM, heterophyllous, i. 362.
+  HORNED fowl, i. 229;
+    skull figured, i. 265.
+  HORNLESS cattle in Paraguay, i. 89.
+  HORNS of sheep, i. 95;
+    correlation of, with fleece in sheep, ii. 326;
+    correlation of, with the skull, ii. 333;
+    rudimentary in young polled cattle, ii. 315;
+    of goats, i. 102.
+  HORSES, in Swiss lake-dwellings, i. 49;
+    different breeds of, in Malay Archipelago, i. 49;
+    anomalies in osteology and dentition of, i. 50;
+    mutual fertility of different breeds, i. 51;
+    feral, i. 51;
+    habit of scraping away snow, i. 53;
+    mode of production of breeds of, i. 54;
+    inheritance and diversity of colour in, i. 55;
+    dark stripes in, i. 56-61, ii. 351;
+    dun-coloured, origin of, i. 59;
+    colours of feral, i. 60-61;
+    effect of fecundation by a Quagga on the subsequent progeny of, i.
+        403-404;
+    inheritance of peculiarities in, ii. 10-11;
+    polydactylism in, ii. 14;
+    inheritance of colour in, ii. 21;
+    inheritance of exostoses in legs of, ii. 23;
+    reversion in, ii. 33, 41;
+    hybrids of, with ass and zebra, ii. 42;
+    prepotency of transmission in the sexes of, ii. 65;
+    segregation of, in Paraguay, ii. 102;
+    wild species of, breeding in captivity, ii. 150;
+    curly, in Paraguay, ii. 205, 325;
+    selection of, for trifling characters, ii. 209;
+    unconscious selection of, ii. 212-213;
+    natural selection in Circassia, ii. 225;
+    alteration of coat of, in coal-mines, ii. 278;
+    degeneration of, in the Falkland Islands, ii. 278;
+    diseases of, caused by shoeing, ii. 300;
+    feeding on meat, ii. 305;
+    white and white-spotted, poisoned by mildewed vetches, ii. 337;
+    analogous variations in the colour of, ii. 349;
+    teeth developed on palate of, ii. 391;
+    of bronze period in Denmark, ii. 427.
+  HORSE-CHESNUT, early, at the Tuileries, i. 362;
+    tendency to doubleness in, ii. 168.
+  HORSE-RADISH, general sterility of the, ii. 170.
+  "HOUDAN," a French sub-breed of fowls, i. 229.
+  HOWARD, C., on an Egyptian monument, i. 17;
+    on crossing sheep, ii. 95, 120.
+  HUC, on the Emperor Khang-hi, ii. 205;
+    Chinese varieties of the bamboo, ii. 256.
+  HUMBOLDT, A., character of the Zambos, ii. 47;
+    parrot speaking the language of an extinct tribe, ii. 154;
+    on _Pulex penetrans_, ii. 275.
+  HUMIDITY, injurious effect of, upon horses, i. 53.
+  HUMPHREYS, Col., on Ancon sheep, i. 100.
+  HUNGARIAN cattle, i. 80.
+  {458}
+  HUNTER, John, period of gestation in the dog, i. 29;
+    on secondary sexual characters, i. 179;
+    fertile crossing of _Anser ferus_ and the domestic goose, i. 288;
+    inheritance of peculiarities in gestures, voice, &c., ii. 6;
+    assumption of male characters by the human female, ii. 51;
+    period of appearance of hereditary diseases, ii. 78;
+    graft of the spur of a cock upon its comb, ii. 296;
+    on the stomach of _Larus tridentatus_, ii. 302;
+    double-tailed lizards, ii. 341.
+  HUNTER, W., evidence against the influence of imagination upon the
+      offspring, ii. 264.
+  HUTTON, Capt., on the variability of the silk moth, i. 303;
+    on the number of species of silkworms, i. 300;
+    markings of silkworms, i. 302;
+    domestication of the rock-pigeon in India, i. 185;
+    domestication and crossing of _Gallus bankiva_, i. 236.
+  HUTCHINSON, Col., liability of dogs to distemper, i. 35.
+  HUXLEY, Prof., on the transmission of polydactylism, ii. 13;
+    on unconscious selection, ii. 194;
+    on correlation in the mollusca, ii. 320;
+    on gemmation and fission, ii. 359;
+    development of star-fishes, ii. 366.
+  HYACINTHS, i. 370-371;
+    bud-variation in, i. 385;
+    graft-hybrid by union of half bulbs of, i. 395;
+    white, reproduced by seed, ii. 20;
+    red, ii. 229, 336;
+    varieties of, recognisable by the bulb, ii. 251.
+  HYACINTH, feather, ii. 185, 316.
+  _Hyacinthus orientalis_, i. 370.
+  _Hybiscus syriacus_, ii. 286.
+  HYBRIDS, of hare and rabbit, i. 105;
+    of various species of _Gallus_, i. 234-236;
+    of almond, peach, and nectarine, i. 339;
+    naturally produced, of species of _Cytisus_, i. 390;
+    from twin-seed of _Fuchsia coccinea_ and _fulgens_, i. 391;
+    reversion of, i. 392-394, ii. 36, 48-50;
+    from mare, ass, and zebra, ii. 42;
+    of tame animals, wildness of, ii. 44-46;
+    female instincts of sterile male, ii. 52;
+    transmission and blending of characters in, ii. 92-95;
+    breed better with parent species than with each other, ii. 131;
+    self-impotence in, ii. 138-140;
+    readily produced in captivity, ii. 151.
+  HYBRIDISATION, singular effects of, in oranges, i. 336;
+    of cherries, i. 347;
+    difficulty of, in _Cucurbitae_, i. 358;
+    of roses, i. 366.
+  HYBRIDISM, ii. 178-191;
+    the cause of a tendency to double flowers, ii. 171;
+    in relation to pangenesis, ii. 385.
+  HYBRIDITY in cats, i. 44-45;
+    supposed of peach and nectarine, i. 342.
+  _Hydra_, i. 374, ii. 293, 359.
+  HYDRANGEA, colour of flowers of, influenced by alum, ii. 277.
+  HYDROCELE, ii. 52.
+  HYDROCEPHALUS, ii. 295.
+  _Hypericum calycinum_, ii. 170.
+  _Hypericum crispum_, ii. 227, 337.
+  HYPERMETAMORPHOSIS, ii. 367.
+  HYPERMETROPIA, hereditary, ii. 8.
+
+  ICHTHYOPTERYGIA, number of digits in the, ii. 16.
+  _Ilex aquifolium_, ii. 19.
+  IMAGINATION, supposed effect of, on offspring, ii. 263.
+  _Imatophyllum miniatum_, bud-variation in, i. 385.
+  INCEST, abhorred by savages, ii. 123-124.
+  INCUBATION, by crossed fowls of non-sitting varieties, ii. 43-44.
+  INDIA, striped horses of, i. 58;
+    pigs of, i. 66, 67, 76;
+    breeding of rabbits in, i. 112;
+    cultivation of pigeons in, i. 205-206.
+  INDIVIDUAL variability in pigeons, i. 158-160.
+  INGLEDEW, Mr., cultivation of European vegetables in India, ii. 169.
+  "INDISCHE Taube," ii. 144.
+  INHERITANCE, ii. 1-84, 371-373, 395, 397-402;
+    doubts entertained of by some writers, ii. 3;
+    importance of to breeders, 3-4;
+    evidence of, derived from statistics of chances, 5;
+    of peculiarities in man, 5-7, 12-16;
+    of disease, 7-8, 17;
+    of peculiarities in the eye, 8-10;
+    of deviations from symmetry, 12;
+    of polydactylism, 12-16;
+    capriciousness of, 17-22, 27;
+    of mutilations, 22-24;
+    of congenital monstrosities, 24;
+    causes of absence of, 24-26;
+    by reversion or atavism, 28-61;
+    its connexion with fixedness of character, 62-64;
+    affected by prepotency of transmission of character, 65-71;
+    limited by sex, 71-75;
+    at corresponding periods of life, 75-80;
+    summary of the subject of, 80-84;
+    laws of, the same in seminal and bud varieties, i. 409;
+    of characters in the horse, i. 10-11;
+    in cattle, i. 87;
+    in rabbits, i. 107;
+    in the peach, i. 339;
+    in the nectarine, i. 340;
+    in plums, i. 347;
+    in apples, i. 350;
+    in pears, i. 351;
+    in the pansy, i. 369;
+    of primary characters of _Columba livia_ in crossed pigeons, i. 201;
+    of peculiarities of plumage in pigeons, i. 160-161;
+    of peculiarities of foliage in trees, i. 362;
+    effects of, in varieties of the cabbage, i. 325.
+  INSANITY, inheritance of, ii. 7, 78.
+  INSECTS, regeneration of lost parts in, ii. 15, 294;
+    agency of, in fecundation of larkspurs, ii. 21;
+    effect of changed conditions upon, ii. 157;
+    sterile neuter, ii. 186-187;
+  {459}
+    monstrosities in, ii. 269, 391.
+  INSTINCTS, defective, of silkworms, i. 304.
+  INTERBREEDING, close, ill effects of, ii. 114-131, 175.
+  INTERCROSSING, of species, as a cause of variation, i. 188;
+    natural, of plants, i. 336;
+    of species of Canidae and breeds of dogs, i. 31-33;
+    of domestic and wild cats, i. 44-45;
+    of breeds of pigs, i. 71, 78;
+    of cattle, i. 83;
+    of varieties of cabbage, i. 324;
+    of peas, i. 326, 329-330;
+    of varieties of orange, i. 336;
+    of species of strawberries, i. 351-352;
+    of _Cucurbitae_, i. 357-358;
+    of flowering plants, i. 364;
+    of pansies, i. 368.
+  INTERDIGITAL pits, in goats, i. 102.
+  INTERMARRIAGES, close, ii. 122-123.
+  INTESTINES, elongation of, in pigs, i. 73;
+    relative measurements of parts of, in goats, i. 102;
+    effects of changed diet on, ii. 302.
+  _Ipomoea purpurea_, ii. 128.
+  IRELAND, remains of _Bos frontosus_ and _longifrons_ found in, i. 81.
+  IRIS, hereditary absence of the, ii. 9;
+    hereditary peculiarities of colour of the, ii. 9-10.
+  IRISH, ancient, selection practised by the, ii. 203.
+  IRON period, in Europe, dog of, i. 18.
+  ISLANDS, oceanic, scarcity of useful plants on, i. 311.
+  ISLAY, pigeons of, i. 183.
+  ISOLATION, effect of, in favour of selection, ii. 233-234.
+  ITALY, vine growing in, during the bronze period, i. 332.
+  IVY, sterility of, in the north of Europe, ii. 170.
+
+  JACK, Mr., effect of foreign pollen on grapes, i. 400.
+  JACKAL, i. 24, 27, 30;
+    hybrids of, with the dog, i. 32;
+    prepotency of, over the dog, ii. 67.
+  JACOBIN pigeon, i. 154, 208.
+  JACQUEMET-BONNEFORT, on the mulberry, i. 334.
+  JAGUAR, with crooked legs, i. 17.
+  JAMAICA, feral dogs of, i. 28;
+    feral pigs of, i. 77;
+    feral rabbits of, i. 112.
+  JAPAN, horses of, i. 53.
+  JAPANESE pig (figured), i. 69.
+  JARDINE, Sir W., crossing of domestic and wild cats, i. 44.
+  JARVES, J., silkworm in the Sandwich islands, i. 301.
+  JAVA, Fantail pigeon in, i. 148.
+  JAVANESE ponies, i. 53, 59.
+  JEMMY BUTTON, i. 309.
+  JENYNS, L., whiteness of ganders, i. 288;
+    sunfish-like variety of the goldfish, i. 297.
+  JERDON, J. C., number of eggs laid by the pea-hen, ii. 112;
+    origin of domestic fowl, i. 237.
+  JERSEY, arborescent cabbages of, i. 323.
+  JESSAMINE, i. 394.
+  JEITTELES, Hungarian sheep-dogs, i. 24;
+    crossing of domestic and wild cats, i. 44.
+  JOHN, King, importation of stallions from Flanders by, ii. 203.
+  JOHNSON, D., occurrence of stripes on young wild pigs in India, i. 76.
+  JORDAN, A., on Vibert's experiments on the vine, i. 332;
+    origin of varieties of the apple, i. 350;
+    varieties of pears found wild in woods, ii. 260.
+  JOURDAN, parthenogenesis in the silk moth, ii. 364.
+  JUAN DE NOVA, wild dogs on, i. 27.
+  JUAN FERNANDEZ, dumb dogs on, i. 27.
+  _Juglans regia_, i. 356-357.
+  JUKES, Prof., origin of the Newfoundland dog, i. 42.
+  JULIEN, Stanislas, early domestication of pigs in China, i. 68;
+    antiquity of the domestication of the silk-worm in China, i. 300.
+  JUMPERS, a breed of fowls, i. 230.
+  JUNIPER, variations of the, i. 361, 364.
+  _Juniperus suecica_, i. 361.
+  _Jussiaea grandiflora_, ii. 170.
+  JUSSIEU, A. de, structure of the pappus in _Carthamus_, ii. 316.
+
+  KAIL, Scotch, reversion in, ii. 32.
+  "KALA-PAR" pigeon, i. 142.
+  KALES, i. 323.
+  KALM, P., on maize, i. 322, ii. 307;
+    introduction of wheat into Canada, i. 315;
+    sterility of trees growing in marshes and dense woods, ii. 170.
+  "KALMI Lotan," tumbler pigeon, i. 151.
+  KANE, Dr., on Esquimaux dogs, i. 21.
+  KARAKOOL sheep, i. 98.
+  KARKEEK, on inheritance in the horse, ii. 10.
+  "KARMELITEN Taube," i. 156.
+  KARSTEN on _Pulex penetrans_, ii. 275.
+  KATTYWAR horses, i. 58.
+  KEELEY, R., pelorism in _Galeobdolon luteum_, ii. 59.
+  KERNER on the culture of Alpine plants, ii. 163.
+  KESTREL, breeding in captivity, ii. 154.
+  "KHANDESI," i. 141.
+  KHANG-HI, selection of a variety of rice by, ii. 205.
+  KIANG, ii. 43.
+  KIDD, on the canary bird, i. 77, ii. 275.
+  KIDNEY Bean, i. 371;
+    varieties of, ii. 256, 275.
+  {460}
+  KIDNEYS, compensatory development of the, ii. 300;
+    fusion of the, ii. 341;
+    shape of, in birds, influenced by the form of the pelvis, ii. 344.
+  KING, Col., domestication of rock doves from the Orkneys, i. 184, 185.
+  KING, P. S., on the Dingo, i. 21, 28.
+  KIRBY and Spence, on the growth of galls, ii. 283.
+  KIRGHISIAN sheep, i. 98.
+  KITE, breeding in captivity, ii. 154.
+  KLEINE, variability of bees, i. 298.
+  KNIGHT, Andrew, on crossing horses of different breeds, i. 51;
+    crossing varieties of peas, i. 326, ii. 129;
+    persistency of varieties of peas, i. 329;
+    origin of the peach, i. 338;
+    hybridisation of the morello by the Elton cherry, i. 347;
+    on seedling cherries, _ibid._;
+    variety of the apple not attacked by coccus, i. 349;
+    intercrossing of strawberries, i, 351, 352;
+    broad variety of the cock's comb, i. 365;
+    bud variation in the cherry and plum, i. 375;
+    crossing of white and purple grapes, i. 393;
+    experiments in crossing apples, i. 402, ii. 129;
+    hereditary disease in plants, ii. 11;
+    on interbreeding, ii. 116;
+    crossed varieties of wheat, ii. 130;
+    necessity of intercrossing in plants, ii. 175;
+    on variation, ii. 256, 257;
+    effects of grafting, i. 387, ii. 278;
+    bud-variation in a plum, ii. 289;
+    compulsory flowering of early potatoes, ii. 343;
+    correlated variation of head and limbs, ii. 323.
+  KNOX, Mr., breeding of the eagle owl in captivity, ii. 154.
+  KOCH, degeneracy in the turnip, i. 325.
+  KOHLRABI, i. 323.
+  KOELREUTER, reversion in hybrids, i. 392, ii. 36;
+    acquired sterility of crossed varieties of plants, i. 358, ii. 101;
+    absorption of _Mirabilis vulgaris_ by _M. longiflora_, ii. 88;
+    crosses of species of _Verbascum_, ii. 93, 107;
+    on the hollyhock, ii. 107;
+    crossing varieties of tobacco, ii. 108;
+    benefits of crossing plants, ii. 130, 131, 175-176;
+    self-impotence in _Verbascum_, ii. 136, 141;
+    effects of conditions of growth upon fertility in _Mirabilis_, ii. 164;
+    great development of tubers in hybrid plants, ii. 172;
+    inheritance of plasticity, ii. 241;
+    variability of hybrids of _Mirabilis_, ii. 265;
+    repeated crossing a cause of variation, ii. 267-268;
+    number of pollen-grains necessary for fertilization, ii. 363.
+  "KRAUSESCHWEIN," i. 67.
+  KROHN, on the double reproduction of Medusae, ii. 384.
+  "KROPF-TAUBEN," i. 137.
+
+  LABAT, on the tusks of feral bears in the West Indies, i. 77;
+    on French wheat grown in the West Indies, ii. 307;
+    on the culture of the vine in the West Indies, ii. 308.
+  LABURNUM, Adam's, see _Cytisus Adami_;
+    oak-leaved, reversion of, i. 382;
+    pelorism in the, ii. 346;
+    Waterer's, i. 390.
+  LACHMANN, on gemmation and fission, ii. 358.
+  _Lachnanthes tinctoria_, ii. 227, 336.
+  LACTATION, imperfect, hereditary, ii. 8;
+    deficient, of wild animals in captivity, ii. 158.
+  LADRONE islands, cattle of, i. 86.
+  LAING, Mr., resemblance of Norwegian and Devonshire cattle, i. 82.
+  LAKE-DWELLINGS, sheep of, i. 94, ii. 427;
+    cattle of, ii. 427;
+    absence of the fowl in, i. 246;
+    cultivated plants of, i. 309, ii. 427, 429;
+    cereals of, i. 317-319;
+    peas found in, i. 326;
+    beans found in, i. 330.
+  LAMARE-PIQUOT, observations on half-bred North American wolves, i. 22.
+  LAMBERT, A. B., on _Thuja pendula_ or _filiformis_, i. 362.
+  LAMBERT family, ii. 4, 76.
+  LAMBERTYE on strawberries, i. 351, 352;
+    five-leaved variety of _Fragaria collina_, i. 353.
+  LANDT, L., on sheep in the Faroe islands, ii. 103.
+  LA PLATA, wild dogs of, i. 27;
+    feral cat from, i. 47.
+  LARCH, ii. 310.
+  LARKSPURS, insect agency necessary for the full fecundation of, ii. 21.
+  _Larus argentatus_, ii. 157.
+  _Larus tridactylus_, ii. 302.
+  LASTERYE, merino sheep in different countries, i. 99.
+  LATENT characters, ii. 51-56.
+  LATHAM, on the fowl not breeding in the extreme north, ii. 161.
+  _Lathyrus_, ii. 38.
+  _Lathyrus aphaca_, ii. 343.
+  _Lathyrus odoratus_, ii. 20, 91, 93, 311, 393.
+  LA TOUCHE, J. D., on a Canadian apple with dimidiate fruit, i. 392-393.
+  "LATZ-TAUBE," i. 154.
+  LAUGHER pigeon, i. 155, 207.
+  _Laurus sassafras_, ii. 274.
+  LAWRENCE, J., production of a new breed of fox-hounds, i. 40;
+    occurrence of canines in mares, i. 50;
+    on three-parts-bred horses, i. 54;
+    on inheritance in the horse, ii. 10-11.
+  LAWSON, Mr., varieties of the potato, i. 330.
+  LAXTON, Mr., bud-variation in the gooseberry, i. 376;
+    crossing of varieties of the pea, i. 397-398;
+  {461}
+    double-flowered peas, ii. 168.
+  LAYARD, E. L., resemblance of a Caffre dog to the Esquimaux breed, i. 25,
+      ii. 286;
+    crossing of the domestic cat with _Felis Caffra_, i. 44;
+    feral pigeons in Ascension, i. 190;
+    domestic pigeons of Ceylon, i. 206;
+    on _Gallus Stanleyi_, i. 234;
+    on black-skinned Ceylonese fowls, i. 256.
+  LE COMPTE family, blindness inherited in, ii. 78.
+  LECOQ, bud-variation in _Mirabilis jalapa_, i. 382;
+    hybrids of _Mirabilis_, i. 393, ii. 169, 265;
+    crossing in plants, ii. 127;
+    fecundation of _Passiflora_, ii. 137;
+    hybrid _Gladiolus_, ii. 139;
+    sterility of _Ranunculus ficaria_, ii. 170;
+    villosity in plants, ii. 277;
+    double asters, ii. 316.
+  LE COUTEUR, J., varieties of wheat, i. 313-315;
+    acclimatisation of exotic wheat in Europe, i. 315;
+    adaptation of wheat to soil and climate, i. 316;
+    selection of seed-corn, i. 318;
+    on change of soil, ii. 147;
+    selection of wheat, ii. 200;
+    natural selection in wheat, ii. 233;
+    cattle of Jersey, ii. 234.
+  LEDGER, Mr., on the Llama and Alpaca, ii. 208.
+  LEE, Mr., his early culture of the pansy, i. 368.
+  _Leersia oryzoides_, ii. 91.
+  LEFOUR, period of gestation in cattle, i. 87.
+  LEGS, of fowls, effects of disuse on, i. 270-272;
+    characters and variations of, in ducks, i. 284-288;
+    fusion of, ii. 341.
+  LEGUAT, cattle of the Cape of Good Hope, i. 88.
+  LEHMANN, occurrence of wild double-flowered plants near a hot spring, ii.
+      168.
+  LEIGHTON, W. A., propagation of a weeping yew by seed, ii. 19.
+  LEITNER, effects of the removal of anthers, ii. 167.
+  LEMMING, ii. 152.
+  LEMOINE, variegated _Symphytum_ and _Phlox_, i. 384.
+  LEMON, i. 334, 335;
+    orange fecundated by pollen of the, i. 399.
+  LEMURS, hybrid, ii. 153.
+  LEPORIDES, ii. 98-99, 152.
+  LEPSIUS, figures of ancient Egyptian dogs, i. 17;
+    domestication of pigeons in ancient Egypt, i. 204.
+  _Leptotes_, ii. 134.
+  _Lepus glacialis_, i. 111.
+  _Lepus magellanicus_, i. 112.
+  _Lepus nigripes_, i. 108.
+  _Lepus tibetanus_, i. 111.
+  _Lepus variabilis_, i. 111.
+  LEREBOULLET, double monsters of fishes, ii. 340.
+  LESLIE, on Scotch wild cattle, i. 85.
+  LESSON, on _Lepus magellanicus_, i. 112.
+  LEUCKART on the larva of Cecidomyidae, ii. 360.
+  LEWIS, G., cattle of the West Indies, ii. 229.
+  LHERBETTE and Quatrefages, on the horses of Circassia, ii. 102, 225.
+  LIEBIG, differences in human blood, according to complexion, ii. 276.
+  LIEBREICH, occurrence of pigmentary retinitis in deaf-mutes, ii. 328.
+  LICHENS, sterility in, ii. 171.
+  LICHTENSTEIN, resemblance of Bosjesman's dogs to _Canis mesomelas_, i.
+      25;
+    Newfoundland dog at the Cape of Good Hope, i. 36.
+  LILACS, ii. 164.
+  LILIACEAE, contabescence in, ii. 165.
+  _Lilium candidum_, ii. 137.
+  LIMBS, regeneration of, ii. 376-377.
+  LIMBS and head, correlated variation of, ii. 323.
+  LIME, effect of, upon shells of the mollusca, ii. 280.
+  LIME tree, changes of by age, i. 364, 387.
+  LIMITATION, sexual, ii. 71-75.
+  LIMITATION, supposed, of variation, ii. 416.
+  _Linaria_, pelorism in, ii. 58, 61, 346;
+    peloric, crossed with the normal form, ii. 70;
+    sterility of, ii. 166.
+  _Linaria vulgaris_ and _purpurea_, hybrids of, ii. 94.
+  LINDLEY, John, classification of varieties of cabbages, i. 324;
+    origin of the peach, i. 338;
+    influence of soil on peaches and nectarines, i. 340;
+    varieties of the peach and nectarine, i. 343;
+    on the New Town pippin, i. 349;
+    freedom of the Winter Majetin apple from coccus, i. 349;
+    production of monoecious Hautbois strawberries by bud-selection, i.
+        353;
+    origin of the large tawny nectarine, i. 375;
+    bud-variation in the gooseberry, i. 376;
+    hereditary disease in plants, ii. 11;
+    on double flowers, ii. 167;
+    seeding of ordinarily seedless fruits, ii. 168;
+    sterility of _Acorus calamus_, ii. 170;
+    resistance of individual plants to cold, ii. 309.
+  LINNAEUS, summer and winter wheat regarded as distinct species by, i.
+      315;
+    on the single-leaved strawberry, i. 353;
+    sterility of Alpine plants in gardens, ii. 163;
+    recognition of individual reindeer by the Laplanders, ii. 251;
+    growth of tobacco in Sweden, ii. 307.
+  LINNET, ii. 158.
+  _Linota cannabina_, ii. 158.
+  {462}
+  LINUM, ii. 165.
+  LION, fertility of, in captivity, ii. 150, 151.
+  LIPARI, feral rabbits of, i. 113.
+  LIVINGSTONE, Dr., striped young pigs on the Zambesi, i. 77;
+    domestic rabbits at Loanda, i. 112;
+    use of grass-seeds as food in Africa, i. 308;
+    planting of fruit-trees by the Batokas, i. 309;
+    character of half-castes, ii. 46;
+    taming of animals among the Barotse, ii. 160;
+    selection practised in South Africa, ii. 207, 209.
+  LIVINGSTONE, Mr., disuse a cause of drooping ears, ii. 301.
+  LIZARDS, reproduction of tail in, ii. 294;
+    with a double tail, ii. 341.
+  LLAMA, selection of, ii. 208.
+  LLOYD, Mr., taming of the wolf, i. 26;
+    English dogs in northern Europe, i. 36;
+    fertility of the goose increased by domestication, i. 288;
+    number of eggs laid by the wild goose, ii. 112;
+    breeding of the capercailzie in captivity, ii. 156.
+  LOANDA, domestic rabbits at, i. 112.
+  _Loasa_, hybrid of two species of, ii. 98.
+  _Lobelia_, reversion in hybrids of, ii. 392;
+    contabescence in, ii. 166.
+  _Lobelia fulgens_, _cardinalis_, and _syphilitica_, ii. 136.
+  LOCKHART, Dr., on Chinese pigeons, i. 206.
+  LOCUST-TREE, ii. 274.
+  LOISELEUR-DESLONGCHAMPS, originals of cultivated plants, i. 307;
+    Mongolian varieties of wheat, i. 313;
+    characters of the ear in wheat, i. 314;
+    acclimatisation of exotic wheat in Europe, i. 315;
+    effect of change of climate on wheat, i. 316;
+    on the supposed necessity of the coincident variation of weeds and
+        cultivated plants, i. 317;
+    advantage of change of soil to plants, ii. 146.
+  _Lolium temulentum_, variable presence of barbs in, i. 314.
+  LONG-TAILED sheep, i. 94, 95.
+  LOOCHOO islands, horses of, i. 53.
+  LORD, J. K., on Canis latrans, i. 22.
+  "LORI RAJAH," how produced, ii. 280.
+  _Lorius garrulus_, ii. 280.
+  "LOTAN," tumbler pigeon, i. 150.
+  LOUDON, J. W., varieties of the carrot, i. 326;
+    short duration of varieties of peas, i. 329;
+    on the glands of peach-leaves, i. 343;
+    presence of bloom on Russian apples, i. 349;
+    origin of varieties of the apple, i. 350;
+    varieties of the gooseberry, i. 354;
+    on the nut tree, i. 357;
+    varieties of the ash, i. 360;
+    fastigate juniper (_J. suecica_), i. 361;
+    on _Ilex aquifolium ferox_, i. 362;
+    varieties of the Scotch fir, i. 363;
+    varieties of the hawthorn, _ibid._;
+    variation in the persistency of leaves on the elm and Turkish oak, i.
+        363;
+    importance of cultivated varieties, _ibid._;
+    varieties of _Rosa spinosissima_, i. 367;
+    variation of dahlias from the same seed, i. 370;
+    production of Provence roses from seeds of the moss rose, i. 380;
+    effect of grafting the purple-leaved upon the common hazel, i. 395;
+    nearly evergreen Cornish variety of the elm, ii. 310.
+  LOW, G., on the pigs of the Orkney islands, i. 70.
+  LOW, Prof., pedigrees of greyhounds, ii. 3;
+    origin of the dog, i. 10;
+    burrowing instinct of a half-bred Dingo, i. 28;
+    inheritance of qualities in horses, i. 51;
+    comparative powers of English race-horses, Arabs, &c., i. 54;
+    British breeds of cattle, i. 80;
+    wild cattle of Chartley, i. 84;
+    effect of abundance of food on the size of cattle, i. 91;
+    effects of climate on the skin of cattle, i. 92, ii. 326;
+    on interbreeding, ii. 116;
+    selection in Hereford cattle, ii. 214;
+    formation of new breeds, ii. 244;
+    on "sheeted" cattle, ii. 349.
+  LOWE, Mr., on hive bees, i. 299.
+  LOWE, REV. Mr., on the range of _Pyrus malus_ and _P. acerba_, i. 348.
+  "LOWTAN" tumbler pigeon, i. 150.
+  _Loxia pyrrhula_, ii. 154.
+  LUBBOCK, Sir J., developments of the Ephemeridae, ii. 366.
+  LUCAS, P., effects of cross-breeding on the female, i. 404;
+    hereditary diseases, ii. 7, 78-79;
+    hereditary affections of the eye, ii. 9-10;
+    inheritance of anomalies in the human eye and in that of the horse, ii.
+        10, 11;
+    inheritance of polydactylism, ii. 13;
+    morbid uniformity in the same family, ii. 17;
+    inheritance of mutilations, ii. 23;
+    persistency of cross-reversion, ii. 35;
+    persistency of character in breeds of animals in wild countries, ii.
+        64;
+    prepotency of transmission, ii. 65, 68;
+    supposed rules of transmission in crossing animals, ii. 68;
+    sexual limitations of transmission of peculiarities, ii. 72-73;
+    absorption of the minority in crossed races, ii. 88;
+    crosses without blending of certain characters, ii. 92;
+    on interbreeding, ii. 116;
+    variability dependent on reproduction, ii. 250;
+    period of action of variability, ii. 260;
+    inheritance of deafness in cats, ii. 329;
+    complexion and constitution, ii. 335.
+  LUCAZE-DUTHIERS, structure and growth of galls, ii. 282-284.
+  LUIZET, grafting of a peach-almond on a peach, i. 338.
+  {463}
+  LUETKE, cats of the Caroline Archipelago, i. 47.
+  LUXURIANCE, of vegetative organs, a cause of sterility in plants, ii.
+      168-171.
+  LYONNET, on the scission of _Nais_, ii. 358.
+  _Lysimachia nummularia_, sterility of, ii. 170.
+  _Lythrum_, trimorphic species of, ii. 400.
+  _Lythrum salicaria_, ii. 183;
+    contabescence in, ii. 166.
+  _Lytta vesicatoria_, affecting the kidneys, ii. 380.
+
+  _Macacus_, species of, bred in captivity, ii. 153.
+  MACAULAY, Lord, improvement of the English horse, ii. 213.
+  MCCLELLAND, Dr., variability of fresh-water fishes in India, ii. 259.
+  MCCOY, Prof., on the dingo, i. 26.
+  MACFAYDEN, influence of soil in producing sweet or bitter oranges from
+      the same seed, i. 335.
+  MACGILLIVRAY, domestication of the rock-dove, i. 185;
+    feral pigeons in Scotland, i. 190;
+    number of vertebrae in birds, i. 266;
+    on wild geese, i. 287;
+    number of eggs of wild and tame ducks, ii. 112.
+  MACKENZIE, Sir G., peculiar variety of the potato, i. 330.
+  MACKENZIE, P., bud-variation in the currant, i. 376.
+  MACKINNON, Mr., horses of the Falkland islands, i. 52;
+    feral cattle of the Falkland islands, i. 86.
+  MACKNIGHT, C., on interbreeding cattle, ii. 118.
+  MACNAB, Mr., on seedling weeping birches, ii. 18;
+    non-production of the weeping beech by seed, ii. 19.
+  MADAGASCAR, cats of, i. 47.
+  MADDEN, H., on interbreeding cattle, ii. 118.
+  MADEIRA, rock pigeon of, i. 184.
+  _Magnolia grandiflora_, ii. 308.
+  MAIZE, its unity of origin, i. 320;
+    antiquity of, _ibid._;
+    with husked grains said to grow wild, _ibid._;
+    variation of, i. 321;
+    irregularities in the flowers of, i. 321;
+    persistence of varieties, _ibid._;
+    adaptation of to climate, i. 322, ii. 307;
+    acclimatisation of, ii. 313, 347;
+    crossing of, i. 400, ii. 104-105;
+    extinct Peruvian varieties of, ii. 425.
+  MALAY fowl, i. 227.
+  MALAY Archipelago, horses of, i. 53;
+    short-tailed cats of, i. 47;
+    striped young wild pigs of, i. 76;
+    ducks of, i. 280.
+  MALE, influence of, on the fecundated female, i. 397-406;
+    supposed influence of, on offspring, ii. 68.
+  MALE flowers, appearance of, among female flowers in maize, i. 321.
+  MALFORMATIONS, hereditary, ii. 79.
+  _Malva_, fertilisation of, i. 402, ii. 363.
+  _Mamestra suasa_, ii. 157.
+  MAMMAE, variable in number in the pig, i. 74;
+    rudimentary, occasional full development of, in cows, i. 87, ii. 317;
+    four present in some sheep, i. 95;
+    variable in number in rabbits, i. 106;
+    latent functions of, in male animals, ii. 52, 317;
+    supernumerary and inguinal, in women, ii. 57.
+  MANGLES, Mr., annual varieties of the heartsease, ii. 305.
+  MANTELL, Mr., taming of birds by the New Zealanders, ii. 161.
+  MANU, domestic fowl noticed in the Institutes of, i. 246.
+  MANURE, effect of, on the fertility of plants, ii. 163.
+  MANX cats, i. 46, ii. 66.
+  MARCEL de Serres, fertility of the ostrich, ii. 156.
+  MARIANNE islands, varieties of _Pandanus_ in, ii. 256.
+  MARKHAM, Gervase, on rabbits, i. 104, ii. 204.
+  MARKHOR, probably one of the parents of the goat, i. 101.
+  MARQUAND, cattle of the channel islands, i. 80.
+  MARRIMPOEY, inheritance in the horse, ii. 10.
+  MARROW, vegetable, i. 357.
+  MARRYATT, Capt., breeding of asses in Kentucky, ii. 237.
+  MARSDEN, notice of _Gallus giganteus_, i. 235.
+  MARSHALL, Mr., voluntary selection of pasture by sheep, i. 96;
+    adaptation of wheats to soil and climate, i. 316;
+    "Dutch-buttocked" cattle, ii. 8;
+    segregation of herds of sheep, ii. 103;
+    advantage of change of soil to wheat and potatoes, ii. 146;
+    fashionable change in the horns of cattle, ii. 210;
+    sheep in Yorkshire, ii. 235.
+  MARSHALL, Prof., growth of the brain in microcephalous idiots, ii. 389.
+  MARTENS, E. Von, on _Achatinella_, ii. 53.
+  MARTIN, W. C. L., origin of the dog, i. 16;
+    Egyptian dogs, i. 18;
+    barking of a Mackenzie River dog, i. 27;
+    African hounds in the Tower menagerie, i. 32;
+    on dun horses and dappled asses, i. 55;
+    breeds of the horse, i. 49;
+    wild horses, i. 51;
+    Syrian breeds of asses, i. 62;
+    asses without stripes, i. 63;
+    effects of cross-breeding on the female in dogs, i. 404;
+    striped legs of mules, ii. 42.
+  MARTINS, defective instincts of silkworms, i. 304.
+  MARTINS, C., fruit trees of Stockholm, ii. 307.
+  {464}
+  MASON, W., bud-variation in the ash, i. 382.
+  MASTERS, Dr., reversion in the spiral-leaved weeping willow, i. 383;
+    on peloric flowers, ii. 58;
+    pelorism in a clover, ii. 346;
+    position as a cause of pelorism, ii. 345, 347.
+  MASTERS, Mr., persistence of varieties of peas, i. 329;
+    reproduction of colour in hyacinths, ii. 20;
+    on hollyhocks, ii. 107;
+    selection of peas for seed, ii. 199-200;
+    on _Opuntia leucotricha_, ii. 286;
+    reversion by the terminal pea in the pod, ii. 347.
+  MASTIFF, sculptured on an Assyrian monument, i. 17, ii. 429;
+    Tibetan, i. 35-36, ii. 278.
+  MATTHEWS, Patrick, on forest trees, ii. 237.
+  _Matthiola annua_, i. 399, ii. 20.
+  _Matthiola incana_, i. 381, 399.
+  MAUCHAMP, merino sheep, i. 100.
+  MAUDUYT, crossing of wolves and dogs in the Pyrenees, i. 24.
+  MAUND, Mr. crossed varieties of wheat, ii. 130.
+  MAUPERTUIS, axiom of "least action," i. 12.
+  MAURITIUS, importation of goats into, i. 101.
+  MAW, G., correlation of contracted leaves and flowers in pelargoniums,
+      ii. 330, 331.
+  MAWZ, fertility of _Brassica rapa_, ii. 165.
+  _Maxillaria_, self-fertilised capsules of, ii. 134;
+    number of seeds in, ii. 379.
+  _Maxillaria atro-rubens_, fertilisation of, by _M. squalens_, ii. 133.
+  MAYES, M., self-impotence in _Amaryllis_, ii. 139.
+  MECKEL, on the number of digits, ii. 13;
+    correlation of abnormal muscles in the leg and arm, ii. 322.
+  MEDUSAE, development of, ii. 368, 384.
+  MEEHAN, Mr., comparison of European and American trees, ii. 281.
+  _Meleagris mexicana_, i. 292.
+  _Meles taxus_, ii. 151.
+  MELONS, i. 359-360;
+    mongrel, supposed to be produced from a twin-seed, i. 391;
+    crossing of varieties of, i. 399, ii. 108, 129;
+    inferiority of, in Roman times, ii. 216;
+    changes in, by culture and climate, ii. 275;
+    serpent, correlation of variations in, ii. 330;
+    analogous variations in, ii. 349.
+  MEMBRANES, false, ii. 294-295.
+  MENETRIES, on the stomach of _Strix grallaria_, ii. 302.
+  MENINGITIS, tubercular, inherited, ii. 78.
+  METAGENESIS, ii. 366.
+  METAMORPHOSIS, ii. 366.
+  METAMORPHOSIS and development, ii. 388, 389.
+  METZGER, on the supposed species of wheat, i. 312-313;
+    tendency of wheat to vary, i. 315;
+    variation of maize, i. 321-322;
+    cultivation of American maize in Europe, i. 322, ii. 347;
+    on cabbages, i. 323-325;
+    acclimatisation of Spanish wheat in Germany, ii. 26;
+    advantage of change of soil to plants, ii. 146;
+    on rye, ii. 254;
+    cultivation of different kinds of wheat, ii. 261.
+  MEXICO, dog from, with tan spots on the eyes, i. 29;
+    colours of feral horses in, i. 61.
+  MEYEN, on sending of bananas, ii. 168.
+  MICE, grey and white, colours of, not blended by crossing, ii. 92;
+    rejection of bitter almonds by, ii. 232;
+    naked, ii. 279.
+  MICHAUX, F., roan-coloured feral horses of Mexico, i. 61;
+    origin of domestic turkey, i. 292;
+    on raising peaches from seed, i. 339.
+  MICHEL, F., selection of horses in mediaeval times, ii. 203;
+    horses preferred on account of slight characters, ii. 209.
+  MICHELY, effects of food on caterpillars, ii. 280;
+    on _Bombyx hesperus_, ii. 304.
+  MICROPHTHALMIA, associated with defective teeth, ii. 328.
+  MIDDENS, Danish, remains of dogs in, i. 18, ii. 427.
+  MIGNONETTE, ii. 237, 311.
+  MILLET, i. 371.
+  MILLS, J., diminished fertility of mares when first turned out to grass,
+      ii. 161.
+  MILNE-EDWARDS, on the development of the crustacea, ii. 368.
+  MILNE-EDWARDS, A., on a crustacean with a monstrous eye-peduncle, ii.
+      391.
+  _Milvus niger_, ii. 154.
+  _Mimulus luteus_, ii. 128.
+  MINOR, W. C., gemmation and fission in the Annelida, ii. 358.
+  _Mirabilis_, fertilisation of, ii. 363;
+    hybrids of, ii. 131, 169, 265.
+  _Mirabilis jalapa_, i. 382, 393.
+  _Mirabilis longiflora_, ii. 88.
+  _Mirabilis vulgaris_, ii. 88.
+  _Misocampus_ and _Cecidomyia_, i. 5.
+  MITCHELL, Dr., effects of the poison of the rattlesnake, ii. 289.
+  MITFORD, Mr., notice of the breeding of horses by Erichthonius, ii. 202.
+  MOCCAS Court, weeping oak at, ii. 18.
+  MOGFORD, horses poisoned by fool's parsley, ii. 337.
+  MOELLER, L., effects of food on insects, ii. 281.
+  MOQUIN-TANDON, original form of maize, i. 320;
+    variety of the double columbine, i. 365;
+  {465}
+    peloric flowers, ii. 58-59, 61;
+    position as a cause of pelorism in flowers, ii. 345;
+    tendency of peloric flowers to become irregular, ii. 70;
+    on monstrosities, ii. 254;
+    correlation in the axis and appendages of plants, ii. 321;
+    fusion of homologous parts in plants, ii. 339, 341-342;
+    on a bean with monstrous stipules and abortive leaflets, ii. 343;
+    conversion of parts of flowers, ii. 392.
+  MOLE, white, ii. 332.
+  MOLL and Gayot, on cattle, i. 80, ii. 96, 210.
+  MOLLUSCA, change in shells of, ii. 280.
+  MONKE, Lady, culture of the pansy by, i. 368.
+  MONKEYS, rarely fertile in captivity, ii. 153.
+  MONNIER, identity of summer and winter wheat, i. 315.
+  MONSTER, cyclopean, ii. 341.
+  MONSTERS, double, ii. 339-340.
+  MONSTROSITIES, occurrence of, in domesticated animals and cultivated
+      plants, i. 366, ii. 254;
+    due to persistence of embryonic conditions, ii. 57;
+    occurring by reversion, ii. 57-60;
+    a cause of sterility, ii. 166-167;
+    caused by injury to the embryo, ii. 269.
+  MONTEGAZZA, growth of a cock's-spur inserted into the eye of an ox, ii.
+      369.
+  MONTGOMERY, E., formation of cells, ii. 370.
+  MOOR, J. H., deterioration of the horse in Malasia, i. 53.
+  MOORCROFT, Mr., on Hasora wheat, i. 313;
+    selection of white-tailed yaks, ii. 206;
+    melon of Kaschmir, ii. 275;
+    varieties of the apricot cultivated in Ladakh, i. 345;
+    varieties of the walnut cultivated in Kaschmir, i. 356.
+  MOORE, Mr., on breeds of pigeons, i. 148, 156, 208, 209, 211.
+  MOORUK, fertility of, in captivity, ii. 156.
+  MORLOT, dogs of the Danish Middens, i. 18;
+    sheep and horse of the bronze period, ii. 427.
+  _Mormodes ignea_, ii. 53.
+  MOROCCO, estimation of pigeons in, i. 205.
+  MORREN, C., on pelorism, ii. 58;
+    in _Calceolaria_, ii. 346;
+    non-coincidence of double flowers and variegated leaves, ii. 167.
+  MORRIS, Mr., breeding of the Kestrel in captivity, ii. 154.
+  MORTON, Lord, effect of fecundation by a quagga on an Arab mare, i.
+      403-404.
+  MORTON, Dr., origin of the dog, i. 16;
+    hybrid of zebra and mare, ii. 42.
+  _Morus alba_, i. 334.
+  MOSCOW, rabbits of, i. 106, 120;
+    effects of cold on pear-trees at, ii. 307.
+  MOSSES, sterility in, ii. 171;
+    retrogressive metamorphosis in, ii. 361.
+  MOSS-ROSE, probable origin of, from _Rosa centifolia_, i. 379;
+    Provence roses produced from seeds of, i. 380.
+  MOSTO, Cada, on the introduction of rabbits into Porto Santo, i. 113.
+  MOTTLING of fruits and flowers, i. 400.
+  MOUFFLON, i. 94.
+  MOUNTAIN-ASH, ii. 230.
+  MOUSE, Barbary, ii. 152.
+  "MOEVEN-TAUBE," i. 148.
+  MOWBRAY, Mr., on the eggs of game fowls, i. 248;
+    early pugnacity of game cocks, i. 251;
+    diminished fecundity of the pheasant in captivity, ii. 155.
+  MOWBRAY, Mr., reciprocal fecundation of _Passiflora alata_ and
+      _racemosa_, ii. 137.
+  MULATTOS, character of, ii. 46.
+  MULBERRY, i. 334, ii. 256.
+  MULE and hinny, differences in the, ii. 67-68.
+  MULES, striped colouring of, ii. 42;
+    obstinacy of, ii. 45;
+    production of, among the Romans, ii. 110;
+    noticed in the Bible, ii. 202.
+  MUELLER, Fritz, reproduction of orchids, ii. 134-135;
+    development of crustacea, ii. 368;
+    number of seeds in a _maxillaria_, ii. 379.
+  MUELLER, H., on the face and teeth in dogs, i. 34, 73, ii. 345.
+  MUELLER, J., production of imperfect nails after partial amputation of
+      the fingers, ii. 15;
+    tendency to variation, ii. 252;
+    atrophy of the optic nerve consequent on destruction of the eye, ii.
+        297;
+    on Janus-like monsters, ii. 340;
+    on gemmation and fission, ii. 358;
+    identity of ovules and buds, ii. 360;
+    special affinities of the tissues, ii. 380.
+  MUELLER, Max, antiquity of agriculture, ii. 243.
+  MULTIPLICITY of origin of pigeons, hypotheses of, discussed, i. 188-194.
+  MUNIZ, F., on Niata cattle, i. 90.
+  MUNRO, R., on the fertilisation of orchids, ii. 133;
+    reproduction of _Passiflora alata_, ii. 138.
+  "MURASSA" pigeon, i. 144.
+  MURPHY, J. J., the structure of the eye not producible by selection, ii.
+      222.
+  _Mus alexandrinus_, ii. 87-88.
+  _Musa sapientum_, _Chinensis_ and _Cavendishii_, i. 377.
+  _Muscari comosum_, ii. 185, 316.
+  MUSCLES, effects of use on, ii. 297.
+  MUSK duck, feral hybrid of, with the common duck, i. 190.
+  {466}
+  MUSMON, female, sometimes hornless, i. 95.
+  MUTILATIONS, inheritance or non-inheritance of, ii. 22-24, 397.
+  MYATT, on a five-leaved variety of the strawberry, i. 353.
+  MYOPIA, hereditary, ii. 8.
+  MYRIAPODA, regeneration of lost parts in, ii. 15, 294.
+
+  NAILS, growing on stumps of fingers, ii. 394.
+  NAIS, scission of, ii. 358.
+  NAMAQUAS, cattle of the, i. 88, ii. 207.
+  NARCISSUS, double, becoming single in poor soil, ii. 167.
+  NARVAEZ, on the cultivation of native plants in Florida, i. 312.
+  _Nasua_, sterility of, in captivity, ii. 152.
+  "NATAS," or Niatas, a South American breed of cattle, i. 89-91.
+  NATHUSIUS, H. von, on the pigs of the Swiss lake-dwellings, i. 68;
+    on the races of pigs, i. 65-68;
+    convergence of character in highly-bred pigs, i. 73, ii. 241;
+    causes of changes in the form of the pig's skull, i. 72-73;
+    changes in breeds of pigs by crossing, i. 78;
+    change of form in the pig, ii. 279;
+    effects of disuse of parts in the pig, ii. 299;
+    period of gestation in the pig, i. 74;
+    appendages to the jaw in pigs, i. 76;
+    on _Sus pliciceps_, i. 70;
+    period of gestation in sheep, i. 97;
+    on Niata cattle, i. 89;
+    on short-horn cattle, ii. 118;
+    on interbreeding, ii. 116;
+    in the sheep, ii. 120;
+    in pigs, ii. 122;
+    unconscious selection in cattle and pigs, ii. 214;
+    variability of highly selected races, ii. 238.
+  NATO, P., on the Bizzaria orange, i. 391.
+  NATURAL selection, its general principles, i. 2-14.
+  NATURE, sense in which the term is employed, i. 6.
+  NAUDIN, supposed rules of transmission in crossing plants, ii. 68;
+    on the nature of hybrids, ii. 48-49;
+    essences of the species in hybrids, ii. 386, 401;
+    reversion of hybrids, ii. 36, 49-50;
+    reversion in flowers by stripes and blotches, ii. 37;
+    hybrids of _Linaria vulgaris_ and _purpurea_, ii. 94;
+    pelorism in _Linaria_, ii. 58, 346;
+    crossing of peloric _Linaria_ with the normal form, ii. 70;
+    variability in _Datura_, ii. 266;
+    hybrids of _Datura laevis_ and _stramonium_, i. 392;
+    prepotency of transmission of _Datura stramonium_ when crossed, ii. 67;
+    on the pollen of _Mirabilis_ and of hybrids, i. 389;
+    fertilisation of _Mirabilis_, ii. 363;
+    crossing of _Chamaerops humilis_ and the date palm, i. 399;
+    cultivated Cucurbitaceae, i. 357-360, ii. 108;
+    rudimentary tendrils in gourds, ii. 316;
+    dwarf _Cucurbitae_, ii. 330;
+    relation between the size and number of the fruit in _Cucurbita pepo_,
+        ii. 343;
+    analogous variation in _Cucurbitae_, ii. 349;
+    acclimatisation of Cucurbitaceae, ii. 313;
+    production of fruit by sterile hybrid Cucurbitaceae, ii. 172;
+    on the melon, i. 360, ii. 108, 275;
+    incapacity of the cucumber to cross with other species, i. 359.
+  NECTARINE, i. 336-344;
+    derived from the peach, i. 337, 339-342;
+    hybrids of, i. 339;
+    persistency of characters in seedling, i. 340;
+    origin of, _ibid._;
+    produced on peach trees, i. 340-341;
+    producing peaches, i. 341;
+    variation in, i. 342-343;
+    bud-variation in, i. 374;
+    glands in the leaves of the, ii. 231;
+    analogous variation in, ii. 348.
+  NECTARY, variations of, in pansies, i. 369.
+  NEES, on changes in the odour of plants, ii. 274.
+  "NEGRO" cat, i. 46.
+  NEGROES, polydactylism in, ii. 14;
+    selection of cattle practised by, ii. 207.
+  NEOLITHIC period, domestication of _Bos longifrons_ and _primigenius_ in
+      the, i. 81;
+    cattle of the, distinct from the original species, i. 87;
+    domestic goat in the, i. 101;
+    cereals of the, i. 317.
+  NERVE, optic, atrophy of the, ii. 297.
+  NEUMEISTER, on the Dutch and German pouter pigeons, i. 138;
+    on the Jacobin pigeon, i. 154;
+    duplication of the middle flight feather in pigeons, i. 159;
+    on a peculiarly coloured breed of pigeons, "Staarhalsige Taube," i.
+        161;
+    fertility of hybrid pigeons, i. 192;
+    mongrels of the trumpeter pigeon, ii. 66;
+    period of perfect plumage in pigeons, ii. 77;
+    advantage of crossing pigeons, ii. 126.
+  NEURALGIA, hereditary, ii. 79.
+  NEW ZEALAND, feral cats of, i. 47;
+    cultivated plants of, i. 311.
+  NEWFOUNDLAND dog, modification of, in England, i. 42.
+  NEWMAN, E., sterility of Sphingidae under certain conditions, ii. 158.
+  NEWPORT, G., non-copulation of _Vanessae_ in confinement, ii. 157;
+    regeneration of limbs in myriapoda, ii. 294;
+    fertilisation of the ovule in batrachia, ii. 363.
+  NEWT, polydactylism in the, ii. 14.
+  NEWTON, A., absence of sexual distinctions in the Columbidae, i. 162;
+    production of a "black-shouldered" pea-hen among the ordinary kind, i.
+        291;
+    on hybrid ducks, ii. 157.
+  NGAMI, Lake, cattle of, i. 88.
+  "NIATA" cattle, i. 89-91;
+    resemblance of to _Sivatherium_, i. 89;
+  {467}
+    prepotency of transmission of character by, ii. 66.
+  "NICARD" rabbit, i. 107.
+  NICHOLSON, Dr., on the cats of Antigua, i. 46;
+    on the sheep of Antigua, i. 98.
+  _Nicotiana_, crossing of varieties and species of, ii. 108;
+    prepotency of transmission of characters in species of, ii. 67;
+    contabescence of female organs in, ii. 166.
+  _Nicotiana glutinosa_, ii. 108.
+  NIEBUHR, on the heredity of mental characteristics in some Roman
+      families, ii. 65.
+  NIGHT-BLINDNESS, non-reversion to, ii. 36.
+  NILSSON, Prof., on the barking of a young wolf, i. 27;
+    parentage of European breeds of cattle, i. 80, 81;
+    on _Bos frontosus_ in Scania, i. 81.
+  NIND, Mr., on the dingo, i. 39.
+  "NISUS formativus," i. 293, 294, 355.
+  NITZSCH, on the absence of the oil-gland in certain Columbae, i. 147.
+  NON-INHERITANCE, causes of, ii. 24-26.
+  "NONNAIN" pigeon, i. 154.
+  NORDMANN, dogs of Awhasie, i. 25.
+  NORMANDY, pigs of, with appendages under the jaw, i. 75.
+  NORWAY, striped ponies of, i. 58.
+  NOTT and Gliddon, on the origin of the dog, i. 16;
+    mastiff represented on an Assyrian tomb, i. 17;
+    on Egyptian dogs, i. 18;
+    on the Hare-Indian dog, i. 22.
+  _Notylia_, ii. 135.
+  NOURISHMENT, excess of, a cause of variability, ii. 257.
+  NUMBER, importance of, in selection, ii. 235.
+  _Numida ptilorhyncha_, the original of the Guinea-fowl, i. 294.
+  NUN pigeon, i. 155;
+    known to Aldrovandi, i. 207.
+  NUTMEG tree, ii. 237.
+
+  OAK, weeping, i. 361, ii. 18, 241;
+    pyramidal, i. 361;
+    Hessian, i. 361;
+    late-leaved, i. 363;
+    variation in persistency of leaves of, i. 363;
+    valueless as timber at the Cape of Good Hope, ii. 274;
+    changes in, dependent on age, i. 387;
+    galls of the, ii. 282.
+  OATS, wild, i. 313;
+    in the Swiss lake-dwellings, i. 319.
+  OBERLIN, change of soil beneficial to the potato, ii. 146.
+  ODART, Count, varieties of the vine, i. 333, ii. 278;
+    bud-variation in the vine, i. 375.
+  ODOUR and colour, correlation of, ii. 325.
+  _Oecidium_, ii. 284.
+  _Oenothera biennis_, bud-variation in, i. 382.
+  OGLE, W., resemblance of twins, ii. 252.
+  OIL-GLAND, absence of, in fantail pigeons, i. 147, 160.
+  OLDFIELD, Mr., estimation of European dogs among the natives of
+      Australia, ii. 215.
+  OLEANDER, stock affected by grafting in the, i. 394.
+  OLLIER, Dr., insertion of the periosteum of a dog beneath the skin of a
+      rabbit, ii. 369.
+  _Oncidium_, reproduction of, ii. 133-135, 164.
+  ONIONS, crossing of, ii. 90;
+    white, liable to the attacks of fungi and disease, ii. 228, 336.
+  _Ophrys apifera_, self-fertilisation of, ii. 91;
+    formation of pollen by a petal in, ii. 392.
+  _Opuntia leucotricha_, ii. 277.
+  ORANGE, i. 334-336;
+    crossing of, ii. 91;
+    with the lemon, i. 399, ii. 365;
+    naturalisation of, in Italy, ii. 308;
+    variation of, in North Italy, ii. 256;
+    peculiar variety of, ii. 331;
+    Bizzaria, i. 391;
+    trifacial, _ibid._
+  ORCHIDS, reproduction of, i. 402, 403; ii. 133-135.
+  ORFORD, Lord, crossing greyhounds with the bulldog, i. 41.
+  ORGANISMS, origin of, i. 13.
+  ORGANISATION, advancement in, i. 8.
+  ORGANS, rudimentary and aborted, ii. 315-318;
+    multiplication of abnormal, ii. 391.
+  ORIOLE, assumption of hen-plumage by a male in confinement, ii. 158.
+  ORKNEY islands, pigs of, i. 70;
+    pigeons of, i. 184.
+  ORTHOPTERA, regeneration of hind legs in the, ii. 294.
+  _Orthosia munda_, ii. 157.
+  ORTON, R., on the effects of cross-breeding on the female, i. 404;
+    on the Manx cat, ii. 66;
+    on mongrels from the silk-fowl, ii. 67.
+  OSBORNE, Dr., inherited mottling of the iris, ii. 10.
+  OSPREY, preying on Black-fowls, ii. 230.
+  OSTEN-SACKEN, Baron, on American oak galls, ii. 282.
+  OSTEOLOGICAL characters of pigs, i. 66, 67, 71-74;
+    of rabbits, i. 115-130;
+    of pigeons, i. 162-167;
+    of ducks, i. 282-284.
+  OSTRICH, diminished fertility of the, in captivity, ii. 156.
+  OSTYAKS, selection of dogs by the, ii. 206.
+  OTTER, ii. 151.
+  "OTTER" sheep of Massachusetts, i. 100.
+  OUDE, feral humped cattle in, i. 79.
+  OUISTITI, breed in Europe, ii. 153.
+  {468}
+  OVARY, variation of, in _Cucurbita moschata_, i. 359;
+    development of, independently of pollen, i. 403.
+  _Ovis montana_, i. 99.
+  OVULES and buds, identity of nature of, ii. 360.
+  OWEN, Capt., on stiff-haired cats at Mombas, i. 46.
+  OWEN, Prof. R., palaeontological evidence as to the origin of dogs, i.
+      15;
+    on _Bos longifrons_, i. 81;
+    on the skull of the "Niata" cattle, i. 89, 90;
+    on fossil remains of rabbits, i. 104;
+    on the significance of the brain, i. 124;
+    on the number of digits in the Ichthyopterygia, ii. 16;
+    on metagenesis, ii. 366;
+    theory of reproduction and parthenogenesis, ii. 375.
+  OWL, eagle, breeding in captivity, ii. 154.
+  OWL pigeon, i. 148;
+    African, figured, i. 149;
+    known in 1735, i. 209.
+  _Oxalis_, trimorphic species of, ii. 400.
+  _Oxalis rosea_, ii. 132.
+  OXLEY, Mr., on the nutmeg tree, ii. 237.
+  OYSTERS, differences in the shells of, ii. 280.
+
+  PACA, sterility of the, in confinement, ii. 152.
+  PACIFIC islands, pigs of the, i. 70.
+  PADUA, earliest known flower garden at, ii. 217.
+  PADUAN fowl of Aldrovandi, i. 247.
+  _Paeonia moutan_, ii. 205.
+  PAEONY, tree, ancient cultivation of, in China, ii. 205.
+  PAMPAS, feral cattle on the, i. 85.
+  _Pandanus_, ii. 256.
+  PANGENESIS, hypothesis of, ii. 357-404.
+  _Panicum_, seeds of, used as food, i. 309;
+    found in the Swiss lake-dwellings, i. 317.
+  PANSY, i. 368-370.
+  PAPPUS, abortion of the, in _Carthamus_, ii. 316.
+  PAGET, on the Hungarian sheep dog, i. 24.
+  PAGET, inheritance of cancer, ii. 7;
+    hereditary elongation of hairs in the eyebrow, ii. 8;
+    period of inheritance of cancer, ii. 79-80;
+    on _Hydra_, ii. 293;
+    on the healing of wounds, ii. 294;
+    on the reparation of bones, _ibid._;
+    growth of hair near inflamed surfaces or fractures, ii. 295;
+    on false membranes, _ibid._;
+    compensatory development of the kidney, ii. 300;
+    bronzed skin in disease of supra-renal capsules, ii. 331;
+    unity of growth and gemmation, ii. 359;
+    independence of the elements of the body, ii. 369;
+    affinity of the tissues for special organic substances, ii. 380.
+  PALLAS, on the influence of domestication upon the sterility of
+      intercrossed species, i. 31, 83, 193, ii. 109;
+    hypothesis that variability is wholly due to crossing, i. 188, 374, ii.
+        250, 264;
+    on the origin of the dog, i. 16;
+    variation in dogs, i. 33;
+    crossing of dog and jackal, i. 25;
+    origin of domestic cats, i. 43;
+    origin of Angora cat, i. 45;
+    on wild horses, i. 52, 60;
+    on Persian sheep, i. 94;
+    on Siberian fat-tailed sheep, ii. 279;
+    on Chinese sheep, ii. 315;
+    on Crimean varieties of the vine, i. 333;
+    on a grape with rudimentary seeds, ii. 316;
+    on feral musk-ducks, ii. 46;
+    sterility of Alpine plants in gardens, ii. 163;
+    selection of white-tailed yaks, ii. 206.
+  _Paradoxurus_, sterility of species of, in captivity, ii. 151.
+  PARAGUAY, cats of, i. 46;
+    cattle of, i. 89;
+    horses of, ii. 102;
+    dogs of, ii. 102;
+    black-skinned domestic fowl of, i. 232.
+  PARALLEL variation, ii. 348-352.
+  PARAMOS, woolly pigs of, i. 78.
+  PARASITES, liability to attacks of, dependent on colour, ii. 228.
+  PARIAH dog, with crooked legs, i. 17;
+    resembling the Indian wolf, i. 24.
+  PARISET, inheritance of handwriting, ii. 6.
+  PARKER, W. K., number of vertebrae in fowls, i. 266.
+  PARKINSON, Mr., varieties of the hyacinth, i. 370.
+  PARKYNS, Mansfield, on _Columba guinea_, i. 183.
+  PARMENTIER, differences in the nidification of pigeons, i. 178;
+    on white pigeons, ii. 230.
+  PARROTS, general sterility of, in confinement, ii. 155;
+    alteration of plumage of, ii. 280.
+  PARSNIP, reversion in, ii. 31;
+    influence of selection on, ii. 201;
+    experiments on, ii. 277;
+    wild, enlargement of roots of, by cultivation, i. 326.
+  PARTHENOGENESIS, ii. 359, 364.
+  PARTRIDGE, sterility of, in captivity, ii. 156.
+  PARTURITION, difficult, hereditary, ii. 8.
+  _Parus major_, ii. 231.
+  _Passiflora_, self-impotence in species of, ii. 137-138;
+    contabescence of female organs in, ii. 166.
+  _Passiflora alata_, fertility of, when grafted, ii. 188.
+  PASTURE and climate, adaptation of breeds of sheep to, i. 96, 97.
+  PASTRANA, Julia, peculiarities in the hair and teeth of, ii. 328.
+  PATAGONIA, crania of pigs from, i. 77.
+  PATAGONIAN rabbit, i. 105.
+  {469}
+  PATERSON, R., on the Arrindy silk moth, ii. 306.
+  PAUL, W., on the hyacinth, i. 370;
+    varieties of pelargoniums, i. 378;
+    improvement of pelargoniums, ii. 216.
+  _Pavo cristatus_ and _muticus_, hybrids of, i. 290.
+  _Pavo nigripennis_, i. 290-291.
+  "PAVODOTTEN-TAUBE," i. 141.
+  PEACH, i. 336-344;
+    derived from the almond, i. 337;
+    stones of, figured, _ibid._;
+    contrasted with almonds, i. 338;
+    double-flowering, i. 338-339, 343;
+    hybrids of, i. 339;
+    persistency of races of, _ibid._;
+    trees producing nectarines, i. 340-341;
+    variation in, i. 342-343, ii. 256;
+    bud-variation in, i. 374;
+    pendulous, ii. 18;
+    variation by selection in, ii. 218;
+    peculiar disease of the, ii. 228;
+    glands on the leaves of the, ii. 231;
+    antiquity of the, ii. 308;
+    increased hardiness of the, _ibid._;
+    varieties of, adapted for forcing, ii. 310;
+    yellow-fleshed, liable to certain diseases, ii. 336.
+  PEACH-ALMOND, i. 338.
+  PEAFOWL, origin of, i. 290;
+    japanned or black-shouldered, i. 290-291;
+    feral, in Jamaica, i. 190;
+    comparative fertility of, in wild and tame states, ii. 112, 268;
+    white, ii. 332.
+  PEARS, i. 350;
+    bud-variation in, i. 376;
+    reversion in seedling, ii. 31;
+    inferiority of, in Pliny's time, ii. 215;
+    winter nelis, attacked by aphides, ii. 231;
+    soft-barked varieties of, attacked by wood-boring beetles, ii. 231;
+    origination of good varieties of, in woods, ii. 260;
+    Forelle, resistance of, to frost, ii. 306.
+  PEAS, i. 326-330;
+    origin of, 326;
+    varieties of, 326-329;
+    found in Swiss lake-dwellings, i. 317, 319, 326-329;
+    fruit and seeds figured, i. 328;
+    persistency of varieties, i. 329;
+    intercrossing of varieties, i. 330, 397, ii. 129;
+    effect of crossing on the female organs in, i. 398;
+    double-flowered, ii. 168;
+    maturity of, accelerated by selection, ii. 201;
+    varieties of, produced by selection, ii. 218;
+    thin-shelled, liable to the attacks of birds, ii. 231;
+    reversion of, by the terminal seed in the pod, ii. 347.
+  PECCARY, breeding of the, in captivity, ii. 150.
+  PEDIGREES of horses, cattle, greyhounds, game-cocks, and pigs, ii. 3.
+  PEGU, cats of, i. 47;
+    horses of, i. 53.
+  PELARGONIUMS, multiple origin of, i. 364;
+    zones of, i. 366;
+    bud-variation in, i. 378;
+    variegation in, accompanied by dwarfing, i. 384;
+    pelorism in, ii. 167, 345;
+    by reversion, ii. 59;
+    advantage of change of soil to, ii. 147;
+    improvement of, by selection, ii. 216;
+    scorching of, ii. 229;
+    numbers of, raised from seed, ii. 235;
+    effects of conditions of life on, ii. 274;
+    stove-variety of, ii. 311;
+    correlation of contracted leaves and flowers in, ii. 330-331.
+  _Pelargonium fulgidum_, conditions of fertility in, ii. 164.
+  "PELONES," a Columbian breed of cattle, i. 88.
+  PELORIC flowers, tendency of, to acquire the normal form, ii. 70;
+    fertility or sterility of, ii. 166-167.
+  PELORIC races of _Gloxinia speciosa_ and _Antirrhinum majus_, i. 365.
+  PELORISM, ii. 58-60, 345-346.
+  PELVIS, characters of, in rabbits, i. 122-123;
+    in pigeons, i. 166;
+    in fowls, i. 268;
+    in ducks, i. 284.
+  PEMBROKE cattle, i. 81.
+  PENDULOUS trees, i. 361, ii. 348;
+    uncertainty of transmission of, ii. 18-19.
+  PENGUIN ducks, i. 280, 282;
+    hybrid of the, with the Egyptian goose, i. 282.
+  PENNANT, production of wolf-like curs at Fochabers, i. 37;
+    on the Duke of Queensberry's wild cattle, i. 84.
+  _Pennisetum_, seeds of, used as food in the Punjab, i. 309.
+  _Pennisetum distichum_, seeds of, used as food in Central Africa, i. 308.
+  PERCIVAL, Mr., on inheritance in horses, ii. 10;
+    on horn-like processes in horses, i. 50.
+  _Perdix rubra_, occasional fertility of, in captivity, ii. 156.
+  PERIOD of action of causes of variability, ii. 269.
+  PERIOSTEUM of a dog, producing bone in a rabbit, ii. 369.
+  PERIWINKLE, sterility of, in England, ii. 170.
+  PERSIA, estimation of pigeons in, i. 205;
+    carrier pigeon of, i. 141;
+    tumbler pigeon of, i. 150;
+    cats of, i. 45-47;
+    sheep of, i. 94.
+  _Persica intermedia_, i. 338.
+  PERSISTENCE of colour in horses, i. 50;
+    of generic peculiarities, i. 111.
+  PERU, antiquity of maize in, i. 320;
+    peculiar potato from, i. 331;
+    selection of wild animals practised by the Incas of, ii. 207-208.
+  "PERUECKEN-TAUBE," i. 154.
+  PETALS, rudimentary, in cultivated plants, ii. 316;
+    producing pollen, ii. 392.
+  PETUNIAS, multiple origin of, i. 364;
+    double-flowered, ii. 167.
+  "PFAUEN-TAUBE," i. 146.
+  _Phacochoerus Africanus_, i. 76.
+  _Phalaenopsis_, pelorism in, ii. 346.
+  PHALANGES, deficiency of, ii. 73.
+  {470}
+  _Phaps chalcoptera_, ii. 349.
+  _Phaseolus multiflorus_, ii. 309, 322.
+  _Phaseolus vulgaris_, ii. 309.
+  _Phasianus pictus_, i. 275.
+  _Phasianus Amherstiae_, i. 275.
+  PHEASANT, assumption of male plumage by the hen, ii. 51;
+    wildness of hybrids of, with the common fowl, ii. 45;
+    prepotency of the, over the fowl, ii. 68;
+    diminished fecundity of the, in captivity, ii. 155.
+  PHEASANTS, golden and Lady Amherst's, i. 275.
+  PHEASANT-FOWLS, i. 244.
+  PHILIPEAUX, regeneration of limbs in the salamander, ii. 376.
+  PHILIPPAR, on the varieties of wheat, i. 314.
+  PHILIPPINE Islands, named breeds of game fowl in the, i. 232.
+  PHILLIPS, Mr., on bud-variation in the potato, i. 385.
+  _Phlox_, bud-variation by suckers in, i. 384.
+  PHTHISIS, affection of the fingers in, ii. 332.
+  PICKERING, Mr., on the grunting voice of humped cattle, i. 79;
+    occurrence of the head of a fowl in an ancient Egyptian procession, i.
+        246;
+    seeding of ordinarily seedless fruits, ii. 168;
+    extinction of ancient Egyptian breeds of sheep and oxen, ii. 425;
+    on an ancient Peruvian gourd, ii. 429.
+  PICOTEES, effect of conditions of life on, ii. 273.
+  PICTET, A., oriental names of the pigeon, i. 205.
+  PICTET, Prof., origin of the dog, i. 15;
+    on fossil oxen, i. 81.
+  PIEBALDS, probably due to reversion, ii. 37.
+  PIGEAUX, hybrids of the hare and rabbit, ii. 99, 152.
+  PIGEON a cravate, i. 148.
+  PIGEON Bagadais, i. 142, 143.
+  PIGEON coquille, i. 155.
+  PIGEON cygne, i. 143.
+  PIGEON heurte, i. 156.
+  PIGEON Patu plongeur, i. 156.
+  PIGEON Polonais, i. 144.
+  PIGEON Romain, i. 142, 144.
+  PIGEON tambour, i. 154.
+  PIGEON Turc, i. 139.
+  PIGEONS, origin of, i. 131-134, 180-204;
+    classified table of breeds of, i. 136;
+    pouter, i. 137-139;
+    carrier, i. 139-142;
+    runt, i. 142-144;
+    barbs, i. 144-146;
+    fantail, i. 146-148;
+    turbit and owl, i. 148-149;
+    tumbler, i. 150-153;
+    Indian frill-back, i. 153;
+    Jacobin, i. 154;
+    trumpeter, i. 154;
+    other breeds of, i. 155-157;
+    differences of, equal to generic, i. 157-158;
+    individual variations of, i. 158-160;
+    variability of peculiarities characteristic of breeds in, i. 161;
+    sexual variability in, i. 161-162;
+    osteology of, i. 162-167;
+    correlation of growth in, i. 167-171, ii. 321;
+    young of some varieties naked when hatched, i. 170, ii. 332;
+    effects of disuse in, i. 172-177;
+    settling and roosting in trees, i. 181;
+    floating in the Nile to drink, i. 181;
+    Dovecot, i. 185-186;
+    arguments for unity of origin of, i. 188-204;
+    feral in various places, i. 190, ii. 33;
+    unity of coloration in, i. 195-197;
+    reversion of mongrel, to coloration of, _C. livia_, i. 197-202;
+    history of the cultivation of, i. 205-207;
+    history of the principal races of, i. 207-212;
+    mode of production of races of, i. 212-224;
+    reversion in, ii. 29, 47;
+    by age, ii. 38;
+    produced by crossing in, ii. 40, 48;
+    prepotency of transmission of character in breeds of, ii. 66-67;
+    sexual differences in some varieties of, ii. 74;
+    period of perfect plumage in, ii. 77;
+    effect of segregation on, ii. 86;
+    preferent pairing of, within the same breed, ii. 103;
+    fertility of, increased by domestication, ii. 112, 155;
+    effects of interbreeding and necessity of crossing, ii. 125-126;
+    indifference of, to change of climate, ii. 161;
+    selection of, ii. 195, 199, 204;
+    among the Romans, ii. 202;
+    unconscious selection of, ii. 211, 214;
+    facility of selection of, ii. 234;
+    white, liable to the attacks of hawks, ii. 230;
+    effects of disuse of parts in, ii. 298;
+    fed upon meat, ii. 304;
+    effect of first male upon the subsequent progeny of the female, i. 405;
+    homology of the leg and wing feathers in, ii. 323;
+    union of two outer toes in feather-legged, _ibid._;
+    correlation of beak, limbs, tongue, and nostrils in, ii. 324;
+    analogous variation in, ii. 349-350;
+    permanence of breeds of, ii. 429.
+  PIGS, of Swiss lake-dwellings, i. 67-68;
+    types of, derived from _Sus scrofa_ and _Sus indica_, i. 66-67;
+    Japanese (_Sus pliciceps_, Gray), figured, i. 69;
+    of Pacific islands, i. 70, ii. 87;
+    modifications, of skull in, i. 71-73;
+    length of intestines in, i. 73, ii. 303;
+    period of gestation of, i. 74;
+    number of vertebrae and ribs in, i. 74;
+    anomalous forms, i. 75-76;
+    development of tusks and bristles in, i. 76;
+    striped young of, i. 76-77;
+    reversion of feral, to wild type, i. 77-78, ii. 33, 47;
+    production and changes of breeds of, by intercrossing, i. 78;
+    effects produced by the first male upon the subsequent progeny of the
+        female, i. 404;
+    two-legged race of, ii. 4;
+  {471}
+    polydactylism in, ii. 14;
+    cross-reversion in, ii. 35;
+    hybrid, wildness of, ii. 45;
+    monstrous development of a proboscis in, ii. 57;
+    disappearance of tusks in male under domestication, ii, 74;
+    solid hoofed, ii. 429;
+    crosses of, ii. 93, 95;
+    mutual fertility of all varieties of, ii. 110;
+    increased fertility by domestication, ii. 111;
+    ill effects of close interbreeding in, ii. 121-122;
+    influence of selection on, ii. 198;
+    prejudice against certain colours in, ii. 210, 229, 336;
+    unconscious selection of, ii. 214;
+    black Virginian, ii. 227, 336;
+    similarity of the best breeds of, ii. 241;
+    change of form in, ii. 279;
+    effects of disuse of parts in, ii. 299;
+    ears of, ii. 301;
+    correlations in, ii. 327;
+    white, buck-wheat injurious to, ii. 337;
+    tail of, grafted upon the back, ii. 369;
+    extinction of the older races of, ii. 426.
+  PIMENTA, ii. 91.
+  PIMPERNEL, ii. 190.
+  PINE-APPLE, sterility and variability of the, ii. 262.
+  PINK, Chinese. 322.
+  PINKS, bud-variation in, i. 381;
+    improvement of, ii. 216.
+  _Pinus pumilio_, _Mughus_, and _nana_, varieties of _P. sylvestris_, i.
+      363.
+  _Pinus sylvestris_, i. 363, ii. 310;
+    hybrids of, with _P. nigricans_, ii. 130.
+  PIORRY, on hereditary disease, ii. 7, 78.
+  _Pistacia lentiscus_, ii. 274.
+  PISTILS, rudimentary, in cultivated plants, ii. 316.
+  PISTOR, sterility of some mongrel pigeons, i. 192;
+    fertility of pigeons, ii. 112.
+  _Pisum arvense_ and _sativum_, i. 326.
+  PITYRIASIS versicolor, inheritance of, ii. 79.
+  PLANCHON, G., on a fossil vine, i. 332;
+    sterility of _Jussiaea grandifiora_ in France, ii. 170.
+  PLANE tree, variety of the, i. 362.
+  PLANTIGRADE carnivora, general sterility of the, in captivity, ii. 151.
+  PLANTS, progress of cultivation of, i. 305-312;
+    cultivated, their geographical derivation, i. 311;
+    crossing of, ii. 98, 99, 127;
+    comparative fertility of wild and cultivated, ii. 112-113;
+    self-impotent, ii. 131-140;
+    dimorphic and trimorphic, ii. 132, 140;
+    sterility of, from changed conditions, ii. 163-165;
+    from contabescence of anthers, ii. 165-166;
+    from monstrosities, ii. 166-167;
+    from doubling of the flowers, ii. 167-168;
+    from seedless fruit, ii. 168;
+    from excessive development of vegetative organs, ii. 168-171;
+    influence of selection on, ii. 199-201;
+    variation by selection, in useful parts of, ii. 217-219;
+    variability of, ii. 237;
+    variability of, induced by crossing, ii. 265;
+    direct action of change of climate on, ii. 277;
+    change of period of vegetation in, ii. 304-305;
+    varieties of, suitable to different climates, ii. 306;
+    correlated variability of, ii. 330-331;
+    antiquity of races of, ii. 429.
+  PLASTICITY, inheritance of, ii. 241.
+  PLATEAU, F., on the vision of amphibious animals, ii. 223.
+  _Platessa flesus_, ii. 53.
+  PLATO, notice of selection in breeding dogs by, ii. 212.
+  PLICA polonica, ii. 276.
+  PLINY, on the crossing of shepherd's dogs with the wolf, i. 24;
+    on Pyrrhus' breed of cattle, ii. 202;
+    on the estimation of pigeons among the Romans, i. 205;
+    pears described by, ii. 215.
+  PLUM, i. 345-347;
+    stones figured, i. 345;
+    varieties of the, i. 345-346, ii. 219;
+    bud-variation in the, i. 375;
+    peculiar disease of the, ii. 227;
+    flower-buds of, destroyed by bullfinches, ii. 232;
+    purple-fruited, liable to certain diseases, ii. 336.
+  PLUMAGE, inherited peculiarities of, in pigeons, i. 160-161;
+    sexual peculiarities of, in fowls, i. 251-255.
+  PLURALITY of races, Pouchet's views on, i. 2.
+  _Poa_, seeds of, used as food, i. 308;
+    species of, propagated by bulblets, ii. 170.
+  PODOLIAN cattle, i. 80.
+  POINTERS, modification of, i. 42;
+    crossed with the foxhound, ii. 95.
+  POIS sans parchemin, ii. 231.
+  POITEAU, origin of _Cytisus Adami_, i. 390;
+    origin of cultivated varieties of fruit-trees, ii. 260.
+  POLISH fowl, i. 227, 250, 254, 256-257, 262;
+    skull figured, i. 262;
+    section of skull figured, i. 263;
+    development of protuberance of skull, i. 250;
+    furcula figured, i. 268.
+  POLISH, or Himalayan rabbit, i. 108.
+  POLLEN, ii. 363-364;
+    action of, ii. 108;
+    injurious action of, in some orchids, ii. 134-135;
+    resistance of, to injurious treatment, ii. 164;
+    prepotency of, ii. 187.
+  POLLOCK, Sir F., transmission of variegated leaves in _Ballota nigra_, i.
+      383;
+    on local tendency to variegation, ii. 274.
+  POLYANTHUS, ii. 21.
+  POLYDACTYLISM, inheritance of, ii. 12-16;
+    significance of, ii. 16-17.
+  _Polyplectron_, i. 255.
+  PONIES, most frequent on islands and mountains, i. 52;
+    Javanese, i. 53.
+  POOLE, Col., on striped Indian horses, i. 58, 59;
+  {472}
+    on the young of _Asinus indicus_, ii. 43.
+  POPLAR, Lombardy, i. 361.
+  POEPPIG, on Cuban wild dogs, i. 27.
+  POPPY, found in the Swiss lake-dwellings, i. 317, 319;
+    with the stamens converted into pistils, i. 365;
+    differences of the, in different parts of India, ii. 165;
+    monstrous, fertility of, ii. 166;
+    black-seeded, antiquity of, ii. 429.
+  PORCUPINE, breeding of, in captivity, ii. 152.
+  PORCUPINE family, ii. 4, 76.
+  _Porphyrio_, breeding of a species of, in captivity, ii. 156.
+  PORTAL, on a peculiar hereditary affection of the eye, ii. 9.
+  PORTO Santo, feral rabbits of, i. 112.
+  _Potamochoerus penicillatus_, ii. 150.
+  POTATO, i. 330-331;
+    bud-variation by tubers in the, i. 384-385;
+    graft-hybrid of, by union of half-tubers, i. 395;
+    individual self-impotence in the, ii. 137;
+    sterility of, ii. 169;
+    advantage of change of soil to the, ii. 146;
+    relation of tubers and flowers in the, ii. 343.
+  POTATO, sweet, sterility of the, in China, ii. 169;
+    varieties of the, suited to different climates, ii. 309.
+  POUCHET, M., his views on plurality of races, i. 2.
+  POUTER pigeons, i. 137-139;
+    furcula figured, i. 167;
+    history of, i. 207.
+  POWIS, Lord, experiments in crossing humped and English cattle, i. 83,
+      ii. 45.
+  POYNTER, Mr., on a graft-hybrid rose, i. 396.
+  PRAIRIE wolf, i. 22.
+  PRECOCITY of highly-improved breeds, ii. 321.
+  PREPOTENCY of pollen, ii. 187.
+  PREPOTENCY of transmission of character, ii. 65, 174;
+    in the Austrian emperors and some Roman families, ii. 65;
+    in cattle, ii. 65-66;
+    in sheep, ii. 66;
+    in cats, _ibid._;
+    in pigeons, ii. 66-67;
+    in fowls, ii. 67;
+    in plants, _ibid._;
+    in a variety of the pumpkin, i. 358;
+    in the jackal over the dog, ii. 67;
+    in the ass over the horse, _ibid._;
+    in the pheasant over the fowl, ii. 68;
+    in the penguin duck over the Egyptian goose, _ibid._;
+    discussion of the phenomena of, ii. 69-71.
+  PRESCOTT, Mr., on the earliest known European flower-garden, ii. 217.
+  PRESSURE, mechanical, a cause of modification, ii. 344-345.
+  PREVOST and Dumas, on the employment of several spermatozoids to
+      fertilise one ovule, ii. 363.
+  PRICE, Mr., variations in the structure of the feet in horses, i. 50.
+  PRICHARD, Dr., on polydactylism in the negro, ii. 14;
+    on the Lambert family, ii. 77;
+    on an albino negro, ii. 229;
+    on Plica polonica, ii. 276.
+  PRIMROSE, ii. 21;
+    double, rendered single by transplantation, ii. 167.
+  _Primula_, intercrossing of species of, i. 336;
+    contabescence in, ii. 166;
+    hose and hose, i. 365;
+    with coloured calyces, sterility of, ii. 166.
+  _Primula sinensis_, reciprocally dimorphic, ii. 132.
+  _Primula veris_, ii. 21, 109, 182.
+  _Primula vulgaris_, ii. 21, 109.
+  PRINCE, Mr., on the intercrossing of strawberries, i. 352.
+  _Procyon_, sterility of, in captivity, ii. 152.
+  PROLIFICACY, increased by domestication, ii. 174.
+  PROPAGATION, rapidity of, favourable to selection, ii. 297.
+  PROTOZOA, reproduction of the, ii. 376.
+  _Prunus armeniaca_, i. 344-345.
+  _Prunus avium_, i. 347.
+  _Prunus cerasus_, i. 347, 375.
+  _Prunus domestica_, i. 345.
+  _Prunus insititia_, i. 345-347.
+  _Prunus spinosa_, i. 345.
+  PRUSSIA, wild horses in, i. 60.
+  _Psittacus erithacus_, ii. 155.
+  _Psittacus macoa_, ii. 155.
+  _Psophia_, general sterility of, in captivity, ii. 157.
+  PTARMIGAN fowls, i. 228.
+  _Pulex penetrans_, ii. 275.
+  PUMPKINS, i. 357.
+  PUNO ponies of the Cordillera, i. 52.
+  PURSER, Mr. on _Cytisus Adami_, i. 389.
+  PUSEY, Mr., preference of hares and rabbits for common rye, ii. 232.
+  PUTSCHE and Vertuch, varieties of the potato, i. 330.
+  PUVIS, effects of foreign pollen on apples, i. 401;
+    supposed non-variability of monotypic genera, ii. 266.
+  _Pyrrhula vulgaris_, ii. 232;
+    assumption of the hen-plumage by the male, in confinement, ii. 158.
+  PYRRHUS, his breed of cattle, ii. 202.
+  _Pyrus_, fastigate Chinese species of, ii. 277.
+  _Pyrus acerba_, i. 348.
+  _Pyrus aucuparia_, ii. 230.
+  _Pyrus communis_, i. 350, 376.
+  _Pyrus malus_, i. 348, 376.
+  _Pyrus paradisiaca_, i. 348.
+  _Pyrus praecox_, i. 348.
+
+  QUAGGA, effect of fecundation by, on the subsequent progeny of a mare, i.
+      403-404.
+  QUATREFAGES, A. de, on the burrowing of a bitch to litter, i. 77;
+  {473}
+    selection in the silkworm, i. 301;
+    development of the wings in the silkmoth, i. 303, ii. 298;
+    on varieties of the mulberry, i. 334;
+    special raising of eggs of the silkmoth, ii. 197;
+    on disease of the silkworm, ii. 228;
+    on monstrosities in insects, ii. 269, 391;
+    on the Anglo-Saxon race in America, ii. 276;
+    on a change in the breeding season of the Egyptian goose, ii. 304;
+    fertilisation of the _Teredo_, ii. 363;
+    tendency to similarity in the best races, ii. 241;
+    on his "_tourbillon vital_," ii. 61;
+    on the independent existence of the sexual elements, ii. 360.
+  _Quercus cerris_, i. 363.
+  _Quercus robur_ and _pedunculata_, hybrids of, ii. 130.
+  QUINCE, pears grafted on the, ii. 259.
+
+  RABBITS, domestic, their origin, i. 103-105;
+    of Mount Sinai and Algeria, i. 105;
+    breeds of, i. 105-111;
+    Himalayan, Chinese, Polish, or Russian, i. 108-111, ii. 97;
+    feral, i. 111-115;
+    of Jamaica, i. 112;
+    of the Falkland islands, i. 112;
+    of Porto Santo, i. 112-115, ii. 103, 279;
+    osteological characters of, i. 115-129;
+    discussion of modifications in, i. 129-130;
+    one-eared, transmission of peculiarity of, ii. 12;
+    reversion in feral, ii. 33;
+    in the Himalayan, ii. 41;
+    crossing of white and coloured Angora, ii. 92;
+    comparative fertility of wild and tame, ii. 111;
+    high-bred, often bad breeders, ii. 121;
+    selection of, ii. 204;
+    white, liable to destruction, ii. 230;
+    effects of disuse of parts in, ii. 298;
+    skull of, affected by drooping ears, ii. 301;
+    length of intestines in, ii. 303;
+    correlation of ears and skull in, ii. 324-325;
+    variations in skull of, ii. 350;
+    periosteum of a dog producing bone in, ii. 369.
+  RACE-HORSE, origin of, i. 54.
+  RACES, modification and formation of, by crossing, ii. 95-99;
+    natural and artificial, ii. 245;
+    Pouchet's views on plurality of, i. 2;
+    of pigeons, i. 207-212.
+  RADISHES, i. 326; crossing of, ii. 90;
+    varieties of, ii. 217-218.
+  RADCLYFFE, W. F., effect of climate and soil on strawberries, i. 354;
+    constitutional differences in roses, i. 367.
+  RADLKOFER, retrogressive metamorphosis in mosses and algae, ii. 361.
+  RAFFLES, Sir Stamford, on the crossing of Javanese cattle with _Bos
+      sondaicus_, ii. 206.
+  RAM, goat-like, from the Cape of Good Hope, ii. 66.
+  RANCHIN, heredity of diseases, ii. 7.
+  RANGE of gallinaceous birds on the Himalaya, i. 237.
+  _Ranunculus ficaria_, ii. 170.
+  _Ranunculus repens_, ii. 168.
+  RAPE, i. 325.
+  _Raphanus sativus_, ii. 343.
+  RASPBERRY, yellow-fruited, ii. 230.
+  RATTLESNAKE, experiments with poison of the, ii. 289.
+  RAVEN, stomach of, affected by vegetable diet, ii. 302.
+  RAWSON, A., self-impotence in hybrids of _Gladiolus_, ii. 139-140.
+  RE, Le Compte, on the assumption of a yellow colour by all varieties of
+      maize, i. 321.
+  REAUMUR, effect of confinement upon the cock, ii. 52;
+    fertility of fowls in most climates, ii. 161.
+  REED, Mr., atrophy of the limbs of rabbits, consequent on the destruction
+      of their nerves, ii. 297.
+  REGENERATION of amputated parts in man, ii. 14;
+    in the human embryo, ii. 15;
+    in the lower vertebrata, insects, and myriapoda, _ibid._
+  REINDEER, individuals recognised by the Laplanders, ii. 251.
+  REGNIER, early cultivation of the cabbage by the Celts, i. 324.
+  REISSEK, experiments in crossing _Cytisus purpureus_ and _laburnum_, i.
+      389;
+    modification of a _Thesium_ by _Oecidium_, ii. 284.
+  RELATIONS, characters of, reproduced in children, ii. 34.
+  RENGGER, occurrence of jaguars with crooked legs in Paraguay, i. 17;
+    naked dogs of Paraguay, i. 23, 31, ii. 93, 102;
+    feral dogs of La Plata, i. 27;
+    on the aguara, i. 26;
+    cats of Paraguay, i. 46, ii. 86, 151;
+    dogs of Paraguay, ii. 87;
+    feral pigs of Buenos Ayres, i. 77;
+    on the refusal of wild animals to breed in captivity, ii. 149;
+    on _Dicotyles labiatus_, ii. 150;
+    sterility of plantigrade carnivora in captivity, ii. 152;
+    on _Cavia aperea_, ii. 152;
+    sterility of _Cebus azarae_ in captivity, ii. 153;
+    abortions produced by wild animals in captivity, ii. 158.
+  REPRODUCTION, sexual and asexual, contrasted, ii. 361;
+    unity of forms of, ii. 383;
+    antagonism of, to growth, ii. 384.
+  _Reseda odorata_, ii. 237.
+  RETINITIS, pigmentary, in deaf-mutes, ii. 328.
+  REVERSION, ii. 28-29, 372-373, 396, 398-402;
+    in pigeons, ii. 29;
+    in cattle, ii. 29-30;
+    in sheep, ii. 30;
+    in fowls, ii. 31;
+    in the heartsease, _ibid._;
+    in vegetables, _ibid._;
+    in feral animals and plants, ii. 32-34;
+    to characters derived from a previous cross in man, dogs, pigeons,
+        pigs, and fowls, ii. 34-35;
+  {474}
+    in hybrids, ii. 36;
+    by bud-propagation in plants, ii. 36-38;
+    by age in fowls, cattle, &c., ii. 38-39;
+    caused by crossing, ii. 39-51;
+    explained by latent characters, ii. 51-56;
+    producing monstrosities, ii. 57;
+    producing peloric flowers, ii. 58-60;
+    of feral pigs to the wild type, i. 77-78;
+    of supposed feral rabbits to the wild type, i. 104, 111, 115;
+    of pigeons, in coloration, when crossed, i. 197-202;
+    in fowls, i. 239-246;
+    in the silkworm, i. 302;
+    in the pansy, i. 369;
+    in a pelargonium, i. 378;
+    in Chrysanthemums, i. 379;
+    of varieties of the China rose in St. Domingo, i. 380;
+    by buds in pinks and carnations, i. 381;
+    of laciniated varieties of trees to the normal form, i. 382;
+    in variegated leaves of plants, i. 383-384;
+    in tulips, i. 386;
+    of suckers of the seedless barberry to the common form, i. 384;
+    by buds in hybrids of _Tropaeolum_, i. 392;
+    in plants, i. 409;
+    of crossed peloric snapdragons, ii. 71;
+    analogous variations due to, ii. 349-351.
+  REYNIER, selection practised by the Celts, ii. 202-203.
+  RHINOCEROS, breeding in captivity in India, ii. 150.
+  _Rhododendron_, hybrid, ii. 265.
+  _Rhododendron ciliatum_, ii. 277.
+  _Rhododendron Dalhousiae_, effect of pollen of _R. Nuttallii_ upon, i.
+      400.
+  RHUBARB, not medicinal when grown in England, ii. 274.
+  _Ribes grossularia_, i. 354-356, 376.
+  _Ribes rubrum_, i. 376.
+  RIBS, number and characters of, in fowls, i. 267;
+    characters of, in ducks, i. 283-284.
+  RICE, Imperial, of China, ii. 205;
+    Indian varieties of, ii. 256;
+    variety of, not requiring water, ii. 305.
+  RICHARDSON, H. D., on jaw-appendages in Irish pigs, i. 76;
+    management of pigs in China, i. 68;
+    occurrence of striped young in Westphalian pigs, i. 76;
+    on crossing pigs, ii. 95;
+    on interbreeding pigs, ii. 122;
+    on selection in pigs, ii. 194.
+  RICHARDSON, Sir John, observations on the resemblance between North
+      American dogs and wolves, i. 21-22;
+    on the burrowing of wolves, i. 27;
+    on the broad feet of dogs, wolves, and foxes in North America, i. 40;
+    on North American horses scraping away the snow, i. 53.
+  _Ricinus_, annual in England, ii. 305.
+  RIEDEL, on the "Bagadotte" pigeon, i. 141;
+    on the Jacobin pigeon, i. 154;
+    fertility of hybrid pigeons, i. 192.
+  RINDERPEST, ii. 378.
+  RISSO, on varieties of the orange, i. 336, ii. 308, 331.
+  RIVERS, Lord, on the selection of greyhounds, ii. 235.
+  RIVERS, Mr., persistency of characters in seedling potatoes, i. 331;
+    on the peach, i. 338, 339;
+    persistency of races in the peach and nectarine, i. 339, 340;
+    connexion between the peach and the nectarine, i. 340;
+    persistency of character in seedling apricots, i. 344;
+    origin of the plum, i. 345;
+    seedling varieties of the plum, i. 346;
+    persistency of character in seedling plums, i. 347;
+    bud-variation in the plum, i. 375;
+    plum, attacked by bullfinches, ii. 232;
+    seedling apples with surface-roots, i. 349;
+    variety of the apple found in a wood, ii. 260;
+    on roses, i. 366-367;
+    bud-variation in roses, i. 379-381;
+    production of Provence roses from seeds of the moss-rose, i. 380;
+    effect produced by grafting on the stock in jessamine, i. 394;
+    in the ash, i. 394;
+    on grafted hazels, i. 395;
+    hybridisation of a weeping thorn, ii. 18;
+    experiments with the seed of the weeping elm and ash, ii. 19;
+    variety of the cherry with curled petals, ii. 232.
+  RIVIERE, reproduction of _Oncidium Cavendishianum_, ii. 133.
+  ROBERTS, Mr., on inheritance in the horse, ii. 10.
+  ROBERTSON, Mr., on glandular-leaved peaches, i. 343.
+  ROBINET, on the silkworm, i. 301-304, ii. 197.
+  _Robinia_, ii. 274.
+  ROBSON, Mr., deficiencies of half-bred horses, ii. 11.
+  ROBSON, Mr., on the advantage of change of soil to plants, ii. 146-147;
+    on the growth of the verbena, ii. 273;
+    on broccoli, ii. 310.
+  ROCK pigeon, measurements of the, i. 134;
+    figured, i. 135.
+  RODENTS, sterility of, in captivity, ii. 152.
+  _Rodriguezia_, ii. 134, 135.
+  RODWELL, J., poisoning of horses by mildewed tares, ii. 337.
+  ROHILCUND, feral humped cattle in, i. 79.
+  ROLLE, F., on the history of the peach, ii. 308.
+  ROLLER-PIGEONS, Dutch, i. 151.
+  ROLLESTON, Prof., incisor teeth affected in form in cases of pulmonary
+      tubercle, ii. 332.
+  ROMANS, estimation of pigeons by, i. 205;
+    breeds of fowls possessed by, i. 231, 247.
+  {475}
+  ROOKS, pied, ii. 77.
+  _Rosa_, cultivated species of, i. 366.
+  _Rosa devoniensis_, graft-hybrid produced by, on the white Banksian rose,
+      i. 396.
+  _Rosa indica_ and _centifolia_, fertile hybrids of, i. 366.
+  _Rosa spinosissima_, history of the culture of, i. 367.
+  ROSELLINI, on Egyptian dogs, i. 17.
+  ROSES, i. 366-367;
+    origin of, i. 364;
+    bud-variation in, i. 379-381;
+    Scotch, doubled by selection, ii. 200;
+    continuous variation of, ii. 241;
+    effect of seasonal conditions on, ii. 273;
+    noisette, ii. 308;
+    galls of, ii. 284.
+  ROUENNAIS rabbit, i. 105.
+  ROULIN, on the dogs of Juan Fernandez, i. 27;
+    on South American cats, i. 46;
+    striped young pigs, i. 77;
+    feral pigs in South America, i. 78, ii. 33;
+    on Columbian cattle, i. 88, ii. 205, 226;
+    effects of heat on the hides of cattle in South America, i. 92;
+    fleece of sheep in the hot valleys of the Cordilleras, i. 98;
+    diminished fertility of these sheep, ii. 161;
+    on black-boned South American fowls, i. 258;
+    variation of the guinea-fowl in tropical America, i. 294;
+    frequency of striped legs in mules, ii. 42;
+    geese in Bogota, ii. 161;
+    sterility of fowls introduced into Bolivia, ii. 162.
+  ROY, M., on a variety of _Magnolia grandiflora_, ii. 308.
+  ROYLE, Dr., Indian varieties of the mulberry, i. 334;
+    on _Agave vivipara_, ii. 169;
+    variety of rice not requiring irrigation, ii. 305;
+    sheep from the Cape in India, ii. 306.
+  _Rubus_, pollen of, ii. 268.
+  RUDIMENTARY organs, i. 12, ii. 315-318.
+  RUFZ de Lavison, extinction of breeds of dogs in France, ii. 425.
+  RUMINANTS, general fertility of, in captivity, ii. 150.
+  RUMPLESS fowls, i. 230.
+  RUNTS, i. 142-144;
+    history of, i. 210;
+    lower jaws and skull figured, i. 164-165.
+  RUSSIAN or Himalayan rabbit, i. 108.
+  RUETIMEYER, Prof., dogs of the Neolithic period, i. 19;
+    horses of Swiss lake-dwellings, i. 49;
+    diversity of early domesticated horses i. 51;
+    pigs of the Swiss lake-dwellings, i. 65, 67-68;
+    on humped cattle, i. 80;
+    parentage of European breeds of cattle, i. 80, 81, ii. 427;
+    on "Niata" cattle, i. 89;
+    sheep of the Swiss lake-dwellings, i. 94, ii. 427;
+    goats of the Swiss lake-dwellings, i. 101;
+    absence of fowls in the Swiss lake-dwellings, i. 246;
+    on crossing cattle, ii. 98;
+    differences in the bones of wild and domesticated animals, ii. 279;
+    decrease in size of wild European animals, ii. 427.
+  RYE, wild, De Candolle's observations on, i. 313;
+    found in the Swiss lake-dwellings, i. 319;
+    common, preferred by hares and rabbits, ii. 232;
+    less variable than other cultivated plants, ii. 254.
+
+  SABINE, Mr., on the cultivation of _Rosa spinosissima_, i. 367;
+    on the cultivation of the dahlia, i. 369-370, ii. 261;
+    effect of foreign pollen on the seed-vessel in _Amaryllis vittata_, i.
+        400.
+  ST. ANGE, influence of the pelvis on the shape of the kidneys in birds,
+      ii. 344.
+  ST. DOMINGO, wild dogs of, i. 28;
+    bud-variation of dahlias in, i. 385.
+  ST. HILAIRE, Aug., milk furnished by cows in South America, ii. 300;
+    husked form of maize, i. 320.
+  ST. JOHN, C., feral cats in Scotland, i. 47;
+    taming of wild ducks, i. 278.
+  ST. VALERY apple, singular structure of the, i. 350;
+    artificial fecundation of the, i. 401.
+  ST. VITUS' Dance, period of appearance of, ii. 77.
+  SAGERET, origin and varieties of the cherry, i. 347-348;
+    origin of varieties of the apple, i. 350;
+    incapacity of the cucumber for crossing with other species, i. 359;
+    varieties of the melon, i. 360;
+    supposed twin-mongrel melon, i. 391;
+    crossing melons, ii. 108, 129;
+    on gourds, ii. 108;
+    effects of selection in enlarging fruit, ii. 217;
+    on the tendency to depart from type, ii. 241;
+    variation of plants in particular soils, ii. 278.
+  SALAMANDER, experiments on the, ii. 293, 341;
+    regeneration of lost parts in the, ii. 15, 376, 385.
+  _Salamandra cristata_, polydactylism in, ii. 14.
+  SALISBURY, Mr., on the production of nectarines by peach-trees, i. 341;
+    on the dahlia, i. 369-370.
+  _Salix_, intercrossing of species of, i. 336.
+  _Salix humilis_, galls of, ii. 282, 283.
+  SALLE, feral guinea-fowl in St. Domingo, i. 294.
+  SALMON, early breeding of male, ii. 384.
+  SALTER, Mr., on bud-variation in pelargoniums, i. 378;
+    in the Chrysanthemum, i. 379;
+    transmission of variegated leaves by seed, i. 383;
+    bud-variation by suckers in _Phlox_, i. 384;
+    application of selection to bud-varieties of plants, i. 411;
+    accumulative effect of changed conditions of life, ii. 262;
+    on the variegation of strawberry leaves, ii. 274.
+  SALTER, S. J., hybrids of _Gallus Sonneratii_ and the common fowl, i.
+      234, ii. 45;
+  {476}
+    crossing of races or species of rats, ii. 87-88.
+  SAMESREUTHER, on inheritance in cattle, ii. 10.
+  SANDFORD. _See_ DAWKINS.
+  SAP, ascent of the, ii. 296.
+  _Saponaria calabrica_, ii. 20.
+  SARDINIA, ponies of, i. 52.
+  SARS, on the development of the hydroida, ii. 368.
+  SATIATION of the stigma, i. 402-403.
+  _Saturnia pyri_, sterility of, in confinement, ii. 157.
+  SAUL, on the management of prize gooseberries, i. 356.
+  SAUVIGNY, varieties of the goldfish, i. 296.
+  SAVAGES, their indiscriminate use of plants as food, i. 307-310;
+    fondness of, for taming animals, ii. 160.
+  SAVI, effect of foreign pollen on maize, i. 400.
+  _Saxifraga geum_, ii. 166.
+  SAYZID MOHAMMED MUSARI, on carrier-pigeons, i. 141;
+    on a pigeon which utters the sound "Yahu," i. 155.
+  SCANDEROONS (pigeons), i. 142, 143.
+  SCANIA, remains of _Bos frontosus_ found in, i. 81.
+  SCAPULA, characters of, in rabbits, i. 123;
+    in fowls, i. 268;
+    in pigeons, i. 167;
+    alteration of, by disuse, in pigeons, i. 175.
+  SCARLET fever, ii. 276.
+  SCHAAFFHAUSEN, on the horses represented in Greek statues, ii. 213.
+  SCHACHT, H., on adventitious buds, ii. 384.
+  SCHLEIDEN, excess of nourishment a cause of variability, ii. 257.
+  SCHOMBURGK, Sir R., on the dogs of the Indians of Guiana, i. 19, 23, ii.
+      206;
+    on the musk duck, i. 182;
+    bud-variation in the Banana, i. 377;
+    reversion of varieties of the China rose in St. Domingo, i. 380;
+    sterility of tame parrots in Guiana, ii. 155;
+    on _Dendrocygna viduata_, ii. 157;
+    selection of fowls in Guiana, ii. 209.
+  SCHREIBERS, on _Proteus_, ii. 297.
+  _Sciuropterus volucella_, ii. 152.
+  _Sciurus palmarum_ and _cinerea_, ii. 152.
+  SCLATER, P. L., on _Asinus taeniopus_, i. 62, ii. 41;
+    on _Asinus indicus_, ii. 42;
+    striped character of young wild pigs, i. 70;
+    osteology of _Gallinula nesiotis_, i. 287;
+    on the black-shouldered peacock, i. 290;
+    on the breeding of birds in captivity, ii. 157.
+  SCHMERLING, Dr., varieties of the dog, found in a cave, i. 19.
+  SCOTCH fir, local variation of, i. 363.
+  SCOTCH kail and cabbage, cross between, ii. 98.
+  SCOTT, John, irregularities in the sex of the flowers of Maize, i. 321;
+    bud-variation in _Imatophyllum miniatum_, i. 385;
+    crossing of species of _Verbascum_, ii. 106-107;
+    experiments on crossing _Primulae_, ii. 109;
+    reproduction of orchids, ii. 133;
+    fertility of _Oncidium divaricatum_, ii. 164;
+    acclimatisation of the sweet pea in India, ii. 311;
+    number of seeds in _Acropera_ and _Gongora_, ii. 379.
+  SCOTT, Sir W., former range of wild cattle in Britain, i. 85.
+  SCROPE, on the Scotch deerhound, ii. 73, 121.
+  SEBRIGHT, Sir John, effects of close interbreeding in dogs, ii. 121;
+    care taken by, in selection of fowls, ii. 197.
+  _Secale cereale_, ii. 254.
+  SEDGWICK, W., effects of crossing on the female, i. 404;
+    on the "Porcupine-man," ii. 4;
+    on hereditary diseases, ii. 7;
+    hereditary affections of the eye, ii. 9, 78-79;
+    inheritance of polydactylism and anomalies of the extremities, ii.
+        13-14;
+    morbid uniformity in the same family, ii. 17;
+    on deaf-mutes, ii. 22;
+    inheritance of injury to the eye, ii. 24;
+    atavism in diseases and anomalies of structure, ii. 34;
+    non-reversion to night-blindness, ii. 36;
+    sexual limitation of the transmission of peculiarities in man, ii.
+        72-73;
+    on the effects of hard-drinking, ii. 289;
+    inherited baldness with deficiency of teeth, ii. 326-327;
+    occurrence of a molar tooth in place of an incisor, ii. 391;
+    diseases occurring in alternate generations, ii. 401.
+  SEDILLOT, on the removal of portions of bone, ii. 296.
+  SEEDS, early selection of, ii. 204;
+    rudimentary, in grapes, ii. 316;
+    relative position of, in the capsule, ii. 345.
+  SEEDS and buds, close analogies of, i. 411.
+  SEEMANN, B., crossing of the wolf and Esquimaux dog, i. 22.
+  SELBY, P. J., on the bud-destroying habits of the bullfinch, ii. 232.
+  SELECTION, ii. 192-249;
+    methodical, i. 214, ii. 194-210;
+    by the ancients and semi-civilised people, ii. 201-210;
+    of trifling characters, ii. 208-210;
+    unconscious, i. 214, 217, ii. 174, 210-217;
+    effects of, shown by differences in most valued parts, ii. 217-220;
+    produced by accumulation of variability, ii. 220-223;
+    natural, as affecting domestic productions, ii. 185-189, 224-233;
+    as the origin of species, genera and other groups, ii. 429-432;
+    circumstances favourable to, ii. 233-239;
+    tendency of towards extremes, ii. 239-242;
+  {477}
+    possible limit of, ii. 242;
+    influence of time on, ii. 243-244;
+    summary of subject, ii. 246-249;
+    effects of, in modifying breeds of cattle, i. 92, 93;
+    in preserving the purity of breeds of sheep, i. 99-100;
+    in producing varieties of pigeons, i. 213-218;
+    in breeding fowls, i. 232-233;
+    in the goose, i. 289;
+    in the canary, i. 295;
+    in the goldfish, i. 296;
+    in the silkworm, i. 300-301;
+    contrasted in cabbages and cereals, i. 323;
+    in the white mulberry, i. 334;
+    on gooseberries, i. 356;
+    applied to wheat, i. 317-318;
+    exemplified in carrots, &c., i. 326;
+    in the potato, i. 331;
+    in the melon, i. 360;
+    in flowering plants, i. 365;
+    in the hyacinth, i. 371;
+    applied to bud-varieties of plants, i. 411;
+    illustrations of, ii. 421-428.
+  SELECTION, sexual, ii. 75.
+  SELF-IMPOTENCE in plants, ii. 131-140;
+    in individual plants, ii. 136-138;
+    of hybrids, ii. 174.
+  SELWYN, Mr., on the Dingo, i. 26.
+  SELYS-LONGCHAMPS, on hybrid ducks, i. 190, ii. 46, 157;
+    hybrid of the hook-billed duck and Egyptian goose, i. 282.
+  SERINGE, on the St. Valery apple, i. 350.
+  SERPENT Melon, i. 360.
+  SERRES, Olivier de, wild poultry in Guiana, i. 237.
+  SESAMUM, white-seeded, antiquity of the, ii. 429.
+  _Setaria_, found in the Swiss lake-dwellings, i. 317.
+  SETTERS, degeneration of, in India, i. 38;
+    Youatt's remarks on, i. 41.
+  SEX, secondary characters of, latent, ii. 51-52;
+    of parents, influence of, on hybrids, ii. 267.
+  SEXUAL characters, sometimes lost in domestication, ii. 74.
+  SEXUAL limitation of characters, ii. 71-75.
+  SEXUAL peculiarities, induced by domestication in sheep, i. 95;
+    in fowls, i. 251-257;
+    transfer of, i. 255-257.
+  SEXUAL variability in pigeons, i. 161-162.
+  SEXUAL selection, ii. 75.
+  SHADDOCK, i. 335.
+  SHAILER, Mr., on the moss-rose, i. 379-380.
+  SHANGHAI fowls, i. 227.
+  SHANGHAI sheep, their fecundity, i. 97.
+  SHAN ponies, striped, i. 58.
+  SHEEP, disputed origin of, i. 94;
+    early domestication of, i. 94;
+    large-tailed, i. 94, 95, 98, ii. 279;
+    variations in horns, mammae and other characters of, i. 95;
+    sexual characters of, induced by domestication, i. 95, 96;
+    adaptation of, to climate and pasture, i. 96, 97;
+    periods of gestation of, i. 97;
+    effect of heat on the fleece of, i. 98-99, ii. 278;
+    effect of selection on, i. 99-101;
+    "ancon" or "otter" breeds of, i. 17, 92, 100;
+    "Mauchamp-merino," i. 100-101;
+    cross of German and merino, ii. 85-89;
+    black, of the Tarentino, ii. 227;
+    Karakool, ii. 278;
+    Jaffna, with callosities on the knees, ii. 302;
+    Chinese, ii. 315;
+    Danish, of the bronze period, ii. 427;
+    polydactylism in, ii. 14;
+    occasional production of horns in hornless breeds of, ii. 30;
+    reversion of colour in, ii. 30;
+    influence of male, on offspring, ii. 68;
+    sexual differences in, ii. 73;
+    influence of crossing or segregation on, ii. 86, 95-96, 102-103;
+    interbreeding of, ii. 119-120;
+    effect of nourishment on the fertility of, ii. 111-112;
+    diminished fertility of, under certain conditions, ii. 161;
+    unconscious selection of, ii. 213;
+    natural selection in breeds of, ii. 224, 225, 227;
+    reduction of bones in, ii. 242;
+    individual differences of, ii. 251;
+    local changes in the fleece of, in England, ii. 278;
+    partial degeneration of, in Australia, ii. 278;
+    with numerous horns, ii. 291;
+    correlation of horns and fleece in, ii. 326;
+    feeding on flesh, ii. 303;
+    acclimatisation of, ii. 305-306;
+    mountain, resistance of, to severe weather, ii. 312;
+    white, poisoned by _Hypericum crispum_, ii. 337.
+  SHEEP dogs resembling wolves, i. 24.
+  SHELLS, sinistral and dextral, ii. 53.
+  SHERIFF, Mr. new varieties of wheat, i. 315, 317;
+    on crossing wheat, ii. 104-105;
+    continuous variation of wheat, ii. 241.
+  SIAM, cats of, i. 47; horses of, i. 53.
+  SHIRLEY, E. P., on the fallow-deer, ii. 103, 120.
+  SHORT, D., hybrids of the domestic cat and _Felis ornata_, i, 45.
+  SIBERIA, northern range of wild horses in, i. 52.
+  SICHEL, J., on the deafness of white cats with blue eyes, ii. 329.
+  SIDNEY, S., on the pedigrees of pigs, ii. 3;
+    on cross-reversion in pigs, ii. 35;
+    period of gestation in the pig, i. 74;
+    production of breeds of pigs by intercrossing, i. 78, 95;
+    fertility of the pig, ii. 112;
+    effects of interbreeding on pigs, ii. 121-122;
+    on the colours of pigs, ii. 210, 229.
+  SIEBOLD, on the sweet potato, ii. 309.
+  SIEBOLD, von Carl, on parthenogenesis, ii. 364.
+  _Silene_, contabescence in, ii. 166.
+  SILK-FOWLS, i. 230, ii. 67, 69.
+  {478}
+  SILK-MOTH, Arrindy, ii. 306, 312;
+    Tarroo, ii. 157.
+  SILK-MOTHS, i. 300-304;
+    domesticated species of, i. 300;
+    history of, _ibid._;
+    causes of modification in, i. 300-301;
+    differences presented by, i. 301-304;
+    crossing of, ii. 98;
+    disease in, ii. 228;
+    effects of disuse of parts in, ii. 298;
+    selection practised with, ii. 197, 199;
+    variation of, ii. 236;
+    parthenogenesis in, ii. 364.
+  SILKWORMS, variations of, i. 301-302;
+    yielding white cocoons, less liable to disease, ii. 336.
+  SILVER-GREY rabbit, i. 108, 111, 120.
+  SIMONDS, J. B., period of maturity in various breeds of cattle, i. 87;
+    differences in the periods of dentition in sheep, i. 96;
+    on the teeth in cattle, sheep, &c., ii. 322;
+    on the breeding of superior rams, ii. 196.
+  SIMON, on the raising of eggs of the silk-moth in China, ii. 197.
+  SIMPSON, Sir J., regenerative power of the human embryo, ii. 15.
+  _Siredon_, breeding in the branchiferous stage, ii. 384.
+  SISKIN, breeding in captivity, ii. 154.
+  _Sivatherium_, resemblance of the, to Niata cattle, i. 89.
+  SIZE, difference of, an obstacle to crossing, ii. 101.
+  SKIN, and its appendages, homologous, ii. 325;
+    hereditary affections of the, ii. 79.
+  SKIRVING, R. S., on pigeons settling on trees in Egypt, i. 181.
+  SKULL, characters of the, in breeds of dogs, i. 34;
+    in breeds of pigs, i. 71;
+    in rabbits, i. 116-120, 127;
+    in breeds of pigeons, i. 163-165;
+    in breeds of fowls, i. 260-266;
+    in ducks, i. 282-283.
+  SKULL and horns, correlation of the, ii. 333.
+  SKYLARK, ii. 154.
+  SLEEMAN, on the Cheetah, ii. 151.
+  SLOE, i. 345.
+  SMALL-POX, ii. 378.
+  SMITER (pigeon), i. 156.
+  SMITH, Sir A., on Caffrarian cattle, i. 88;
+    on the use of numerous plants as food in South Africa, i. 307.
+  SMITH, Colonel Hamilton, on the odour of the jackal, i. 30;
+    on the origin of the dog, i. 16;
+    wild dogs in St. Domingo, i. 28;
+    on the Thibet mastiff and the alco, i. 28-29;
+    development of the fifth toe in the hind feet of mastiffs, i. 35;
+    differences in the skull of dogs, i. 34;
+    history of the pointer, i. 42;
+    on the ears of the dog, ii. 301;
+    on the breeds of horses, i. 49;
+    origin of the horse, i. 51;
+    dappling of horses, i. 55;
+    striped horses in Spain, i. 58;
+    original colour of the horse, i. 60;
+    on horses scraping away snow, i. 52;
+    on _Asinus hemionus_, ii. 43;
+    feral pigs of Jamaica, i. 77-78.
+  SMITH, Sir J. E., production of nectarines and peaches by the same tree,
+      i. 340;
+    on _Viola amoena_, i. 368;
+    sterility of _Vinca minor_ in England, ii. 170.
+  SMITH, J., development of the ovary in _Bonatea speciosa_, by irritation
+      of the stigma, i. 403.
+  SMITH, N. H., influence of the bull "Favourite" on the breed of
+      Short-horn cattle, ii. 65.
+  SMITH, W., on the inter-crossing of strawberries, i. 352.
+  SNAKE-RAT, ii. 87, 88.
+  SNAKES, form of the viscera in, ii. 344.
+  SNAPDRAGON, bud-variation in, i. 381;
+    non-inheritance of colour in, ii. 21;
+    peloric, crossed with the normal form, ii. 70, 93;
+    asymmetrical variation of the, ii. 322.
+  SOIL, adaptation of plums to, i. 346;
+    influence of, on the zones of pelargoniums, i. 366;
+    on roses, i. 367;
+    on the variegation of leaves, i. 383;
+    advantages of change of, ii. 146-148.
+  SOIL and climate, effects of, on strawberries, i. 353.
+  _Solanum_, non-intercrossing of species of, ii. 91.
+  _Solanum tuberosum_, i. 330-331.
+  SOLID-HOOFED pigs, i. 75.
+  SOLOMON, his stud of horses, i. 55.
+  SOMERVILLE, Lord, on the fleece of Merino sheep, i. 99;
+    on crossing sheep, ii. 120;
+    on selection of sheep, ii. 195;
+    diminished fertility of Merino sheep brought from Spain, ii. 161.
+  SOOTY fowls, i. 230, 256.
+  SOTO, Ferdinand de, on the cultivation of native plants in Florida, i.
+      312.
+  _Sorghum_, i. 371.
+  SPAIN, hawthorn monogynous in, i. 364.
+  SPALLANZANI, on feral rabbits in Lipari, i. 113;
+    experiments on salamanders, ii. 15, 293, 385;
+    experiments in feeding a pigeon with meat, ii. 304.
+  SPANIELS, in India, i. 38;
+    King Charles's, i. 41;
+    degeneration of, caused by interbreeding, ii. 121.
+  SPANISH fowls, i. 227, 250, 253;
+    figured, i. 226;
+    early development of sexual characters in, i. 250, 251;
+    furcula of, figured, i. 268.
+  SPECIES, difficulty of distinguishing from varieties, i. 4;
+    conversion of varieties into, i. 5;
+    origin of, by natural selection, ii. 414-415;
+    by mutual sterility of varieties, ii. 185-189.
+  {479}
+  SPENCER, Lord, on selection in breeding, ii. 195.
+  SPENCER, Herbert, on the "survival of the fittest," i. 6;
+    increase of fertility by domestication, ii. 111;
+    on life, ii. 148, 177;
+    changes produced by external conditions, ii. 281;
+    effects of use on organs, ii. 295, 296;
+    ascent of the sap in trees, ii. 296;
+    correlation exemplified in the Irish elk, ii. 333-334;
+    on "physiological units," ii. 375;
+    antagonism of growth and reproduction, ii. 384;
+    formation of ducts in plants, ii. 300.
+  SPERMATOPHORES of the cephalopoda, ii. 383.
+  SPERMATOZOIDS, ii. 363-364;
+    apparent independence of, in insects, ii. 384.
+  SPHINGIDAE, sterility of, in captivity, ii. 157.
+  SPINOLA, on the injurious effect produced by flowering buckwheat on white
+      pigs, ii. 337.
+  SPITZ dog, i. 31.
+  SPOONER, W. C., cross-breeding of sheep, i. 100, ii. 95-96, 120;
+    on the effects of crossing, ii. 96-97;
+    on crossing cattle, ii. 118;
+    individual sterility, ii. 162.
+  SPORES, reproduction of abnormal forms by, i. 383.
+  SPORTS, i. 373; in pigeons, i. 213.
+  SPOT pigeon, i. 156, 207.
+  SPRENGEL, C. K., on dichogamous plants, ii. 90;
+    on the hollyhock, ii. 107;
+    on the functions of flowers, ii. 175.
+  SPROULE, Mr., inheritance of cleft-palate and hare-lip, ii. 24.
+  SPURS, of fowls, i. 255;
+    development of, in hens, ii. 318.
+  SQUASHES, i. 357.
+  SQUINTING, hereditary, ii. 9.
+  SQUIRRELS, generally sterile in captivity, ii. 152.
+  SQUIRRELS, flying, breeding in confinement, ii. 152.
+  "STAARHALSIGE Taube," i. 161.
+  STAG, one-horned, supposed heredity of character in, ii. 12;
+    degeneracy of, in the Highlands, ii. 208.
+  STAMENS, occurrence of rudimentary, ii. 316;
+    conversion of, into pistils, i. 365;
+    into petals, ii. 392.
+  _Staphylea_, ii. 168.
+  STEENSTRUP, Prof., on the dog of the Danish Middens, i. 18;
+    on the obliquity of flounders, ii. 53.
+  STEINAN, J., on hereditary diseases, ii. 7, 79.
+  STERILITY, in dogs, consequent on close confinement, i. 32;
+    comparative, of crosses, ii. 103, 104;
+    from changed conditions of life, ii. 148-165;
+    occurring in the descendants of wild animals bred in captivity, ii.
+        160;
+    individual, ii. 162;
+    resulting from propagation by buds, cuttings, bulbs, &c., ii. 169;
+    in hybrids, ii. 178-180, 386, 410-411;
+    in specific hybrids of pigeons, i. 193;
+    as connected with natural selection, ii. 185-189.
+  STERNUM, characters of the, in rabbits, i. 123;
+    in pigeons, i. 167, 174-175;
+    in fowls, i. 268, 273;
+    effects of disuse on the, i. 174-175, 273.
+  STEPHENS, J. F., on the habits of the Bombycidae, i. 303.
+  STEWART, H., on hereditary disease, ii. 79.
+  STIGMA, variation of the, in cultivated Cucurbitaceae, i. 359;
+    satiation of the, i. 402-403.
+  STOCKS, bud-variation in, i. 381;
+    effect of crossing upon the colour of the seed of, i. 398-399;
+    true by seed, ii. 20;
+    crosses of, ii. 93;
+    varieties of, produced by selection, ii. 219;
+    reversion by the upper seeds in the pods of, ii. 347-348.
+  STOCKHOLM, fruit-trees of, ii. 307.
+  STOKES, Prof., calculation of the chance of transmission of abnormal
+      peculiarities in man, ii. 5.
+  STOLONS, variations in the production of, by strawberries, i. 353.
+  STOMACH, structure of the, affected by food, ii. 302.
+  STONE in the bladder, hereditary, ii. 8, 79.
+  STRAWBERRIES, i. 351-354;
+    remarkable varieties of, i. 352-353;
+    hautbois, dioecious, i. 353;
+    selection in, ii. 200;
+    mildew of, ii. 228;
+    probable further modification of, ii. 243;
+    variegated, effects of soil on, ii. 274.
+  STRICKLAND, A., on the domestication of _Anser ferus_, i. 287;
+    on the colour of the bill and legs in geese, i. 288.
+  _Strictoenas_, i. 183.
+  STRIPES on young of wild swine, i. 76;
+    of domestic pigs of Turkey, Westphalia, and the Zambesi, i. 76-77;
+    of feral swine of Jamaica and New Granada, i. 77;
+    of fruit and flowers, i. 400, ii. 37;
+    in horses, i. 56-60;
+    in the ass, i. 62-63;
+    production of, by crossing species of Equidae, ii. 42-43.
+  _Strix grallaria_, ii. 302.
+  _Strix passerina_, ii. 154.
+  "STRUPP-TAUBE," i. 155.
+  STRUTHERS, Mr., osteology of the feet in solid-hoofed pigs, i. 75;
+    on polydactylism, ii. 13-14.
+  STURM, prepotency of transmission of characters in sheep and cattle, ii.
+      66;
+    absorption of the minority in crossed races, ii. 88;
+    correlation of twisted horns and curled wool in sheep, ii. 326.
+  {480}
+  SUB-SPECIES, wild, of _Columba livia_ and other pigeons, i. 204.
+  SUCCESSION, geological, of organisms, i. 11.
+  SUCKERS, bud-variation by, i. 384.
+  SUGAR cane, sterility of, in various countries, ii. 169;
+    white, liability of, to disease, ii. 228, 336.
+  SUICIDE, hereditary tendency to, ii. 7, 78.
+  SULIVAN, Admiral, on the horses of the Falkland Islands, i. 53;
+    wild pigs of the Falkland Islands, i. 77;
+    feral cattle of the Falkland Islands, i. 86, 102;
+    feral rabbits of the Falkland Islands, i. 112.
+  SULTAN fowl, i. 228, 255.
+  _Sus indica_, i. 65, 67-70, ii. 110.
+  _Sus pliciceps_, i. 69 (figured).
+  _Sus scrofa_, i. 65, 66, ii. 110.
+  _Sus scrofa palustris_, i. 68.
+  _Sus vittatus_, i. 67.
+  SWALLOWS, a breed of pigeons, i. 156.
+  SWAYNE, Mr., on artificial crossing of varieties of the pea, i. 397.
+  SWEET Peas, ii. 91;
+    crosses of, ii. 93, 94;
+    varieties of, coming true by seed, ii. 20;
+    acclimatisation of, in India, ii. 311.
+  SWEET William, bud-variation in, i. 381.
+  SWINHOE, R., on Chinese pigeons, i. 28, 206;
+    on striped Chinese horses, i. 59.
+  SWITZERLAND, ancient dogs of, i. 19;
+    pigs of, in the Neolithic period, i. 67-68;
+    goats of, i. 101.
+  SYCAMORE, pale-leaved variety of the, ii. 330.
+  SYKES, Colonel, on a Pariah dog with crooked legs, i. 17;
+    on small Indian asses, i. 62;
+    on _Gallus Sonneratii_, i. 233;
+    on the voice of the Indian Kulm cock, i. 259;
+    fertility of the fowl in most climates, ii. 161.
+  SYMMETRY, hereditary departures from, ii. 12.
+  _Symphytum_, variegated, i. 384.
+  SYPHILIS, hereditary, ii. 332.
+  SYRIA, asses of, i. 62.
+  _Syringa persica_, _chinensis_, and _vulgaris_, ii. 164.
+
+  TACITUS, on the care taken by the Celts in breeding animals, ii. 202.
+  _Tagetes signata_, dwarf variety of, ii. 20.
+  TAHITI, varieties of cultivated plants in, ii. 256.
+  TAIL, occasional development of, in man, ii. 57;
+    never curled in wild animals, ii. 301;
+    rudimentary in Chinese sheep, ii. 315.
+  TAIL-FEATHERS, numbers of, in breeds of pigeons, i. 158-159;
+    peculiarities of, in cocks, i. 254-255;
+    variability of, in fowls, i. 258;
+    curled, in _Anas boschas_, and tame drakes, i. 280.
+  TALENT, hereditary, ii. 7.
+  TANKERVILLE, Earl of, on Chillingham cattle, i. 84, ii. 119.
+  TANNER, Prof., effects of disuse of parts in cattle, ii. 299.
+  TAPIR, sterility of the, in captivity, ii. 150.
+  TARGIONI-TOZZETTI, on cultivated plants, i. 306;
+    on the vine, i. 332;
+    varieties of the peach, i. 342;
+    origin and varieties of the plum, i. 345;
+    origin of the cherry, i. 347;
+    origin of roses, i. 366.
+  TARSUS, variability of the, in fowls, i. 259;
+    reproduction of the, in a thrush, ii. 15.
+  TARTARS, their preference for spiral-horned sheep, ii. 209.
+  TAVERNIER, abundance of pigeons in Persia, i. 205.
+  _Taxus baccata_, ii. 18.
+  TEEBAY, Mr., reversion in fowls, ii. 38.
+  TEETH, number and position of, in dogs, i. 34;
+    deficiency of, in naked Turkish dogs, i. 35;
+    period of appearance of, in breeds of dogs, i. 35;
+    precocity of, in highly bred animals, ii. 322;
+    correlation of, with hair, ii. 326;
+    double row of, with redundant hair, in Julia Pastrana, ii. 328;
+    affected in form by hereditary syphilis and by pulmonary tubercle, ii.
+        332;
+    fusion of, ii. 341;
+    developed on the palate, ii. 391.
+  TEGETMEIER, Mr., on a cat with monstrous teeth, i. 48;
+    on a swift-like pigeon, i. 157;
+    naked young of some pigeons, i. 170;
+    fertility of hybrid pigeons, i. 192;
+    on white pigeons, ii. 230;
+    reversion in crossed breeds of fowls, i. 239-244;
+    chicks of the white silk-fowl, i. 249;
+    development of the cranial protuberance in Polish fowls, i. 250;
+    on the skull in the Polish fowl, i. 257, 262;
+    on the intelligence of Polish fowls, i. 264;
+    correlation of the cranial protuberance and crest in Polish fowls, i.
+        274;
+    development of the web in the feet of Polish fowls, i. 259;
+    early development of several peculiarities in Spanish cocks, i. 250;
+    on the comb in Spanish fowls, i. 253;
+    on the Spanish fowl, ii. 306;
+    varieties of game-fowls, i. 252;
+    pedigrees of game-fowls, ii. 3;
+    assumption of female plumage by a game cock, i. 253;
+    natural selection in the game cock, ii. 225;
+    pugnacity of game hens, i. 256;
+    length of the middle toe in Cochin fowls, i. 259;
+    origin of the Sebright bantam, ii. 54;
+    differences in the size of fowls, i. 257;
+    effect of crossing in fowls, i. 258, ii. 96;
+    effects of interbreeding in fowls, ii. 124-125;
+    incubation by mongrels of non-sitting races of fowls, ii. 44;
+    inverse correlation of crest and comb in fowls, i. 274;
+  {481}
+    occurrence of pencilled feathers in fowls, ii. 40;
+    on a variety of the goose from Sebastopol, i. 289;
+    on the fertility of the peahen, ii. 112;
+    on the intercrossing of bees, ii. 126.
+  TEMMINCK, origin of domestic cats, i. 43;
+    origin of domestic pigeons, i. 180;
+    on _Columba guinea_, i. 182;
+    on _Columba leucocephala_, i. 183;
+    asserted reluctance of some breeds of pigeons to cross, i. 192;
+    sterility of hybrid turtle-doves, i. 193;
+    variations of _Gallus bankiva_, i. 235;
+    on a buff-coloured breed of Turkeys, i. 293;
+    number of eggs laid by the peahen, ii. 112;
+    breeding of Guans in captivity, ii. 156;
+    behaviour of grouse in captivity, _ibid._;
+    sterility of the partridge in captivity, _ibid._
+  TENDRILS in Cucurbitaceae, i. 358, ii. 316.
+  TENNENT, Sir J. E., on the goose, i. 287;
+    on the growth of the apple in Ceylon, ii. 277;
+    on the Jaffna sheep, ii. 302.
+  _Teredo_, fertilisation in, ii. 363.
+  TERRIERS, wry-legged, ii. 245;
+    white, subject to distemper, ii. 336.
+  TESCHEMACHER, on a husked form of maize, i. 320.
+  TESSIER, on the period of gestation of the dog, i. 29;
+    of the pig, i. 74;
+    in cattle, i. 87;
+    experiments on change of soil, ii. 147.
+  _Tetrao_, breeding of species of, in captivity, ii. 156.
+  _Tetrapteryx paradisea_, ii. 156.
+  _Teucrium campanulatum_, pelorism in, ii. 345.
+  TEXAS, feral cattle in, i. 85.
+  THEOGNIS, his notice of the domestic fowl, i. 246.
+  THEOPHRASTUS, his notice of the peach, ii. 308.
+  _Thesium_, ii. 284.
+  THOMPSON, Mr., on the peach and nectarine, i. 342;
+    on the varieties of the apricot, i. 344;
+    classification of varieties of cherries, i. 347-348;
+    on the "Sister ribston-pippin," i. 350;
+    on the varieties of the gooseberry, i. 354, 355.
+  THOMPSON, William, on the pigeons of Islay, i. 184;
+    feral pigeons in Scotland, i. 190;
+    colour of the bill and legs in geese, i. 288;
+    breeding of _Tetrao scotius_ in captivity, ii. 156;
+    destruction of black-fowls by the osprey, ii. 230.
+  THOMPSON, Prof. W., on the obliquity of the flounder, ii. 53.
+  THORNS, reconversion of, into branches, in pear trees, ii. 318.
+  THORN, grafting of early and late, i. 363;
+    Glastonbury, i. 364.
+  THRUSH, asserted reproduction of the tarsus in a, ii. 15.
+  _Thuja pendula_ or _filiformis_, a variety of _T. orientalis_, i. 362.
+  THURET, on the division of the zoospores of an alga, ii. 378.
+  THWAITES, G. H., on the cats of Ceylon, i. 46;
+    on a twin seed of _Fuchsia coccinea_ and _fulgens_, i. 391.
+  TIBURTIUS, experiments in rearing wild ducks, i. 278.
+  TIGER, rarely fertile in captivity, ii. 150, 151.
+  _Tigridia conchiflora_, bud-variation in, i. 386.
+  TIME, importance of, in the production of races, ii. 243.
+  TINZMANN, self-impotence in the potato, ii. 137.
+  TISSUES, affinity of, for special organic substances, ii. 380.
+  TITMICE, destructive to thin-shelled walnuts, i. 356;
+    attacking nuts, i. 357;
+    attacking peas, ii. 231.
+  TOBACCO, crossing of varieties of, ii. 108;
+    cultivation of in Sweden, ii. 307.
+  TOBOLSK, red-coloured cats of, i. 47.
+  TOES, relative length of, in fowls, i. 259;
+    development of fifth in dogs, ii. 317.
+  TOLLET, Mr., his selection of cattle, ii. 199.
+  TOMATO, ii. 91.
+  TOMTITS. See _Titmice_.
+  TONGUE, relation of, to the beak in pigeons, i. 168.
+  TOOTH, occurrence of a molar, in place of an incisor, ii. 391.
+  "TORFSCHWEIN,"  i. 68.
+  TRAIL, R., on the union of half-tubers of different kinds of potatoes, i.
+      395.
+  TREES, varieties of, suddenly produced, i. 361;
+    weeping or pendulous, i. 361;
+    fastigate or pyramidal, i. 361;
+    with variegated or changed foliage, i. 362;
+    early or late in leaf, i. 362-363;
+    forest, non-application of selection to, ii. 237.
+  "TREMBLEUR" (pigeons), i. 146.
+  TREMBLEY, on reproduction in Hydra, ii. 359.
+  "TREVOLTINI" silkworms, i. 301-302.
+  _Trichosanthes anguina_, i. 360.
+  TRICKS, inheritance of, ii. 6-7, 395.
+  _Trifolium minus_ and _repens_, ii. 164.
+  TRIMORPHIC plants, conditions of reproduction in, ii. 181-184.
+  TRISTRAM, H. B., selection of the dromedary, ii. 205-206.
+  _Triticum dicoccum_, i. 319.
+  _Triticum monococcum_, i. 319.
+  _Triticum spelta_, i. 319.
+  _Triticum turgidum_, i. 319.
+  _Triticum vulgare_, wild in Asia, i. 312.
+  {482}
+  TRITON, breeding in the branchiferous stage, ii. 384.
+  "TROMMEL-TAUBE," i. 154.
+  "TRONFO" pigeon, i. 144.
+  _Tropaeolum_, ii. 38.
+  _Tropaeolum minus_ and _majus_, reversion in hybrids of, i. 392.
+  TROUBETZKOY, Prince, experiments with pear-trees at Moscow, ii. 307.
+  TROUSSEAU, Prof., pathological resemblance of twins, ii. 252.
+  TRUMPETER pigeon, i. 154;
+    known in 1735, i. 207.
+  TSCHARNER, H. A. de, graft-hybrid produced by inosculation in the vine,
+      i. 395.
+  TSCHUDI, on the naked Peruvian dog, i. 23;
+    extinct varieties of maize from Peruvian tombs, i. 320, ii. 425.
+  TUBERS, bud-variation by, i. 384-385.
+  TUCKERMAN, Mr., sterility of _Carex rigida_, ii. 170.
+  TUFTED ducks, i. 281.
+  TULIPS, variability of, i. 370;
+    bud-variation in, i. 385-386;
+    influence of soil in "breaking," i. 385.
+  TUMBLER pigeon, i. 150-153;
+    short-faced, figured, i. 152;
+    skull figured, i. 163;
+    lower jaw figured, i. 165;
+    scapula and furcula figured, i. 167;
+    early known in India, i. 207;
+    history of, i. 209;
+    sub-breeds of, i. 220;
+    young unable to break the egg-shell, ii. 226;
+    probable further modification of, ii. 242.
+  "TUEMMLER" (pigeons), i. 150.
+  TUMOURS, ovarian, occurrence of hairs and teeth in, ii. 370;
+    polypoid, origin of, ii. 381.
+  "TUERKISCHE TAUBE," i. 139.
+  TURBIT (pigeon), i. 148.
+  TURKEY, domestic, origin of, i. 292-293;
+    crossing of with North American wild Turkey, i. 292-293;
+    breeds of, i. 293;
+    crested white cock, i. 293;
+    wild, characters of, i. 293-294;
+    degeneration of, in India, i. 294, ii. 278;
+    failure of eggs of, in Delhi, ii. 161;
+    feral on the Parana, i. 190;
+    change produced in by domestication, ii. 262.
+  TURKEY, striped young pigs in, i. 76.
+  TURNER (pigeon), i. 156.
+  TURNER, W., on compensation in arteries and veins, ii. 300;
+    on cells, ii. 370.
+  TURNIPS, origin of, i. 325;
+    reversion in, ii. 31;
+    run wild, ii. 33;
+    crosses of, ii. 93, 96;
+    Swedish, preferred by hares, ii. 232;
+    acclimatisation of, in India, ii. 311.
+  TURNSPIT, on an Egyptian monument, i. 17;
+    crosses of the, ii. 92.
+  TURTLE-DOVE, white and coloured, crossing of, ii. 92.
+  _Turtur auritus_, hybrids of, with _T. cambayensis_ and _T. suratensis_,
+      i. 194.
+  _Turtur risorius_, crossing of, with the common pigeon, i. 193;
+    hybrid of, with _T. vulgaris_, _ibid._
+  _Turtur suratensis_, sterile hybrids of, with _T. vulgaris_, i. 193;
+    hybrids of, with _T. auritus_, i. 194.
+  _Turtur vulgaris_, crossing of, with the common pigeon, i. 193;
+    hybrid of, with _T. risorius_, _ibid._;
+    sterile hybrids of, with _T. suratensis_ and _Ectopistes migratorius_,
+        _ibid._
+  TUSKS of wild and domesticated pigs, i. 76, 77.
+  _Tussilago farfara_, variegated, i. 384.
+  TWIN-SEED _Fuchsia coccinea_ and _fulgens_, i. 391.
+  TYERMAN, B., on the pigs of the Pacific islands, i. 70, ii. 87;
+    on the dogs of the Pacific islands, ii. 87.
+  TYLOR, Mr., on the prohibition of consanguineous marriages, ii. 122-123.
+
+  UDDERS, development of the, ii. 300.
+  _Ulex_, double-flowered, ii. 167.
+  _Ulmus campestris_ and _effusa_, hybrids of, ii. 130.
+  UNIFORMITY of character, maintained by crossing, ii. 85-90.
+  UNITS of the body, functional independence of the, ii. 368-371.
+  UNITY or plurality of origin of organisms, i. 13.
+  UPAS poison, ii. 380.
+  UREA, secretion of, ii. 380.
+  USE and disuse of parts, effects of, ii. 295-303, 352-353, 418-419;
+    in rabbits, i. 124-128;
+    in ducks, i. 284-286.
+  UTILITY, considerations of, leading to uniformity, ii. 241.
+
+  VALENTIN, experimental production of double monsters by, ii. 340.
+  _Vallota_, ii. 139.
+  VAN BECK, Barbara, a hairy-faced woman, ii. 4.
+  VAN MONS on wild fruit-trees, i. 312, ii. 260;
+    production of varieties of the vine, i. 333;
+    correlated variability in fruit-trees, ii. 330;
+    production of almond-like fruit by peach-seedlings, i. 339.
+  _Vanessa_, species of, not copulating in captivity, ii. 157.
+  VARIABILITY, i. 4, ii. 371-373, 394-397, 406-420;
+    causes of, ii. 250-270;
+    correlated, ii. 319-338, 353-355, 419-420;
+    law of equable, ii. 351-352;
+    necessity of, for selection, ii. 192;
+    of selected characters, ii. 238-239;
+    of multiple homologous parts, ii. 342.
+  {483}
+  VARIATION, laws of, ii. 293-356;
+    continuity of, ii. 241;
+    possible limitation of, ii. 242, 416-417;
+    in domestic cats, i. 45-48;
+    origin of breeds of cattle by, i. 88;
+    in osteological characters of rabbits, i. 115-130;
+    of important organs, i. 359;
+    analogous or parallel, i. 348-352;
+    in horses, i. 55;
+    in the horse and ass, i. 64;
+    in fowls, i. 243-246;
+    in geese, i. 288;
+    exemplified in the production of fleshy stems in cabbages, &c., i. 326;
+    in the peach, nectarine, and apricot, i. 342, 344;
+    individual, in wheat, i. 314.
+  VARIEGATION of foliage, i. 383, ii. 167-168.
+  VARIETIES and species, resemblance of, i. 4, ii. 411-413;
+    conversion of, into species, i. 5;
+    abnormal, ii. 413;
+    domestic, gradually produced, ii. 414.
+  VARRO, on domestic ducks, i. 277;
+    on feral fowls, ii. 33;
+    crossing of the wild and domestic ass, ii. 206.
+  VASEY, Mr., on the number of sacral vertebrae in ordinary and humped
+      cattle, i. 79;
+    on Hungarian cattle, i. 80.
+  VAUCHER, sterility of _Ranunculus ficaria_ and _Acorus calamus_, ii. 170.
+  VEGETABLES, cultivated, reversion in, ii. 31-32;
+    European, culture of, in India, ii. 168-169.
+  VEITH, Mr., on breeds of horses, i. 49.
+  _Verbascum_, intercrossing of species of, i. 336, ii. 93, 105-107;
+    reversion in hybrids of, i. 392;
+    contabescent, wild plants of, ii. 165;
+    villosity in, ii. 277.
+  _Verbascum austriacum_, ii. 136.
+  _Verbascum blattaria_, ii. 105-106.
+  _Verbascum lychnitis_, ii. 105-106, 136.
+  _Verbascum nigrum_, ii. 136.
+  _Verbascum phoeniceum_, ii. 107, 137;
+    variable duration of, ii. 305.
+  _Verbascum thapsus_, ii. 106.
+  VERBENAS, origin of, i. 364;
+    white, liability of, to mildew, ii. 228, 336;
+    scorching of dark, ii. 229, 336;
+    effect of changed conditions of life on, ii. 273.
+  VERLOT, on the darkleaved Barberry, i. 362;
+    inheritance of peculiarities of foliage in trees, i. 362;
+    production of _Rosa cannabifolia_ by bud-variation from _R. alba_, i.
+        381;
+    bud-variation in _Aralia trifoliata_, i. 382;
+    variegation of leaves, i. 383;
+    colours of tulips, i. 386;
+    uncertainty of inheritance, ii. 18;
+    persistency of white flowers, ii. 20;
+    peloric flowers of _Linaria_, ii. 58;
+    tendency of striped flowers to uniformity of colour, ii. 70;
+    non-intercrossing of certain allied plants, ii. 91;
+    sterility of _Primulae_ with coloured calyces, ii. 166;
+    on fertile proliferous flowers, _ibid._;
+    on the Irish yew, ii. 241;
+    differences in the _Camellia_, ii. 251;
+    effect of soil on the variegated strawberry, ii. 274;
+    correlated variability in plants, ii. 330.
+  _Verruca_, ii. 53, 400.
+  VERTEBRAE, characters of, in rabbits, i. 120-122;
+    in ducks, i. 283-284;
+    number and variations of, in pigeons, i. 165-166;
+    number and characters of, in fowls, i. 266-268;
+    variability of number of, in the pig, i. 74.
+  VERTUCH, see Putsche.
+  "VERUGAS," ii. 276.
+  VESPUCIUS, early cultivation in Brazil, i. 311.
+  VIBERT'S experiments on the cultivation of the vine from seed, i. 332.
+  _Viburnum opulus_, ii. 185, 316.
+  _Vicia sativa_, leaflet converted into a tendril in, ii. 392.
+  VICUNAS, selection of, ii. 207.
+  VILLOSITY of plants, influenced by dryness, ii. 277.
+  VILMORIN, cultivation of the wild carrot, i. 326, ii. 217;
+    colours of tulips, i. 386;
+    uncertainty of inheritance in balsams and roses, ii. 18;
+    experiments with dwarf varieties of _Saponaria calabrica_ and _Tagetes
+        signata_, ii. 20;
+    reversion of flowers by stripes and blotches, ii. 37;
+    on variability, ii. 262.
+  _Vinca minor_, sterility in, ii. 170.
+  VINE, i. 332-334;
+    parsley-leaved, reversion of, i. 382;
+    graft-hybrid produced by inosculation in the, i. 395;
+    disease of, influenced by colour of grapes, ii. 228;
+    influence of climate, &c., on varieties of the, ii. 278;
+    diminished extent of cultivation of the, ii. 308;
+    acclimatisation of the, in the West Indies, ii. 313.
+  _Viola_, species of, i. 368.
+  _Viola lutea_, different coloured flowers in, i. 408.
+  _Viola tricolor_, reversion in, ii. 31, 47.
+  VIRCHOW, Prof., blindness occurring in the offspring of consanguineous
+      marriages, ii. 143;
+    on the growth of bones, ii. 294, 381;
+    on cellular prolification, ii. 295;
+    independence of the elements of the body, ii. 369;
+    on the cell-theory, ii. 370;
+    presence of hairs and teeth in ovarian tumours, ii. 370;
+    of hairs in the brain, ii. 391;
+    special affinities of the tissues, ii. 380;
+    origin of polypoid excrescences and tumours, ii. 381.
+  VIRGIL on the selection of seed-corn, i. 318, ii. 203;
+    of cattle and sheep, ii. 202.
+  VIRGINIAN islands, ponies of, i. 52.
+  _Virgularia_, ii. 378.
+  VISION, hereditary peculiarities of, ii. 8-9;
+  {484}
+    in amphibious animals, ii. 223;
+    varieties of, ii. 300;
+    affections of organs of, correlated with other peculiarities, ii. 328.
+  _Vitis vinifera_, i. 332-334, 375.
+  _Viverra_, sterility of species of, in captivity, ii. 151.
+  VOGEL, varieties of the date palm, ii. 256.
+  VOGT, on the indications of stripes on black kittens, ii. 55.
+  VOICE, differences of, in fowls, i. 259;
+    peculiarities of, in ducks, i. 281;
+    inheritance of peculiarities of, ii. 6.
+  VOLZ, on the history of the dog, i. 16;
+    ancient history of the fowl, i. 246;
+    domestic ducks unknown to Aristotle, i. 277;
+    Indian cattle sent to Macedonia by Alexander, ii. 202;
+    mention of mules in the Bible, ii. 202;
+    history of the increase of breeds, ii. 244.
+  VON BERG on _Verbascum phoeniceum_, ii. 305.
+  VOORHELM, G., his knowledge of hyacinths, i. 371, ii. 251.
+  VROLIK, Prof., on polydactylism, ii. 12;
+    on double monsters, ii. 340;
+    influence of the shape of the mother's pelvis on her child's head, ii.
+        344.
+
+  WADERS, behaviour of, in confinement, ii. 156.
+  WAHLENBERG, on the propagation of Alpine plants by buds, runners, bulbs,
+      &c., ii. 169.
+  "WAHLVERWANDTSCHAFT" of Gaertner, ii. 180.
+  WALES, white cattle of, in the 10th century, i. 85.
+  WALKER, A., on intermarriage, i. 404;
+    on the inheritance of polydactylism, ii. 13.
+  WALKER, D., advantage of change of soil to wheat, ii. 146.
+  WALLACE, A. R., on a striped Javanese horse, i. 59;
+    on the conditions of life of feral animals, ii. 32;
+    artificial alteration of the plumage of birds, ii. 280;
+    on polymorphic butterflies, ii. 399-400;
+    on reversion, ii. 415;
+    on the limit of change, ii. 417.
+  WALLACE, Dr., on the sterility of Sphingidae hatched in autumn, ii. 158.
+  WALLACHIAN sheep, sexual peculiarities in the horns of, i. 96.
+  WALLFLOWER, bud-variation in, i. 382.
+  WALLICH, Dr., on _Thuja pendula_ or _filiformis_, i. 362.
+  WALNUTS, i. 356-357;
+    thin-shelled, attacked by tomtits, ii. 231;
+    grafting of, ii. 259.
+  WALSH, B. D., on galls, ii. 282, 283;
+    his "Law of equable variability," ii. 351-352.
+  WALTHER, F. L., on the history of the dog, i. 16;
+    on the intercrossing of the zebu and ordinary cattle, i. 83.
+  WARING, Mr., on individual sterility, ii. 162.
+  WART hog, i. 76.
+  WATERER, Mr., spontaneous production of _Cytisus alpino-laburnum_, i.
+      390.
+  WATER melon, i. 357.
+  WATERHOUSE, G. R., on the winter-colouring of _Lepus variabilis_, i. 111.
+  WATERTON, C., production of tailless foals, i. 53;
+    on taming wild ducks, i. 278;
+    on the wildness of half-bred wild ducks, ii. 45;
+    assumption of male characters by a hen, ii. 51.
+  WATSON, H. C., on British wild fruit-trees, i. 312;
+    on the non-variation of weeds, i. 317;
+    origin of the plum, i. 345;
+    variation in _Pyrus malus_, i. 348;
+    on _Viola amoena_ and _tricolor_, i. 368;
+    on reversion in Scotch kail, ii. 32;
+    fertility of _Draba sylvestris_ when cultivated, ii. 163;
+    on generally distributed British plants, ii. 285.
+  WATTLES, rudimentary, in some fowls, ii. 315.
+  WATTS, Miss, on Sultan fowls, i. 228.
+  WEBB, James, interbreeding of sheep, ii. 120.
+  WEBER, effect of the shape of the mother's pelvis on her child's head,
+      ii. 344.
+  WEEDS, supposed necessity for their modification, coincidently with
+      cultivated plants, i. 317.
+  WEEPING varieties of trees, i. 361.
+  WEEPING habit of trees, capricious inheritance of, ii. 18-19.
+  WEEVIL, injury done to stone-fruit by, in North America, ii. 231.
+  WELSH cattle, descended from _Bos longifrons_, i. 81.
+  WEST Indies, feral pigs of, i. 77;
+    effect of climate of, upon sheep, i. 98.
+  WESTERN, Lord, change effected by, in the sheep, ii. 198.
+  WESTPHALIA, striped young pigs in, i. 76.
+  WESTWOOD, J. O., on peloric flowers of _Calceolaria_, ii. 346.
+  WHATELY, Archbishop, on grafting early and late thorns, i. 363.
+  WHEAT, specific unity or diversity of, i. 312-313, 316-317;
+    Hasora, i. 313;
+    presence or absence of barbs in, i. 314;
+    Godron on variations in, _ibid._;
+    varieties of, i. 314-315;
+    effects of soil and climate on, i. 316;
+    deterioration of, _ibid._;
+    crossing of varieties of, _ibid._, ii. 96, 104-105, 130;
+    in the Swiss lake-dwellings, i. 317-319;
+    selection applied to, i. 318, ii. 200;
+    increased fertility of hybrids of, with _Aegilops_, ii. 110;
+    advantage of change of soil to, ii. 146;
+  {485}
+    differences of, in various parts of India, ii. 165;
+    continuous variation in, ii. 200;
+    red, hardiness of, ii. 229, 336;
+    Fenton, ii. 232;
+    natural selection in, ii. 233;
+    varieties of, found wild, ii. 260;
+    effects of change of climate on, ii. 307;
+    ancient variety of, ii. 429.
+  WHITBY, Mrs., on the markings of silkworms, i. 302;
+    on the silkmoth, i. 303.
+  WHITE, Mr., reproduction of supernumerary digits after amputation, ii.
+      14;
+    time occupied in the blending of crossed races, ii. 87.
+  WHITE, Gilbert, vegetable diet of dogs, ii. 303.
+  WHITE and white-spotted animals, liability of, to disease, ii. 336-337.
+  WHITE flowers, most truly reproduced by seed, ii. 20.
+  WICHURA, Max, on hybrid willows, ii. 50, 131, 267;
+    analogy between the pollen of old-cultivated plants, and of hybrids,
+        ii. 268.
+  WICKING, Mr., inheritance of the primary characters of _Columba livia_ in
+      cross-bred pigeons, i. 201;
+    production of a white head in almond tumblers, ii. 199.
+  WICKSTED, Mr., on cases of individual sterility, ii. 162.
+  WIEGMANN, spontaneous crossing of blue and white peas, i. 397;
+    crossing of varieties of cabbage, ii. 130;
+    on contabescence, ii. 165.
+  WIGHT, Dr., sexual sterility of plants propagated by buds, &c., ii. 169.
+  WILDE, Sir W. R., occurrence of _Bos frontosus_ and _longifrons_ in Irish
+      crannoges, i. 81;
+    attention paid to breeds of animals by the ancient Irish, ii. 203.
+  WILDMAN, on the dahlia, ii. 216, 273.
+  WILDNESS of the progeny of crossed tame animals, ii. 44-46.
+  WILKES, Capt., on the taming of pigeons among the Polynesians, ii. 161.
+  WILKINSON, J., on crossed cattle, ii. 104.
+  WILLIAMS, Mr., change of plumage in a Hamburgh hen, i. 258.
+  WILLIAMS, Mr., intercrossing of strawberries, i. 352.
+  WILLIAMSON, Capt., degeneration of dogs in India, i. 37;
+    on small Indian asses, i. 62.
+  WILLIAMSON, Rev. W., doubling of _Anemone coronaria_ by selection, ii.
+      200.
+  WILLOWS, weeping, i. 361;
+    reversion of spiral-leaved weeping, i. 383;
+    hybrids of, ii. 267;
+    galls of, ii. 282-283.
+  WILLOUGHBY, F., notice of spot pigeons, i. 156;
+    on a fantail pigeon, i. 208;
+    on tumbler pigeons, i. 209;
+    on the turbit, i. 209;
+    on the barb and carrier pigeons, i. 211;
+    on the hook-billed duck, i. 277.
+  WILMOT, Mr., on a crested white Turkey cock, i. 293;
+    reversion of sheep in colour, ii. 30.
+  WILSON, B. O., fertility of hybrids of humped and ordinary cattle in
+      Tasmania, i. 83.
+  WILSON, Dr., prepotency of the Manx over the common cat, ii. 66.
+  WILSON, James, origin of dogs, i. 16.
+  WILSON, Mr., on prepotency of transmission in sheep, ii. 69;
+    on the breeding of bulls, ii. 196.
+  WINGS, proportionate length of, in different breeds of pigeons, i.
+      175-176;
+    of fowls, effects of disuse on, i. 270-272;
+    characters and variations of, in ducks, i. 284-286;
+    diminution of, in birds of small islands, i. 286-287.
+  WING-FEATHERS, number of, in pigeons, i. 159;
+    variability of, in fowls, i. 258.
+  WOLF, recent existence of, in Ireland, i. 16;
+    barking of young, i. 27;
+    hybrids of, with the dog, i. 32.
+  WOLF-DOG, black, of Florida, i. 22.
+  WOLVES, North American, their resemblance to dogs of the same region, i.
+      21-22;
+    burrowing of, i. 27.
+  WOODBURY, Mr., crossing of the Ligurian and common hive bees, i. 299, ii.
+      126;
+    variability of bees, i. 298.
+  WOODWARD, S. P., on Arctic Mollusca, ii. 256.
+  WOOD, Willoughby, on Mr. Bates' cattle, ii. 118.
+  WOOLER, W. A., on the young of the Himalayan rabbit, i. 109;
+    persistency of the coloured calyx in a crossed Polyanthus, i. 365.
+  WORRARA poison, ii. 380.
+  WOUNDS, healing of, ii. 294.
+  WRIGHT, J., production of crippled calves by shorthorned cattle, ii. 118;
+    on selection in cattle, ii. 194;
+    effect of close interbreeding on pigs, ii. 121-122;
+    deterioration of game cocks by close interbreeding, ii. 124.
+  WRIGHT, Strethill, on the development of the hydroida, ii. 368.
+  WYMAN, Dr., on Niata cattle, and on a similar malformation in the
+      codfish, i. 89;
+    on Virginian pigs, ii. 227.
+
+  XENOPHON, on the colours of hunting dogs, ii. 209.
+  XIMENES, Cardinal, regulations for the selection of rams, ii. 204.
+
+  "YAHOO," the name of the pigeon in Persia, i. 155.
+  YAKS, domestication of, i. 82;
+    selection of white-tailed, ii. 206, 209.
+  {486}
+  YAM, development of axillary bulbs in the, ii. 169.
+  YARRELL, Mr., deficiency of teeth in hairless dogs, i. 34, ii. 326;
+    on ducks, i. 279, ii. 262;
+    characters of domestic goose, resembling those of _Anser albifrons_, i.
+        288;
+    whiteness of ganders, i. 288;
+    variations in goldfish, i. 296-297;
+    assumption of male plumage by the hen-pheasant, ii. 51;
+    effect of castration upon the cock, ii. 51-52;
+    breeding of the skylark in captivity, ii. 154;
+    plumage of the male linnet in confinement, ii. 158;
+    on the dingo, ii. 263.
+  YELLOW fever, in Mexico, ii. 276.
+  YEW, fastigate, ii. 241.
+  YEW, Irish, hardy in New York, ii. 309.
+  YEW, weeping, i. 361;
+    propagation of, by seed, ii. 18-19.
+  YOLK, variations of, in the eggs of ducks, i. 281.
+  YOUATT, Mr., history of the dog, i. 16-17;
+    variations of the pulse in breeds of dogs, i. 35;
+    liability to disease in dogs, i. 35, ii. 227;
+    inheritance of goitre in dogs, ii. 10;
+    on the greyhound, i. 34, 41;
+    on King Charles' spaniels, i. 41;
+    on the setter, i. 41;
+    on breeds of horses, i. 49;
+    variation in the number of ribs in the horse, i. 50;
+    inheritance of diseases in the horse, ii. 10, 11;
+    introduction of Eastern blood into English horses, ii. 212-213;
+    on white Welsh cattle, i. 85, ii. 209;
+    improvement of British breeds of cattle, i. 93;
+    rudiments of horns in young hornless cattle, ii. 55, 315;
+    on crossed cattle, ii. 104, 119;
+    on Bakewell's long-horned cattle, ii. 118;
+    selection of qualities in cattle, ii. 196;
+    degeneration of cattle by neglect, ii. 239;
+    on the skull in hornless cattle, ii. 333;
+    disease of white parts of cattle, ii. 337;
+    displacement of long-horned by short-horned cattle, ii. 426;
+    on Angola sheep, i. 95;
+    on the fleece of sheep, i. 99;
+    correlation of horns and fleece in sheep, i. 95;
+    adaptation of breeds of sheep to climate and pasture, i. 96;
+    horns of Wallachian sheep, i. 96;
+    exotic sheep in the Zoological Gardens, i. 96-97, ii. 305;
+    occurrence of horns in hornless breeds of sheep, ii. 30;
+    on the colour of sheep, ii. 30;
+    on interbreeding sheep, ii. 120;
+    on Merino rams in Germany, ii. 196;
+    effect of unconscious selection on sheep, ii. 213;
+    reversion of Leicester sheep on the Lammermuir Hills, ii. 224;
+    on many-horned sheep, ii. 326;
+    reduction of bone in sheep, ii. 242;
+    persistency of character in breeds of animals in mountainous countries,
+        ii. 64;
+    on interbreeding, ii. 116;
+    on the power of selection, ii. 194-195;
+    slowness of production of breeds, ii. 244;
+    passages in the Bible relating to the breeding of animals, ii. 201-202.
+  YOUNG, J., on the Belgian rabbit, i. 106.
+  YULE, Capt., on a Burmese hairy family, ii. 77, 327.
+
+  ZAMBESI, striped young pigs on the, i. 77.
+  ZAMBOS, character of the, ii. 47.
+  ZANO, J. G., introduction of rabbits into Porto Santo by, i. 112.
+  _Zea Mays_, i. 320.
+  ZEBU, i. 79;
+    domestication of the, i. 82;
+    fertile crossing of, with European cattle, i. 83, ii. 110.
+  ZEBRA, hybrids of, with the ass and mare, ii. 42.
+  _Zephyranthes candida_, ii. 164.
+  _Zinnia_, cultivation of, ii. 261.
+  ZOLLINGER on Malayan penguin ducks, i. 280.
+  ZOOSPORE, division of, in Algae, ii. 378.
+  "ZOPF-TAUBE," i. 154.
+
+THE END.
+
+LONDON: PRINTED BY W. CLOWES AND SONS, DUKE STREET, STAMFORD STREET, AND
+CHARING CROSS.
+
+       *       *       *       *       *
+
+
+NOTES
+
+[1] 'Medical Notes and Reflections,' 3rd edit., 1855, p. 267.
+
+[2] Mr. Buckle, in his grand work on 'Civilisation,' expresses doubts on
+the subject owing to the want of statistics. _See_ also Mr. Bowen,
+Professor of Moral Philosophy, in 'Proc. American Acad. of Sciences,' vol.
+v. p. 102
+
+[3] For greyhounds, _see_ Low's 'Domest. Animals of the British Islands,'
+1845, p. 721. For game-fowls, _see_ 'The Poultry Book,' by Mr. Tegetmeier,
+1866, p. 123. For pigs, _see_ Mr. Sidney's edit. of 'Youatt on the Pig,'
+1860, pp. 11, 22.
+
+[4] 'The Stud Farm,' by Cecil, p. 39.
+
+[5] 'Philosophical Transactions,' 1755, p. 23. I have seen only second-hand
+accounts of the two grandsons. Mr. Sedgwick, in a paper to which I shall
+hereafter often refer, states that _four_ generations were affected, and in
+each the males alone.
+
+[6] Barbara Van Beck, figured, as I am informed by the Rev. W. D. Fox, in
+Woodburn's 'Gallery of Rare Portraits,' 1816, vol. ii.
+
+[7] 'Proc. Zoolog. Soc.,' 1833, p. 16
+
+[8] Hofacker, 'Ueber die Eigenschaften,' &c., 1828, s. 34. Report by
+Pariset in 'Comptes Rendus,' 1847, p. 592.
+
+[9] Hunter, as quoted in Harlan's 'Med. Researches,' p. 530. Sir A.
+Carlisle, 'Phil. Transact.,' 1814, p. 94.
+
+[10] Girou de Buzareignues, 'De la Generation,' p. 282.
+
+[11] 'Macmillan's Magazine,' July and August, 1865.
+
+[12] The works which I have read and found most useful are Dr. Prosper
+Lucas's great work, 'Traite de l'Heredite Naturelle,' 1847. Mr. W.
+Sedgwick, in 'British and Foreign Medico-Chirurg. Review,' April and July,
+1861, and April and July, 1863: Dr. Garrod on Gout is quoted in these
+articles. Sir Henry Holland, 'Medical Notes and Reflections,' 3rd edit.,
+1855. Piorry, 'De l'Heredite dans les Maladies,' 1840. Adams, 'A
+Philosophical Treatise on Hereditary Peculiarities,' 2nd edit., 1815. Essay
+on 'Hereditary Diseases,' by Dr. J. Steinan, 1843. _See_ Paget, in 'Medical
+Times,' 1857, p. 192, on the Inheritance of Cancer; Dr. Gould, in 'Proc. of
+American Acad. of Sciences,' Nov. 8, 1853, gives a curious case of
+hereditary bleeding in four generations. Harlan, 'Medical Researches,' p.
+593.
+
+[13] Marshall, quoted by Youatt in his work on Cattle, p. 284.
+
+[14] 'Philosoph. Transact.,' 1814, p. 94.
+
+[15] 'Medical Notes and Reflections,' 3rd edit., p. 33.
+
+[16] This affection, as I hear from Mr. Bowman, has been ably described and
+spoken of as hereditary by Dr. Dondera, of Utrecht, whose work was
+published in English by the Sydenham Society in 1864.
+
+[17] Quoted by Mr. Herbert Spencer, 'Principles of Biology,' vol. i. p.
+244.
+
+[18] 'British and Foreign Medico-Chirurg. Review, 'April, 1861, p. 482-6;
+'l'Hered. Nat.,' tom. i. pp. 391-408.
+
+[19] Dr. Osborne, Pres. of Royal College of Phys. in Ireland, published
+this case in the 'Dublin Medical Journal' for 1835.
+
+[20] These various statements are taken from the following works and
+papers:--Youatt on 'The Horse,' pp. 35, 220. Lawrence, 'The Horse,' p. 30.
+Karkeek, in an excellent paper in 'Gard. Chronicle,' 1853, p. 92. Mr.
+Burke, in 'Journal of R. Agricul. Soc. of England,' vol. v. p. 511.
+'Encyclop. of Rural Sports,' p. 279. Girou de Buzareignues, 'Philosoph.
+Phys.,' p. 215. _See_ following papers in 'The Veterinary:' Roberts, in
+vol. ii. p. 144; M. Marrimpoey, vol. ii. p. 387; Mr. Karkeek, vol. iv. p.
+5; Youatt on Goitre in Dogs, vol. v. p. 483; Youatt, in vol. vi. pp. 66,
+348, 412; M. Bernard, vol. xi. p. 539; Dr. Samesreuther, on Cattle, in vol.
+xii. p. 181; Percivall, in vol. xiii. p. 47. With respect to blindness in
+horses, _see_ also a whole row of authorities in Dr. P. Lucas's great work,
+tom. i. p. 399. Mr. Baker, in 'The Veterinary,' vol. xiii. p. 721, gives a
+strong case of hereditary imperfect vision and of jibbing.
+
+[21] Knight on 'The Culture of the Apple and Pear,' p. 31. Lindley's
+'Horticulture,' p. 180.
+
+[22] These statements are taken from the following works in order:--Youatt
+on 'The Horse,' p. 48; Mr. Darvill, in 'The Veterinary,' vol. viii. p. 50.
+With respect to Robson, _see_ 'The Veterinary,' vol. iii. p. 580; Mr.
+Lawrence on 'The Horse,' 1829, p. 9; 'The Stud Farm,' by Cecil, 1851; Baron
+Cameronn, quoted in 'The Veterinary,' vol x. p. 500.
+
+[23] 'Recreations in Agriculture and Nat. Hist.,' vol. i. p. 68.
+
+[24] 'Ueber die Eigenschaften,' &c., 1828, s. 107.
+
+[25] Bronn's 'Geschichte der Natur,' band ii. s. 132.
+
+[26] Vrolik has discussed this point at full length in a work published in
+Dutch, from which Mr. Paget has kindly translated for me passages. _See_,
+also, Isidore Geoffroy St. Hilaire's 'Hist. des Anomalies,' 1832, tom. i.
+p. 684.
+
+[27] 'Edinburgh New Phil. Journal,' July, 1863.
+
+[28] Some great anatomists, as Cuvier and Meckel, believe that the tubercle
+one side of the hinder foot of the tailless Batrachians represents a sixth
+digit. Certainly, when the hinder foot of a toad, as soon as it first
+sprouts from the tadpole, is dissected, the partially ossified cartilage of
+this tubercle resembles under the microscope, in a remarkable manner, a
+digit. But the highest authority on such subjects, Gegenbaur (Untersuchung.
+zur vergleich. anat. der Wirbelthiere: Carpus et Tarsus, 1864, s. 63),
+concludes that this resemblance is not real, only superficial.
+
+[29] For these several statements, _see_ Dr. Struthers, in work cited,
+especially on intermissions in the line of descent. Prof. Huxley, 'Lectures
+on our Knowledge of Organic Nature,' 1863, p. 97. With respect to
+inheritance, _see_ Dr. Prosper Lucas, 'L'Heredite Nat.,' tom. i. p. 325.
+Isid. Geoffroy, 'Anom.,' tom. i. p. 701. Sir A. Carlisle, in 'Phil.
+Transact.,' 1814, p. 94. A. Walker, on 'Intermarriage,' 1838, p. 140, gives
+a case of five generations; as does Mr. Sedgwick, in 'Brit. and Foreign
+Medico-Chirurg. Review,' April, 1863, p. 462. On the inheritance of other
+anomalies in the extremities, _see_ Dr. H. Dobell, in vol. xlvi. of
+'Medico-Chirurg. Transactions,' 1863; also Mr. Sedgwick, in op. cit.,
+April, 1863, p. 460. With respect to additional digits in the negro, _see_
+Prichard, 'Physical History of Mankind.' Dr. Dieffenbach ('Journ. Royal
+Geograph. Soc.,' 1841, p. 208) says this anomaly is not uncommon with the
+Polynesians of the Chatham Islands.
+
+[30] 'The Poultry Chronicle,' 1854, p. 559.
+
+[31] The statements in this paragraph are taken from Isidore Geoffroy St.
+Hilaire, 'Hist. des Anomalies,' tom. i. pp. 688-693.
+
+[32] As quoted by Carpenter, 'Princ. of Comp. Physiology,' 1854, p. 480.
+
+[33] Mueller's 'Phys.,' Eng. translat., vol. i. 1838, p. 407. A thrush,
+however, was exhibited before the British Association at Hull, in 1853,
+which had lost its tarsus, and this member, it was asserted, had been
+thrice reproduced: I presume it was lost each time by disease.
+
+[34] 'Monthly Journal of Medical Science,' Edinburgh, 1848, new series,
+vol. ii. p. 890.
+
+[35] 'An Essay on Animal Reproduction,' trans. by Dr. Maty, 1769, p. 79.
+
+[36] Bonnet, 'Oeuvres d'Hist. Nat.,' tom. v., part i., 4to. edit., 1781,
+pp. 343, 350, 353.
+
+[37] So with insects, the larvae reproduce lost limbs, but, except in one
+order, the mature insect has no such power. But the Myriapoda, which
+apparently represent the larvae of true insects, have, as Newport has
+shown, this power until their last moult. _See_ an excellent discussion on
+this whole subject by Dr. Carpenter in his 'Princ. Comp. Phys.,' 1854, p.
+479.
+
+[38] Dr. Guenther, in Owen's 'Anatomy of Vertebrates,' vol. i., 1866, p.
+567. Spallanzani has made similar observations.
+
+[39] 'On the Anatomy of Vertebrates,' 1866, p. 170: with respect to the
+pectoral fins of fishes, pp. 166-168.
+
+[40] 'Medical Notes and Reflections,' 1839, pp. 24, 34. _See_, also, Dr. P.
+Lucas, 'l'Hered. Nat.,' tom. ii. p. 33.
+
+[41] 'Du Danger des Mariages Consanguins,' 2nd edit., 1862, p. 103.
+
+[42] 'British and Foreign Medico-Chirurg. Review,' July, 1863, pp. 183,
+189.
+
+[43] Verlot, 'La Production des Varietes,' 1865, p. 32.
+
+[44] Loudon's 'Gard. Mag.,' vol. xii., 1836, p. 368.
+
+[45] Verlot, 'La Product. des Varietes,' 1865, p. 94.
+
+[46] Bronn's 'Geschichte der Natur,' b. ii. s. 121.
+
+[47] Rev. W. A. Leighton, 'Flora of Shropshire,' p. 497; and Charlesworth's
+'Mag. of Nat. Hist.,' vol. i, 1837, p. 30.
+
+[48] Verlot, op. cit., p. 93.
+
+[49] For these several statements, _see_ Loudon's 'Gard. Magazine,' vol.
+x., 1834, pp. 408, 180; and vol. ix., 1833, p. 597.
+
+[50] These statements are taken from Alph. De Candolle, 'Bot. Geograph.,'
+p. 1083.
+
+[51] Verlot, op. cit., p. 38.
+
+[52] Op. cit., p. 59.
+
+[53] Alph. De Candolle, 'Geograph. Bot.,' p. 1082.
+
+[54] _See_ 'Cottage Gardener,' April 10, 1860, p. 18, and Sept. 10, 1861,
+p. 456; 'Gard. Chron.,' 1845, p. 102.
+
+[55] Darwin, in 'Journal of Proc. Linn. Soc. Bot.,' 1862, p. 94.
+
+[56] Hofacker, 'Ueber die Eigenschaften,' &c., s. 10.
+
+[57] Bechstein, 'Naturgesch. Deutschlands,' b. iv. s. 462. Mr. Brent, a
+great breeder of canaries, informs me that he believes that these
+statements are correct.
+
+[58] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 245.
+
+[59] 'British and Foreign Med.-Chirurg. Review,' July, 1861, pp. 200-204.
+Mr. Sedgwick has given such full details on this subject, with ample
+references, that I need refer to no other authorities.
+
+[60] 'De l'Espece,' tom. ii., 1859, p. 299.
+
+[61] 'Philosoph. Magazine,' vol. iv., 1799, p. 5.
+
+[62] This last case is quoted by Mr. Sedgwick in 'British and Foreign
+Medico-Chirurg. Review,' April, 1861, p. 484. For Blumenbach, _see_
+above-cited paper. _See_, also, Dr. P. Lucas, 'Traite de l'Hered. Nat.,'
+tom. ii. p. 492. Also 'Transact. Lin. Soc.,' vol. ix. p. 323. Some curious
+cases are given by Mr. Baker in 'The Veterinary,' vol. xiii. p. 723.
+Another curious case is given in the 'Annales des Scienc. Nat.,' 1st
+series, tom. xi. p. 324.
+
+[63] 'Proc. Royal Soc.,' vol. x. p. 297.
+
+[64] Mr. Sproule, in 'British Medical Journal,' April 18, 1863.
+
+[65] Downing, 'Fruits of America,' p. 5; Sageret, 'Pom. Phys.,' pp. 43, 72.
+
+[66] Youatt on Sheep, pp. 20, 234. The same fact of loose horns
+occasionally appearing in hornless breeds has been observed in Germany:
+Bechstein, 'Naturgesch. Deutschlands,' b. i. s. 362.
+
+[67] Youatt on Cattle, pp. 155, 174.
+
+[68] Youatt on Sheep, 1838, pp. 17, 145.
+
+[69] I have been informed of this fact through the Rev. W. D. Fox, on the
+excellent authority of Mr. Wilmot: _see_, also, remarks on this subject in
+an original article in the 'Quarterly Review,' 1849, p. 395.
+
+[70] Youatt, pp. 19, 234.
+
+[71] 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 231.
+
+[72] Loudon's 'Gard. Mag.,' vol. x., 1834, p. 396: a nurseryman, with much
+experience on this subject, has likewise assured me that this sometimes
+occurs.
+
+[73] 'Gardener's Chron.,' 1855, p. 777.
+
+[74] Ibid., 1862, p. 721.
+
+[75] _See_ some excellent remarks on this subject by Mr. Wallace, 'Journal
+Proc. Linn. Soc.,' 1858, vol. iii. p. 60.
+
+[76] Dureau de la Malle, in 'Comptes Rendus,' tom. xli., 1855, p. 807. From
+the statements above given, the author concludes that the wild pigs of
+Louisiana are not descended from the European _Sus scrofa_.
+
+[77] Capt. W. Allen, in his 'Expedition to the Niger,' states that fowls
+have run wild on the island of Annobon, and have become modified in form
+and voice. The account is so meagre and vague that it did not appear to me
+worth copying; but I now find that Dureau de la Malle ('Comptes Rendus,'
+tom. xli., 1855, p. 690) advances this as a good instance of reversion to
+the primitive stock, and as confirmatory of a still more vague statement in
+classical times by Varro.
+
+[78] 'Flora of Australia,' 1859, Introduct., p. ix.
+
+[79] 'De l'Espece,' tom. ii. pp. 54, 58, 60.
+
+[80] Mr. Sedgwick gives many instances in the 'British and Foreign
+Med.-Chirurg. Review,' April and July, 1863, pp. 448, 188.
+
+[81] In his edit. of 'Youatt on the Pig,' 1860, p. 27.
+
+[82] Dr. P. Lucas, 'Hered. Nat.,' tom. ii. pp. 314, 892: _see_ a good
+practical article on this subject in 'Gard. Chronicle,' 1856, p. 620. I
+could add a vast number of references, but they would be superfluous.
+
+[83] Koelreuter gives cases in his 'Dritte Fortsetzung,' 1766, s. 53, 59;
+and in his well-known 'Memoirs on Lavatera and Jalapa.' Gaertner,
+'Bastarderzeugung,' s. 437, 441, &c. Naudin, in his 'Recherches sur
+l'Hybridite, Nouvelles Archives du Museum,' tom. i. p. 25.
+
+[84] Quoted by Mr. Sedgwick in 'Med.-Chirurg. Review,' April, 1861, p. 485.
+Dr. H. Dobell, in 'Med.-Chirurg. Transactions,' vol. xlvi., gives an
+analogous case, in which, in a large family, fingers with thickened joints
+were transmitted to several members during five generations; but when the
+blemish once disappeared it never reappeared.
+
+[85] Verlot, 'Des Varietes,' 1865, p. 63.
+
+[86] 'Nouvelles Archives du Museum,' tom. i. p. 25. Alex. Braun (in his
+'Rejuvenescence,' Ray Soc., 1853, p. 315) apparently holds a similar
+opinion.
+
+[87] Mr. Teebay, in 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 72.
+
+[88] Quoted by Hofacker, 'Ueber die Eigenschaften,' &c., s. 98.
+
+[89] 'Essais Hist. Nat. du Paraguay,' tom. ii. 1801, p. 372.
+
+[90] These facts are given on the high authority of Mr. Hewitt, in 'The
+Poultry Book,' by Mr. Tegetmeier, 1866, p. 248.
+
+[91] 'The Poultry Book,' by Tegetmeier, 1866, p. 97.
+
+[92] 'Gardener's Chron. and Agricultural Gazette,' 1866, p. 528.
+
+[93] Ibid., 1860, p. 343.
+
+[94] Sclater, in 'Proc. Zoolog. Soc.,' 1862, p. 163.
+
+[95] 'History of the Horse,' p. 212.
+
+[96] 'Mem. presentes par divers Savans a l'Acad. Royale,' tom. vi. 1835, p.
+338.
+
+[97] 'Letters from Alabama,' 1859, p. 280.
+
+[98] 'Hist. Nat. des Mammiferes,' 1820, tom. i.
+
+[99] 'Philosoph. Transact.,' 1821, p. 20.
+
+[100] Sclater, in 'Proc. Zoolog. Soc.,' 1862, p. 163: this species is the
+Ghor-Khur of N.W. India, and has often been called the Hemionus of Pallas.
+_See_, also, Mr. Blyth's excellent paper in 'Journ. of Asiatic Soc. of
+Bengal,' vol. xxviii., 1860, p. 229.
+
+[101] Another species of wild ass, the true _A. hemionus_ or _Kiang_, which
+ordinarily has no shoulder-stripes, is said occasionally to have them; and
+these, as with the horse and ass, are sometimes double: _see_ Mr. Blyth, in
+the paper just quoted, and in 'Indian Sporting Review,' 1856, p. 320; and
+Col. Hamilton Smith, in 'Nat. Library, Horses,' p. 318; and 'Dict. Class.
+d'Hist. Nat.,' tom. iii. p. 563.
+
+[102] Figured in the 'Gleanings from the Knowsley Menageries,' by Dr. J. E.
+Gray.
+
+[103] Cases of both Spanish and Polish hens sitting are given in the
+'Poultry Chronicle,' 1855, vol. iii. p. 477.
+
+[104] 'The Poultry Book,' by Mr. Tegetmeier, 1866, pp. 119, 163. The
+author, who remarks on the two negatives ('Journ. of Hort.,' 1862, p. 325),
+states that two broods were raised from a Spanish cock and Silver-pencilled
+Hamburgh hen, neither of which are incubators, and no less than seven out
+of eight hens in these two broods "showed a perfect obstinacy in sitting."
+The Rev. E. S. Dixon ('Ornamental Poultry,' 1848, p. 200) says that
+chickens reared from a cross between Golden and Black Polish fowls, are
+"good and steady birds to sit." Mr. B. P. Brent informs me that he raised
+some good sitting hens by crossing Pencilled Hamburgh and Polish breeds. A
+cross-bred bird from a Spanish non-incubating cock and Cochin incubating
+hen is mentioned in the 'Poultry Chronicle,' vol. iii. p. 13, as an
+"exemplary mother." On the other hand, an exceptional case is given in the
+'Cottage Gardener,' 1860, p. 388, of a hen raised from a Spanish cock and
+black Polish hen which did not incubate.
+
+[105] 'The Poultry Book,' by Tegetmeier, 1866, pp. 165, 167.
+
+[106] 'Natural History Review,' 1863, April, p. 277.
+
+[107] 'Essays on Natural History,' p. 197.
+
+[108] As stated by Mr. Orton, in his 'Physiology of Breeding,' p. 12.
+
+[109] M. E. de Selys-Longchamps refers ('Bulletin Acad. Roy. de Bruxelles,'
+tom. xii. No. 10) to more than seven of these hybrids shot in Switzerland
+and France. M. Deby asserts ('Zoologist,' vol. v., 1845-46, p. 1254) that
+several have been shot in various parts of Belgium and Northern France.
+Audubon ('Ornitholog. Biography,' vol. iii. p. 168), speaking of these
+hybrids, says that, in North America, they "now and then wander off and
+become quite wild."
+
+[110] 'Journal of Researches,' 1845, p. 71.
+
+[111] 'Expedition to the Zambesi,' 1865, pp. 25, 150.
+
+[112] Dr. P. Broca, on 'Hybridity in the Genus Homo,' Eng. translat., 1864,
+p. 39.
+
+[113] 'Nouvelles Archives du Museum,' tom. i. p. 151.
+
+[114] 'Bastarderzeugung,' s. 582, 438, &c.
+
+[115] 'Die Bastardbefruchtung ... der Weiden,' 1865, s. 23. For Gaertner's
+remarks on this head, _see_ 'Bastarderzeugung,' s. 474, 582.
+
+[116] Yarrell, 'Phil. Transact.,' 1827, p. 268; Dr. Hamilton, in 'Proc.
+Zoolog. Soc.,' 1862, p. 23.
+
+[117] 'Archiv. Skand. Beitraege zur Naturgesch.,' viii. s. 397-413.
+
+[118] In his 'Essays on Nat. Hist.,' 1838. Mr. Hewitt gives analogous cases
+with hen-pheasants in 'Journal of Horticulture,' July 12, 1864, p. 37.
+Isidore Geoffroy Saint Hilaire, in his 'Essais de Zoolog. Gen.' (suites a
+Buffon, 1842, pp. 496-513), has collected such cases in ten different kinds
+of birds. It appears that Aristotle was well aware of the change in mental
+disposition in old hens. The case of the female deer acquiring horns is
+given at p. 513.
+
+[119] 'Cottage Gardener,' 1860, p. 379.
+
+[120] 'Art de faire Eclorre,' &c., 1749, tom. ii. p. 8.
+
+[121] Sir H. Holland, 'Medical Notes and Reflections,' 3rd edit., 1855, p.
+31.
+
+[122] Prof. Thomson on Steenstrup's Views on the Obliquity of Flounders:
+'Annals and Mag. of Nat. Hist.,' May, 1865, p. 361.
+
+[123] Dr. E. von Martens, in 'Annals and Mag. of Nat. Hist.,' March, 1866,
+p. 209.
+
+[124] Darwin, 'Balanidae,' Ray Soc., 1854, p. 499: _see_ also the appended
+remarks on the apparently capricious development of the thoracic limbs on
+the right and left sides in the higher crustaceans.
+
+[125] Mormodes ignea: Darwin, 'Fertilization of Orchids,' 1862, p. 251.
+
+[126] 'Journal of Horticulture,' July, 1864, p. 38. I have had the
+opportunity of examining these remarkable feathers through the kindness of
+Mr. Tegetmeier.
+
+[127] 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 241.
+
+[128] Carl Vogt, 'Lectures on Man,' Eng. translat., 1864, p. 411.
+
+[129] On Cattle, p. 174.
+
+[130] Isid. Geoffroy St. Hilaire, 'Des Anomalies,' tom. iii. p. 353. With
+respect to the mammae in women, _see_ tom. i. p. 710.
+
+[131] 'Natural Hist. Review,' April, 1863, p. 258. _See_ also his Lecture,
+Royal Institution, March 16, 1860. On same subject, _see_ Moquin-Tandon,
+'Elements de Teratologie,' 1841, pp. 184, 352.
+
+[132] Verlot, 'Des Varietes,' 1865, p. 89; Naudin, 'Nouvelles Archives du
+Museum,' tom. i. p. 137.
+
+[133] In his discussion on some curious peloric calceolarias, quoted in
+'Journal of Horticulture,' Feb. 24, 1863, p. 152.
+
+[134] For other cases of six divisions in peloric flowers of the Labiatae
+and Scrophulariaceae, _see_ Moquin-Tandon, 'Teratologie,' p. 192.
+
+[135] Moquin-Tandon, 'Teratologie,' p. 186.
+
+[136] _See_ Youatt on Cattle, pp. 92, 69, 78, 88, 163: also Youatt on
+Sheep, p. 325. Also Dr. Lucas, 'L'Hered. Nat.,' tom. ii. p. 310.
+
+[137] 'Hered. Nat.,' tom. ii. pp. 112-120.
+
+[138] Sir H. Holland, 'Chapters on Mental Physiology,' 1852, p. 234.
+
+[139] 'Gardener's Chronicle,' 1860, p. 270.
+
+[140] Mr. N. H. Smith, Observations on Breeding, quoted in 'Encyclop. of
+Rural Sports,' p. 278.
+
+[141] Quoted by Bronn, 'Geschichte der Natur,' b. ii. s. 170. _See_ Sturm,
+'Ueber Racen,' 1825, s. 104-107. For the niata cattle, _see_ my 'Journal of
+Researches,' 1845, p. 146.
+
+[142] Lucas, 'l'Heredite Nat.,' tom. ii. p. 112.
+
+[143] Mr. Orton, 'Physiology of Breeding,' 1855, p. 9.
+
+[144] Boitard and Corbie, 'Les Pigeons,' 1824, p. 224.
+
+[145] 'Les Pigeons, pp. 168, 198.
+
+[146] 'Das Ganze,' &c., 1837, s. 39.
+
+[147] 'The Pigeon Book,' p. 46.
+
+[148] 'Physiology of Breeding,' p.22; Mr. Hewitt, in 'The Poultry Book,' by
+Tegetmeier, 1866, p. 224.
+
+[149] Boitard and Corbie, 'Les Pigeons,' 1824, p. 226.
+
+[150] 'Bastarderzeugung,' s. 256, 290, &c. Naudin ('Nouvelles Archives du
+Museum,' tom. i. p. 149) gives a striking instance of prepotency in _Datura
+stramonium_ when crossed with two other species.
+
+[151] Flourens, 'Longevite Humaine,' p. 144, on crossed jackals. With
+respect to the difference between the mule and the hinny, I am aware that
+this has generally been attributed to the sire and dam transmitting their
+characters differently; but Colin, who has given in his 'Traite Phys.
+Comp.,' tom. ii. pp. 537-539, the fullest description which I have met with
+of these reciprocal hybrids, is strongly of opinion that the ass
+preponderates in both crosses, but in an unequal degree. This is likewise
+the conclusion of Flourens, and of Bechstein in his 'Naturgeschichte
+Deutschlands,' b. i. s. 294. The tail of the hinny is much more like that
+of the horse than is the tail of the mule, and this is generally accounted
+for by the males of both species transmitting with greater power this part
+of their structure; but a compound hybrid which I saw in the Zoological
+Gardens, from a mare by a hybrid ass-zebra, closely resembled its mother in
+its tail.
+
+[152] Mr. Hewitt, who has had such great experience in raising these
+hybrids, says ('Poultry Book,' by Mr. Tegetmeier, 1866, pp. 165-167) that
+in all, the head was destitute of wattles, comb, and ear-lappets; and all
+closely resembled the pheasant in the shape of the tail and general contour
+of the body. These hybrids were raised from hens of several breeds by a
+cock-pheasant; but another hybrid, described by Mr. Hewitt, was raised from
+a hen-pheasant by a silver-laced Bantam cock, and this possessed a
+rudimental comb and wattles.
+
+[153] 'L'Hered. Nat.,' tom. ii. book ii. ch. i.
+
+[154] 'Bastarderzeugung,' s. 264-266. Naudin ('Nouvelles Archives du
+Museum,' tom. i. p. 148) has arrived at a similar conclusion.
+
+[155] 'Cottage Gardener,' 1856, pp. 101, 137.
+
+[156] _See_ some remarks on this head with respect to sheep by Mr. Wilson,
+in 'Gardener's Chronicle,' 1863, p. 15.
+
+[157] Verlot, 'Des Varietes,' 1865, p. 66.
+
+[158] Moquin-Tandon, 'Teratologie,' p. 191.
+
+[159] 'Nouvelles Archives du Museum,' tom. i. p. 137.
+
+[160] 'L'Hered. Nat.,' tom. ii. pp. 137-165. _See_, also, Mr. Sedgwick's
+four memoirs, immediately to be referred to.
+
+[161] On Sexual Limitation in Hereditary Diseases, 'Brit. and For.
+Med.-Chirurg. Review,' April, 1861, p. 477; July, p. 198; April, 1863, p.
+44; and July, p. 159.
+
+[162] W. Scrope, 'Art of Deer Stalking,' p. 354.
+
+[163] Boitard and Corbie, 'Les Pigeons,' p. 173; Dr. F. Chapuis, 'Le Pigeon
+Voyageur Belge,' 1865, p. 87.
+
+[164] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 349.
+
+[165] 'Embassy to the Court of Ava,' vol. i. p. 320. The third generation
+is described by Capt. Yule in his 'Narrative of the Mission to the Court of
+Ava,' 1855, p. 94.
+
+[166] 'Das Ganze der Taubenzucht,' 1837, s. 21, tab. i., fig. 4; s. 24,
+tab. iv., fig. 2.
+
+[167] Kidd's 'Treatise on the Canary,' p. 18.
+
+[168] Charlesworth, 'Mag. of Nat. Hist.,' vol. i., 1837, p. 167.
+
+[169] Dr. Prosper Lucas, 'Hered. Nat.,' tom. ii. p. 713.
+
+[170] 'L'Hered. dans les Maladies,' 1840, p. 135. For Hunter, _see_
+Harlan's 'Med. Researches,' p. 530.
+
+[171] 'L'Hered. Nat.,' tom. ii. p. 850.
+
+[172] Sedgwick, 'Brit. and For. Med.-Chirurg. Review,' April 1861, p. 485.
+I have seen three accounts, all taken from the same original authority
+(which I have not been able to consult), and all differ in the details! but
+as they agree in the main facts, I have ventured to quote this case.
+
+[173] Prosper Lucas, 'Hered. Nat.,' tom. i. p. 400.
+
+[174] Sedgwick, idem, July, 1861, p. 202.
+
+[175] Piorry, p. 109; Prosper Lucas, tom. ii. p. 759.
+
+[176] Prosper Lucas, tom. ii. p. 748.
+
+[177] Prosper Lucas, tom. ii. pp. 678, 700, 702; Sedgwick, idem, April,
+1863, p. 449, and July, 1863, p. 162; Dr. J. Steinan, 'Essay on Hereditary
+Disease,' 1843, pp. 27, 34.
+
+[178] These cases are given by Mr. Sedgwick, on the authority of Dr. H.
+Stewart, in 'Med.-Chirurg. Review,' April, 1863, pp. 449, 477.
+
+[179] 'Hered. Nat.,' tom. ii. p. 852.
+
+[180] Communications to the Board of Agriculture, vol. i. p. 367.
+
+[181] 'Review of Reports, North of England,' 1808, p. 200.
+
+[182] 'Saeugethiere von Paraguay,' 1830, s. 212.
+
+[183] Rengger, 'Saeugethiere,' &c., s. 154.
+
+[184] White, 'Regular Gradation in Man,' p. 146.
+
+[185] Dr. W. F. Edwards, in his 'Characteres Physiolog. des Races
+Humaines,' p. 23, first called attention to this subject, and ably
+discussed it.
+
+[186] Rev. D. Tyerman, and Bennett, 'Journal of Voyages,' 1821-1829, vol.
+i. p. 300.
+
+[187] Mr. S. J. Salter, 'Journal Linn. Soc.,' vol. vi., 1862, p. 71.
+
+[188] Sturm, 'Ueber Racen, &c.,' 1825, s. 107. Bronn, 'Geschichte der
+Natur.,' b. ii. s. 170, gives a table of the proportions of blood after
+successive crosses. Dr. P. Lucas, 'l'Heredite Nat.,' tom. ii. p. 308.
+
+[189] 'Bastarderzeugung,' s. 463, 470.
+
+[190] 'Nova Acta Petrop.,' 1794, p. 393: _see_ also previous volume.
+
+[191] As quoted in the 'True Principles of Breeding,' by C. H. Macknight
+and Dr. H. Madden, 1865, p. 11.
+
+[192] With respect to plants, an admirable essay on this subject (Die
+Geschlechter-Vertheilung bei den Pflanzen: 1867) has lately been published
+by Dr. Hildebrand, who arrives at the same general conclusions as I have
+done.
+
+[193] 'Teoria della Riproduzione Vegetal,' 1816, p. 12.
+
+[194] Verlot, 'Des Varietes,' 1865, p. 72.
+
+[195] Duval-Jouve, 'Bull. Soc. Bot. de France,' tom. x., 1863, p. 194.
+
+[196] Extract of a letter from Sir R. Heron, 1838, given me by Mr. Yarrell.
+With respect to mice, _see_ 'Annal. des Sc. Nat.,' tom. i. p. 180; and I
+have heard of other similar cases. For turtle-doves, Boitard and Corbie,
+'Les Pigeons,' &c., p. 238. For the Game fowl, 'The Poultry Book,' 1866, p.
+128. For crosses of tailless fowls, _see_ Bechstein, 'Naturges. Deutsch.'
+b. iii. s. 403. Bronn, 'Geschichte der Natur,' b. ii. s. 170, gives
+analogous facts with horses. On the hairless condition of crossed South
+American dogs, _see_ Rengger, 'Saeugethiere von Paraguay,' s. 152: but I
+saw in the Zoological Gardens mongrels, from a similar cross, which were
+hairless, quite hairy, or hairy in patches, that is, piebald with hair. For
+crosses of Dorking and other fowls, _see_ 'Poultry Chronicle,' vol. ii. p.
+355. About the crossed pigs, extract of letter from Sir R. Heron to Mr.
+Yarrell. For other cases, _see_ P. Lucas, 'Hered. Nat.,' tom. i. p. 212.
+
+[197] 'Internat. Hort. and Bot. Congress of London,' 1866.
+
+[198] 'Bastarderzeugung,' s. 307. Koelreuter ('Dritte Fortsetszung,' s. 34,
+39), however, obtained intermediate tints from similar crosses in the genus
+Verbascum. With respect to the turnips, _see_ Herbert's 'Amaryllidaceae,'
+1837, p. 370.
+
+[199] 'Nouvelles Archives du Museum,' tom. i. p. 100.
+
+[200] Richardson, 'Pigs,' 1847, pp. 37, 42; S. Sidney's edition of 'Youatt
+on the Pig,' 1860, p. 3.
+
+[201] _See_ Mr. W. C. Spooner's excellent paper on Cross-Breeding, 'Journal
+Royal Agricult. Soc.,' vol. xx., part ii.: _see_ also an equally good
+article by Mr. Ch. Howard, in 'Gardener's Chronicle,' 1860, p. 320.
+
+[202] 'Gardener's Chronicle,' 1857, pp. 649, 652.
+
+[203] 'Bulletin de la Soc. d'Acclimat.,' 1862, tom. ix. p. 463. _See_ also,
+for other cases, MM. Moll and Gayot, 'Du Boeuf,' 1860, p. xxxii.
+
+[204] 'Poultry Chronicle,' vol. ii., 1854, p. 36.
+
+[205] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 58.
+
+[206] 'Gardener's Chronicle,' 1852, p. 765.
+
+[207] Spooner, in 'Journal Royal Agricult. Soc.,' vol. xx., part ii.
+
+[208] _See_ Colin's 'Traite de Phys. Comp. des Animaux Domestiques,' tom.
+ii. p. 536, where this subject is well treated.
+
+[209] 'Les Pigeons,' p. 37.
+
+[210] Vol. i., 1854, p. 101.
+
+[211] 'Cottage Gardener,' 1856, p. 110.
+
+[212] 'Bastarderzeugung,' s. 553.
+
+[213] Dr. Pigeaux, in 'Bull. Soc. d'Acclimat.,' tom. iii., July 1866, as
+quoted in 'Annals and Mag. of Nat. Hist.,' 1867, vol. xx. p. 75.
+
+[214] 'Journal de Physiolog.,' tom. ii., 1859, p. 385.
+
+[215] Dec. 1863, p. 484.
+
+[216] On the Varieties of Wheat, p. 66.
+
+[217] Rengger, 'Saeugethiere von Paraguay,' s. 336.
+
+[218] _See_ a memoir by MM. Lherbette and De Quatrefages, in 'Bull. Soc.
+d'Acclimat.,' tom. viii., July, 1861, p. 312.
+
+[219] For the Norfolk sheep, _see_ Marshall's 'Rural Economy of Norfolk,'
+vol. ii. p. 133. _See_ Rev. L. Landt's 'Description of Faroe,' p. 66. For
+the ancon sheep, _see_ 'Phil. Transact.,' 1813, p. 90.
+
+[220] White's 'Nat. Hist. of Selbourne,' edited by Bennett, p. 39. With
+respect to the origin of the dark-coloured deer, _see_ 'Some Account of
+English Deer Parks,' by E. P. Shirley, Esq.
+
+[221] 'The Dovecote,' by the Rev. E. S. Dixon, p. 155; Bechstein,
+'Naturgesch. Deutschlands,' Band iv., 1795, s. 17.
+
+[222] 'Cattle,' p. 202.
+
+[223] Mr. J. Wilkinson, in 'Remarks addressed to Sir J. Sebright,' 1820, p.
+38.
+
+[224] 'Gardener's Chronicle,' 1858, p. 771.
+
+[225] 'Bastarderzeugung,' s. 87, 169. _See_ also the Table at the end of
+volume.
+
+[226] 'Bastarderzeugung,' s. 87, 577.
+
+[227] 'Kenntniss der Befruchtung,' s. 137; 'Bastarderzeugung,' s. 92, 181.
+On raising the two varieties from seed _see_ s. 307.
+
+[228] 'Bastarderzeugung,' s. 216.
+
+[229] The following facts, given by Koelreuter in his 'Dritte Fortsetzung,'
+s. 34, 39, appear at first sight strongly to confirm Mr. Scott's and
+Gaertner's statements; and to a certain limited extent they do so.
+Koelreuter asserts, from innumerable observations, that insects incessantly
+carry pollen from one species and variety of Verbascum to another; and I
+can confirm this assertion; yet he found that the white and yellow
+varieties of _Verbascum lychnitis_ often grew wild mingled together:
+moreover, he cultivated these two varieties in considerable numbers during
+four years in his garden, and they kept true by seed; but when he crossed
+them, they produced flowers of an intermediate tint. Hence it might have
+thought that both varieties must have a stronger elective affinity for the
+pollen of their own variety than for that of the other; this elective
+affinity, I may add, of each species for its own pollen (Koelreuter,
+'Dritte Forts.,' s. 39, and Gaertner, 'Bastarderz.,' _passim_) being a
+perfectly well-ascertained power. But the force of the foregoing facts is
+much lessened by Gaertner's numerous experiments, for, differently from
+Koelreuter, he never once got ('Bastarderz.,' s. 307) an intermediate tint
+when he crossed the yellow and white flowered varieties of Verbascum. So
+that the fact of the white and yellow varieties keeping true to their
+colour by seed does not prove that they were not mutually fertilised by the
+pollen carried by insects from one to the other.
+
+[230] 'Amaryllidaceae,' 1837, p. 366. Gaertner has made a similar
+observation.
+
+[231] Koelreuter first observed this fact. 'Mem. de l'Acad. St.
+Petersburg,' vol. iii. p. 197. _See_ also C. K. Sprengel, 'Das Entdeckte
+Geheimniss,' s. 345.
+
+[232] Namely, Barbarines, Pastissons, Giraumous: 'Annal. des Sc. Nat.,'
+tom. xxx., 1833, pp. 398 and 405.
+
+[233] 'Memoire sur les Cucurbitaceae,' 1826, pp. 46, 55.
+
+[234] 'Annales des Se. Nat.,' 4th series, tom. vi. M. Naudin considers
+these forms as undoubtedly varieties of _Cucurbita pepo_.
+
+[235] 'Mem. Cucurb.,' p. 8.
+
+[236] 'Zweite Forts.,' s. 53, namely, Nicotiana major vulgaris; (2)
+perennis; (3) Transylvanica; (4) a sub-var. of the last; (5) major latifol.
+fl. alb.
+
+[237] Koelreuter was so much struck with this fact that he suspected that a
+little pollen of _N. glutinosa_ in one of his experiments might have
+accidentally got mingled with that of _var. perennis_, and thus aided its
+fertilising power. But we now know conclusively from Gaertner
+('Bastarderz.,' s. 34, 431) that two kinds of pollen never act _conjointly_
+on a third species; still less will the pollen of a distinct species,
+mingled with a plant's own pollen, if the latter be present in sufficient
+quantity, have any effect. The sole effect of mingling two kinds of pollen
+is to produce in the same capsule seeds which yield plants, some taking
+after the one and some after the other parent.
+
+[238] Mr. Scott has made some observations on the absolute sterility of a
+purple and white primrose (_Primula vulgaris_) when fertilised by pollen
+from the primrose ('Journal of Proc. of Linn. Soc.,' vol. viii., 1864, p.
+98); but these observations require confirmation. I raised a number of
+purple-flowered long-styled seedlings from seed kindly sent me by Mr.
+Scott, and, though they were all some degree sterile, they were much more
+fertile with pollen taken from the common primrose than with their own
+pollen. Mr. Scott has likewise described a red equal-styled cowslip (_P.
+veris_, idem, p. 106), which was found by him to be highly sterile when
+crossed with the common cowslip; but this was not the case with several
+equal-styled red seedlings raised by me from his plant. This variety of the
+cowslip presents the remarkable peculiarity of combining male organs in
+every respect like those of the short-styled form, with female organs
+resembling in function and partly in structure those of the long-styled
+form; so that we have the singular anomaly of the two forms combined in the
+same flower. Hence it is not surprising that these flowers should be
+spontaneously self-infertile in a high degree.
+
+[239] 'Act. Acad. St. Petersburg,' 1780, part ii., pp. 84, 100.
+
+[240] 'Annales des Sc. Nat.,' tom. xxi. (1st series), p. 61.
+
+[241] 'Bull. Bot. Soc. de France,' Dec. 27th, 1861, tom. viii. p. 612.
+
+[242] Quoted by Isid. Geoffroy St. Hilaire, 'Hist. Naturelle Generale,'
+tom. iii. p. 476. Since this MS. has been sent to press a full discussion
+on the present subject has appeared in Mr. Herbert Spencer's 'Principles of
+Biology,' vol. ii. 1867, p. 457 _et seq._
+
+[243] For cats and dogs, &c., _see_ Bellingeri, in 'Annal. des Sc. Nat.,'
+2nd series, Zoolog., tom. xii. p. 155. For ferrets, Bechstein,
+'Naturgeschichte Deutschlands,' Band i., 1801, s. 786, 795. For rabbits,
+ditto, s. 1123, 1131; and Bronn's 'Geschichte der Natur,' B. ii. s. 99. For
+mountain sheep, ditto, s. 102. For the fertility of the wild sow, _see_
+Bechstein's 'Naturgesch. Deutschlands,' B. i., 1801, s. 534; for the
+domestic pig, Sidney's edit. of Youatt on the Pig, 1860, p. 62. With
+respect to Lapland, _see_ Acerbi's 'Travels to the North Cape,' Eng.
+translat., vol. ii. p. 222. About the Highland cows, _see_ Hogg on Sheep,
+p. 263.
+
+[244] For the eggs of _Gallus bankiva_, _see_ Blyth, in 'Annals and Mag. of
+Nat. Hist., 2nd series, vol. i., 1848, p. 456. For wild and tame ducks,
+Macgillivray, 'British Birds,' vol. v. p. 37; and 'Die Enten,' s. 87. For
+wild geese, L. Lloyd, 'Scandinavian Adventures,' vol. ii. 1854, p. 413; and
+for tame geese, 'Ornamental Poultry,' by Rev. E. S. Dixon, p. 139. On the
+breeding of pigeons, Pistor, 'Das Ganze der Taubenzucht,' 1831, s. 46; and
+Boitard and Corbie, 'Les Pigeons,' p. 158. With respect to peacocks,
+according to Temminck ('Hist. Nat. Gen. des Pigeons,' &c., 1813, tom. ii.
+p. 41), the hen lays in India even as many as twenty eggs; but according to
+Jerdon and another writer (quoted in Tegetmeier's 'Poultry Book,' 1866, pp.
+280, 282), she there lays only from four to nine or ten eggs: in England
+she is said, in the 'Poultry Book,' to lay five or six, but another writer
+says from eight to twelve eggs.
+
+[245] 'The Art of Improving the Breed, &c.,' 1809, p. 16.
+
+[246] For Andrew Knight, _see_ A. Walker, on 'Intermarriage,' 1838, p. 227.
+Sir J. Sebright's Treatise has just been quoted.
+
+[247] 'Cattle,' p. 199.
+
+[248] Nathusius, 'Ueber Shorthorn Rindvieh,' 1857, s. 71: _see_ also
+'Gardener's Chronicle,' 1860, p. 270. Many analogous cases are given in a
+pamphlet recently published by Mr. C. Macknight and Dr. H. Madden, 'On the
+True Principles of Breeding;' Melbourne, Australia, 1865.
+
+[249] Mr. Willoughby Wood, in 'Gardener's Chronicle,' 1855, p. 411; and
+1860, p. 270. _See_ the very clear tables and pedigrees given in Nathusius'
+'Rindvieh,' s. 72-77.
+
+[250] Mr. Wright, 'Journal of Royal Agricult. Soc.,' vol. vii., 1846, p.
+204.
+
+[251] Youatt on Cattle, p. 202.
+
+[252] Report British Assoc., Zoolog. Sect., 1838.
+
+[253] Azara, 'Quadrupedes du Paraguay,' tom. ii. pp. 354, 368.
+
+[254] For the case of the Messrs. Brown, _see_ 'Gard. Chronicle,' 1855, p.
+26. For the Foscote flock, 'Gard. Chron.,' 1860, p. 416. For the Naz flock,
+'Bull. de la Soc. d'Acclimat.,' 1860, p. 477.
+
+[255] Nathusius, 'Rindvieh,' s. 65; Youatt on Sheep, p. 495.
+
+[256] 'Gard. Chronicle,' 1861, p. 631.
+
+[257] Lord Somerville, 'Facts on Sheep and Husbandry,' p. 6. Mr. Spooner,
+in 'Journal of Royal Agricult. Soc. of England,' vol. xx., part ii. _See_
+also an excellent paper on the same subject in 'Gard. Chronicle,' 1860, p.
+321, by Mr. Charles Howard.
+
+[258] 'Some Account of English Deer Parks,' by Evelyn P. Shirley, 1867.
+
+[259] 'The Art of Improving the Breed,' &c., p. 13. With respect to Scotch
+deer-hounds, _see_ Scrope's 'Art of Deer Stalking,' pp. 350-353.
+
+[260] 'Cottage Gardener,' 1861, p. 327.
+
+[261] Sidney's edit. of Youatt on the Pig, 1860, p. 30; p. 33, quotation
+from Mr. Druce; p. 29, on Lord Western's case.
+
+[262] 'Journal, Royal Agricult. Soc. of England,' 1846, vol. vii. p. 205.
+
+[263] 'Ueber Rindvieh,' &c., s. 78.
+
+[264] Sidney on the Pig, p. 36. _See_ also note, p. 34. Also Richardson on
+the Pig, 1847, p. 26.
+
+[265] Dr. Dally has published an excellent article (translated in the
+'Anthropolog. Review,' May, 1864, p. 65), criticising all writers who have
+maintained that evil follows from consanguineous marriages. No doubt on
+this side of the question many advocates have injured their cause by
+inaccuracies: thus it has been stated (Devay, 'Du Danger des Mariages,'
+&c., 1862, p. 141) that the marriages of cousins have been prohibited by
+the legislature of Ohio; but I have been assured, in answer to inquiries
+made in the United States, that this statement is a mere fable.
+
+[266] _See_ his most interesting work on the 'Early History of Man,' 1865,
+chap. x.
+
+[267] On Consanguinity in Marriage, in the 'Fortnightly Review,' 1865, p.
+710; Hofacker, 'Ueber die Eigenschaften,' &c.
+
+[268] Sir G. Grey's 'Journal of Expeditions into Australia,' vol. ii. p.
+243; and Dobrizhoffer, 'On the Abipones of South America.'
+
+[269] 'The Art of Improving the Breed,' p. 13.
+
+[270] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 245.
+
+[271] 'Journal Royal Agricult. Soc.' 1846, vol. vii. p. 205; _see_ also
+Ferguson on the Fowl, pp. 83, 317; _see_ also 'The Poultry Book,' by
+Tegetmeier, 1866, p. 135, with respect to the extent to which cock-fighters
+found that they could venture to breed in-and-in, viz., occasionally a hen
+with her own son; "but they were cautious not to repeat the in-and-in
+breeding."
+
+[272] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 79.
+
+[273] 'The Poultry Chronicle,' 1854, vol. i. p. 43.
+
+[274] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 79.
+
+[275] 'The Poultry Chronicle,' vol. i. p. 89.
+
+[276] 'The Poultry Book,' 1866, p. 210.
+
+[277] Ibid, 1866, p. 167; and 'Poultry Chronicle,' vol. iii., 1855, p. 15.
+
+[278] 'A Treatise on Fancy Pigeons,' by J. M. Eaton, p. 56.
+
+[279] 'The Pigeon Book,' p. 46.
+
+[280] 'Das Ganze der Taubenzucht,' 1837, s. 18.
+
+[281] 'Les Pigeons,' 1824, p. 35.
+
+[282] 'Proc. Entomolog. Soc.,' Aug. 6th, 1860, p. 126.
+
+[283] 'Journal of Horticulture,' 1861, pp. 39, 77, 158; and 1864, p. 206.
+
+[284] 'Beitraege zur Kenntniss der Befruchtung,' 1844, s. 366.
+
+[285] 'Amaryllidaceae,' p. 371.
+
+[286] 'De la Fecondation,' 2nd edit., 1862, p. 79.
+
+[287] 'Memoire sur les Cucurbitacees,' pp. 36, 28, 30.
+
+[288] Loudon's 'Gard. Mag.,' vol. viii., 1832, p. 52.
+
+[289] 'Transact. Hort. Soc.,' vol. i. p. 25.
+
+[290] 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. vi. p. 189.
+
+[291] 'Philosophical Transactions,' 1799, p. 200.
+
+[292] 'Ueber die Bastarderzeugung,' 1828, s. 32, 33. For Mr. Chaundy's
+case, _see_ Loudon's 'Gard. Mag.,' vol. vii., 1831, p. 696.
+
+[293] 'Gardener's Chron.,' 1846, p. 601.
+
+[294] 'Philosoph. Transact.,' 1799, p. 201.
+
+[295] Quoted in 'Bull. Bot. Soc. France,' vol. ii., 1855, p. 327.
+
+[296] Gaertner, 'Bastarderzeugung,' s. 259, 518, 526 _et seq._
+
+[297] 'Fortsetzung,' 1763, s. 29; 'Dritte Fortsetzung,' s. 44, 96; 'Act.
+Acad. St. Petersburg,' 1782, part ii., p. 251; 'Nova Acta,' 1793, pp. 391,
+394; 'Nova Acta,' 1795, pp. 316, 323.
+
+[298] 'Die Bastardbefruchtung,' &c., 1865, s. 31, 41, 42.
+
+[299] Max Wichura fully accepts this view ('Bastardbefruchtung,' s. 43), as
+does the Rev. M. J. Berkeley, in 'Journal of Hort. Soc.,' Jan. 1866, p. 70.
+
+[300] 'Bastarderzeugung,' s. 394, 526, 528.
+
+[301] Koelreuter,' Nova Acta,' 1795, p. 316.
+
+[302] Gaertner, 'Bastarderzeugung,' s. 430.
+
+[303] 'Botanische Zeitung,' Jan. 1864, s. 3.
+
+[304] 'Monatsbericht Akad. Wissen,' Berlin, 1866, s. 372.
+
+[305] International Hort. Congress, London, 1866.
+
+[306] 'Proc. Bot. Soc. of Edinburgh,' May, 1863: these observations are
+given in abstract, and others are added, in the 'Journal of Proc. of Linn.
+Soc.,' vol. viii. Bot., 1864, p. 162.
+
+[307] Prof. Lecoq, 'De la Fecondation,' 2nd edit., 1862, p. 76.
+
+[308] 'Bastarderzeugung,' s. 64, 357.
+
+[309] Idem, s. 357.
+
+[310] 'Zweite Fortsetzung,' s. 10; 'Dritte Fort.,' s. 40.
+
+[311] Duvernoy, quoted by Gaertner, 'Bastarderzeugung,' s. 334.
+
+[312] 'Gardner's Chronicle,' 1846, p. 183.
+
+[313] 'Transact. Hort. Soc.,' vol. vii., 1830, p. 95.
+
+[314] Prof. Lecoq, 'De la Fecondation,' 1845, p. 70; Gaertner,
+'Bastarderzeugung,' s. 64.
+
+[315] 'Gardener's Chron.' 1866, p. 1068.
+
+[316] 'Journal of Proc. of Linn. Soc.,' vol. viii., 1864, p. 168.
+
+[317] 'Amaryllidaceae,' 1837, p. 371; 'Journal of Hort. Soc.,' vol. ii.,
+1847, p. 19.
+
+[318] Loudon's 'Gardener's Magazine,' vol. xi., 1835, p. 260.
+
+[319] 'Gardener's Chronicle,' 1850, p. 470.
+
+[320] 'Journal Hort. Soc., vol. v. p. 135. The seedlings thus raised were
+given to the Hort. Soc.; but I find, on inquiry, that they unfortunately
+died the following winter.
+
+[321] Mr. D. Beaton, in 'Journal of Hort.,' 1861, p. 453. Lecoq, however
+('De la Fecond.,' 1862, p. 369), states that this hybrid is descended from
+_G. psittacinus_ and _cardinalis_; but this is opposed to Herbert's
+experience, who found that the former species could not be crossed.
+
+[322] This is the conclusion of Prof. Devay, 'Du Danger des Mariages
+Consang.,' 1862, p. 97. Virchow quotes, in the 'Deutsche Jahrbuecher,'
+1863, s. 354, some curious evidence on half the cases of a peculiar form of
+blindness occurring in the offspring from near relations.
+
+[323] For England, _see_ below. For Germany, _see_ Metzger,
+'Getreidearten,' 1841, s. 63. For France, Loiseleur-Deslongchamps ('Consid.
+sur les Cereales,' 1843, p. 200) gives numerous references on this subject.
+For Southern France, _see_ Godron, 'Florula Juvenalis,' 1854, p. 28.
+
+[324] 'A general Treatise of Husbandry,' vol. iii. p. 58.
+
+[325] 'Gardener's Chronicle and Agricult. Gazette,' 1858, p. 247; and for
+the second statement, idem, 1850, p. 702. On this same subject, _see_ also
+Rev. D. Walker's 'Prize Essay of Highland Agricult. Soc.,' vol. ii. p. 200.
+Also Marshall's 'Minutes of Agriculture,' November, 1775.
+
+[326] Oberlin's 'Memoirs,' Eng. translat., p. 73. For Lancashire, _see_
+Marshall's 'Review of Reports,' 1808, p. 295.
+
+[327] 'Cottage Gardener,' 1856, p. 186. For Mr. Robson's subsequent
+statements, _see_ 'Journal of Horticulture,' Feb. 18, 1866, p. 121. For Mr.
+Abbey's remarks on grafting, &c., idem, July 18, 1865, p. 44.
+
+[328] 'Mem. de l'Acad. des Sciences,' 1790, p. 209.
+
+[329] 'On the Varieties of Wheat,' p. 52.
+
+[330] Mr. Spencer has fully and ably discussed this whole subject in his
+'Principles of Biology,' 1864, vol. ii. ch. x. In the first edition of my
+'Origin of Species,' 1859, p. 267, I spoke of the good effects from slight
+changes in the conditions of life and from cross-breeding, and of the evil
+effects from great changes in the conditions and from crossing widely
+distinct forms, as a series of facts "connected together by some common but
+unknown bond, which is essentially related to the principle of life."
+
+[331] 'Essais de Zoologie Generale,' 1841, p. 256.
+
+[332] Du Rut, 'Annales du Museum,' 1807, tom. ix. p. 120.
+
+[333] 'Saeugethiere von Paraguay,' 1830, s. 49, 106, 118, 124, 201, 208,
+249, 265, 327.
+
+[334] 'The Naturalist on the Amazons,' 1863, vol. i. pp. 99, 193; vol. ii.
+p. 113.
+
+[335] 'Embassy to the Court of Ava,' vol. i. p. 534.
+
+[336] 'Journal,' vol. i. p. 213.
+
+[337] 'Saeugethiere,' s. 327.
+
+[338] On the Breeding of the larger Felidae, 'Proc. Zoolog. Soc.,' 1861, p.
+140.
+
+[339] Sleeman's 'Rambles in India,' vol. ii. p. 10.
+
+[340] Wiegmann's 'Archif fuer Naturgesch.,' 1837, s. 162.
+
+[341] Rengger, 'Saeugethiere,' &c., s. 276. On the parentage of the
+guinea-pig, _see_ also Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gen.'
+
+[342] Although the existence of the _Leporides_, as described by Dr. Broca
+('Journal de Phys.,' tom. ii. p. 370), is now positively denied, yet Dr.
+Pigeaux ('Annals and Mag. of Nat. Hist.,' vol. xx., 1867, p. 75) affirms
+that the hare and rabbit have produced hybrids.
+
+[343] 'Quadrupeds of North America,' by Audubon and Bachman, 1846, p. 268.
+
+[344] Loudon's 'Mag. of Nat. Hist.,' vol. ix., 1836, p. 571; Audubon and
+Bachman's 'Quadrupeds of North America,' p. 221.
+
+[345] Flourens, 'De l'Instinct,' &c., 1845, p. 88.
+
+[346] _See_ 'Annual Reports Zoolog. Soc.,' 1855, 1858, 1863, 1864; 'Times'
+newspaper, Aug. 10th, 1847; Flourens, 'De l'Instinct,' p. 85.
+
+[347] 'Saeugethiere,' &c., s. 34, 49.
+
+[348] Art. Brazil, 'Penny Cyclop.,' p. 363.
+
+[349] 'The Naturalist on the River Amazon,' vol. i. p. 99.
+
+[350] 'Encyclop. of Rural Sports,' p. 691.
+
+[351] According to Sir A. Burnes ('Cabool,' &c., p. 51), eight species are
+used for hawking in Scinde.
+
+[352] Loudon's 'Mag. of Nat. Hist.,' vol. vi., 1833, p. 110.
+
+[353] F. Cuvier, 'Annal. du Museum,' tom. ix. p. 128.
+
+[354] 'The Zoologist,' vol. vii.-viii., 1849-50, p. 2648.
+
+[355] Knox, 'Ornithological Rambles in Sussex,' p. 91.
+
+[356] 'The Zoologist,' vol. vii.-viii., 1849-50, p. 2566; vol. ix.-x.,
+1851-2, p. 3207.
+
+[357] Bechstein, 'Naturgesch. der Stubenvoegel,' 1840, s. 20.
+
+[358] 'Ornithological Biography,' vol. v. p. 517.
+
+[359] A case is recorded in 'The Zoologist,' vol. i.-ii., 1843-45, p. 453.
+For the siskin breeding, vol. iii.-iv., 1845-46, p. 1075. Bechstein,
+'Stubenvoegel,' s. 139, speaks of bullfinches making nests, but rarely
+producing young.
+
+[360] Yarrell's 'Hist. British Birds,' 1839, vol. i. p. 412.
+
+[361] Loudon's 'Mag. of Nat. History,' vol. ix., 1836, p. 347.
+
+[362] 'Memoires du Museum d'Hist. Nat.,' tom. x. p. 314: five cases of
+parrots breeding in France are here recorded. _See_, also, 'Report Brit.
+Assoc. Zoolog.,' 1843.
+
+[363] 'Stubenvoegel,' s. 105, 83.
+
+[364] Dr. Hancock remarks ('Charlesworth's Mag. of Nat. Hist.,' vol. ii.,
+1838, p. 492), "it is singular that, amongst the numerous useful birds that
+are indigenous to Guiana, none are found to propagate among the Indians;
+yet the common fowl is reared in abundance throughout the country."
+
+[365] 'A Week at Port Royal,' 1855, p. 7.
+
+[366] Audubon, 'American Ornithology,' vol. v. pp. 552, 557.
+
+[367] Moubray on Poultry, 7th edit., p. 133.
+
+[368] Temminck, 'Hist. Nat. Gen. des Pigeons,' &c., 1813, tom. iii. pp.
+288, 382; 'Annals and Mag. of Nat. Hist.,' vol. xii., 1843, p. 453. Other
+species of partridge have occasionally bred; as the red-legged (_P.
+rubra_), when kept in a large court in France (_see_ 'Journal de Physique,'
+tom. xxv. p. 294), and in the Zoological Gardens in 1856.
+
+[369] Rev. E. S. Dixon, 'The Dovecote,' 1851, pp. 243-252.
+
+[370] Temminck, 'Hist. Nat. Gen. des Pigeons,' &c., tom. ii. pp. 456, 458;
+tom. iii. pp. 2, 13, 47.
+
+[371] Bates, 'The Naturalist on the Amazons,' vol. i. p. 193; vol. ii. p.
+112.
+
+[372] Temminck, 'Hist. Nat. Gen.,' &c., tom. iii. p. 125. For _Tetrao
+urogallus_, _see_ L. Lloyd, 'Field Sports of North of Europe,' vol. i. pp.
+287, 314; and 'Bull. de la Soc. d'Acclimat.,' tom. vii., 1860, p. 600. For
+_T. Scoticus_, Thompson, 'Nat. Hist. of Ireland,' vol. ii., 1850, p. 49.
+For _T. cupido_, 'Boston Journal of Nat. Hist.,' vol. iii. p. 199.
+
+[373] Marcel de Serres, 'Annales des Sci. Nat.,' 2nd series, Zoolog., tom.
+xiii. p. 175.
+
+[374] Dr. Hancock, in 'Charlesworth's Mag. of Nat. Hist.' vol. ii., 1838,
+p. 491; R. Hill, 'A Week at Port Royal,' p. 8; 'Guide to the Zoological
+Gardens,' by P. L. Sclater, 1859, pp. 11, 12; 'The Knowsley Menagerie,' by
+Dr. Gray, 1846, pl. xiv.; E. Blyth, 'Report Asiatic Soc. of Bengal,' May,
+1855.
+
+[375] Prof. Newton, in 'Proc. Zoolog. Soc.,' 1860, p. 336.
+
+[376] 'The Dovecote and Aviary,' p. 428.
+
+[377] 'Ornithological Biography,' vol. iii. p. 9.
+
+[378] 'Geograph. Journal,' vol. xiii., 1844, p. 32.
+
+[379] Loudon's 'Mag. of Nat. Hist.,' vol. v., 1832, p. 153.
+
+[380] 'Zoologist,' vols. v.-vi., 1847-48, p. 1660.
+
+[381] 'Transact. Entomolog. Soc.,' vol.  iv., 1845, p. 60.
+
+[382] 'Transact. Linn. Soc.,' vol. vii. p. 40.
+
+[383] _See_ an interesting paper by Mr. Newman, in the 'Zoologist,' 1857,
+p. 5764; and Dr. Wallace, in 'Proc. Entomolog. Soc.,' June 4th, 1860, p.
+119.
+
+[384] Yarrell's 'British Birds,' vol. i. p. 506; Bechstein, 'Stubenvoegel,'
+s. 185; 'Philosoph. Transact.,' 1772, p. 271. Bronn ('Geschichte der
+Natur,' Band ii. s. 96) has collected a number of cases. For the case of
+the deer, _see_ 'Penny Cyclop.,' vol. viii. p. 350.
+
+[385] 'Journal de Physiologie,' tom. ii. p. 347.
+
+[386] For additional evidence on this subject, _see_ F. Cuvier, in 'Annales
+du Museum,' tom. xii. p. 119.
+
+[387] Numerous instances could be given. Thus Livingstone ('Travels,' p.
+217) states that the King of the Barotse, an inland tribe which never had
+any communication with white men, was extremely fond of taming animals, and
+every young antelope was brought to him. Mr. Galton informs me that the
+Damaras are likewise fond of keeping pets. The Indians of South America
+follow the same habit. Capt. Wilkes states that the Polynesians of the
+Samoan Islands tamed pigeons; and the New Zealanders, as Mr. Mantell
+informs me, kept various kinds of birds.
+
+[388] For analogous cases with the fowl, _see_ Reaumur, 'Art de faire
+Eclorre,' &c., 1749, p. 243; and Col. Sykes, in 'Proc. Zoolog. Soc.,' 1832,
+&c. With respect to the fowl not breeding in northern regions, _see_
+Latham's 'Hist. of Birds,' vol. viii., 1823, p. 169.
+
+[389] 'Mem. par divers Savans, Acad. des Sciences,' tom. vi., 1835, p. 347.
+
+[390] Youatt on Sheep, p. 181.
+
+[391] J. Mills, 'Treatise on Cattle,' 1776, p. 72.
+
+[392] Bechstein, 'Stubenvoegel,' s. 242.
+
+[393] Crawfurd's 'Descriptive Dict. of the Indian Islands,' 1856, p. 145.
+
+[394] 'Bull. de la Soc. Acclimat., tom. ix., 1862, pp. 380, 384.
+
+[395] For pigeons, _see_ Dr. Chapuis, 'Le Pigeon Voyageur Belge,' 1865, p.
+66.
+
+[396] 'Swedish Acts,' vol. i., 1739, p. 3. Pallas makes the same remark in
+his Travels (Eng. translat.), vol. i. p. 292.
+
+[397] A. Kerner, 'Die Cultur der Alpenflanzen,' 1864, s. 139; Watson's
+'Cybele Britannica,' vol. i. p. 131; Mr. D. Cameron, also, has written on
+the culture of Alpine plants in 'Gard. Chronicle,' 1848, pp. 253, 268, and
+mentions a few which seed.
+
+[398] 'Beitraege zur Kenntniss der Befruchtung,' 1844, s. 333.
+
+[399] 'Nova Acta Petrop.,' 1793, p. 391.
+
+[400] 'Cottage Gardener,' 1856, pp. 44, 109.
+
+[401] Dr. Herbert, 'Amaryllidaceae,' p. 176.
+
+[402] Gaertner, 'Beitraege zur Kenntniss,' &c., s. 560, 564.
+
+[403] 'Gardener's Chronicle,' 1844, p. 215; 1850, p. 470.
+
+[404] 'Beitraege zur Kenntniss,' &c., s. 252, 333.
+
+[405] 'Journal of Hort. Soc.,' vol. ii. 1847, p. 83.
+
+[406] 'Beitraege zur Kenntniss,' &c., s. 117 _et seq._; Koelreuter, 'Zweite
+Fortsetzung,' s. 10, 121; 'Dritte Fortsetzung,' s. 57. Herbert,
+'Amaryllidaceae,' p. 355. Wiegmann, 'Ueber die Bastarderzeugung,' s. 27.
+
+[407] 'Bastarderzeugung,' s. 356.
+
+[408] 'Teoria della Riproduzione,' 1816, p. 84; 'Traite du Citrus,' 1811,
+p. 67.
+
+[409] Mr. C. W. Crocker, in 'Gard. Chronicle,' 1861, p. 1092.
+
+[410] Verlot, 'Des Varietes,' 1865, p. 80.
+
+[411] Verlot, idem, p. 88.
+
+[412] Prof. Allman, Brit. Assoc., quoted in the 'Phytologist,' vol. ii. p.
+483. Prof. Harvey, on the authority of Mr. Andrews, who discovered the
+plant, informed me that this monstrosity could be propagated by seed. With
+respect to the poppy, _see_ Prof. Goeppert, as quoted in 'Journal of
+Horticulture,' July 1st, 1863, p. 171.
+
+[413] 'Comptes Rendus,' Dec. 19th, 1864, p. 1039.
+
+[414] 'Gardener's Chronicle,' 1866, p. 681.
+
+[415] 'Theory of Horticulture,' p. 333.
+
+[416] Mr. Fairweather, in 'Transact. Hort. Soc.,' vol. iii. p. 406; Bosse,
+quoted by Bronn, 'Geschichte der Natur,' B. ii. s. 77. On the effects of
+the removal of the anthers, _see_ Mr. Leitner, in Silliman's 'North
+American Journ. of Science,' vol. xxiii. p. 47; and Verlot, 'Des Varietes,'
+1865, p. 84.
+
+[417] Lindley's 'Theory of Horticulture,' p. 333.
+
+[418] 'Gardener's Chronicle,' 1865, p. 626; 1866, pp. 290, 730; and Verlot,
+'Des Varietes,' p. 75.
+
+[419] 'Gardener's Chronicle,' 1843, p. 628. In this article I suggested the
+following theory on the doubleness of flowers.
+
+[420] Quoted by Gaertner, 'Bastarderzeugung,' s. 567.
+
+[421] 'Gardener's Chronicle,' 1866, p. 901.
+
+[422] Lindley, 'Theory of Horticulture,' p. 175-179; Godron, 'De l'Espece,'
+tom. i. p. 106: Pickering, 'Races of Man;' Gallesio, 'Teoria della
+Riproduzione,' 1816, p. 101-110. Meyen ('Reise um Erde,' Th. ii. s. 214)
+states that at Manilla one variety of the banana is full of seeds; and
+Chamisso (Hooker's 'Bot. Misc.,' vol. i. p. 310) describes a variety of the
+bread-fruit in the Mariana Islands with small fruit, containing seeds which
+are frequently perfect. Burnes, in his 'Travels in Bokhara,' remarks on the
+pomegranate seeding in Mazenderan, as a remarkable peculiarity.
+
+[423] Ingledew, in 'Transact. of Agricult. and Hort. Soc. of India,' vol.
+ii.
+
+[424] 'De la Fecondation,' 1862, p. 308.
+
+[425] Hooker's 'Bot. Misc.,' vol. i. p. 99; Gallesio, 'Teoria della
+Riproduzione,' p. 110.
+
+[426] 'Transact. Linn. Soc.,' vol. xvii. p. 563.
+
+[427] Godron, 'De l'Espece,' tom. ii. p. 106; Herbert on Crocus, in
+'Journal of Hort. Soc.,' vol. i., 1846, p. 254.--Dr. Wight, from what he
+has seen in India, believes in this view; 'Madras Journal of Lit. and
+Science,' vol. iv., 1836, p. 61.
+
+[428] Wahlenberg specifies eight species in this state on the Lapland Alps:
+_see_ Appendix to Linnaeus' 'Tour in Lapland,' translated by Sir J. E.
+Smith, vol. ii. pp. 274-280.
+
+[429] 'Travels in North America,' Eng. translat., vol. iii. p. 175.
+
+[430] With respect to the ivy and Acorus, _see_ Dr. Bromfield in the
+'Phytologist,' vol. iii. p. 376. _See_ also Lindley and Vaucher on the
+Acorus.
+
+[431] 'Annal. des Sc. Nat.,' 3rd series, Zool., tom. iv. p. 280. Prof.
+Decaisne refers also to analogous cases with mosses and lichens near Paris.
+
+[432] Mr. Tuckerman, in Silliman's 'American Journal of Science,' vol. xlv.
+p. 41.
+
+[433] Sir J. E. Smith, 'English Flora,' vol. i. p. 339.
+
+[434] G. Planchon, 'Flora de Montpellier,' 1864, p. 20.
+
+[435] On the non-production of seeds in England _see_ Mr. Crocker, in
+'Gardener's Weekly Magazine,' 1852, p. 70; Vaucher, 'Hist. Phys. Plantes
+d'Europe,' tom. i. p. 33; Lecoq, 'Geograph. Bot. de l'Europe,' tom. iv. p.
+466; Dr. D. Clos, in 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. xvii.,
+1852, p. 129: this latter author refers to other analogous cases. On the
+non-production of pollen by this Ranunculus _see_ Chatin, in 'Comptes
+Rendus,' June 11th, 1866.
+
+[436] 'Bastarderzeugung,' s. 565. Koelreuter ('Dritte Fortsetzung,' s. 73,
+87, 119) also shows that when two species, one single and the other double,
+are crossed, the hybrids are apt to be extremely double.
+
+[437] 'Teoria della Riproduzione Veg.,' 1816, p. 73.
+
+[438] 'Bastarderzeugung,' s. 573.
+
+[439] Ibid., s. 527.
+
+[440] 'Transactions Phil. Soc.,' 1799, p. 202. For Koelreuter, _see_ 'Mem.
+de l'Acad. de St. Petersbourg,' tom. iii., 1809 (published 1811), p. 197.
+In reading C. K. Sprengel's remarkable work, 'Das entdeckte Geheimniss,'
+&c., 1793, it is curious to observe how often this wonderfully acute
+observer failed to understand the full meaning of the structure of the
+flowers which he has so well described, from not always having before his
+mind the key to the problem, namely, the good derived from the crossing of
+distinct individual plants.
+
+[441] This abstract was published in the fourth edition (1866) of my
+'Origin of Species;' but as this edition will be in the hands of but few
+persons, and as my original observations on this point have not as yet been
+published in detail, I have ventured here to reprint the abstract.
+
+[442] The term _unconscious selection_ has been objected to as a
+contradiction: but _see_ some excellent observations on this head by Prof.
+Huxley ('Nat. Hist. Review,' Oct. 1864, p. 578), who remarks that when the
+wind heaps up sand-dunes it sifts and _unconsciously selects_ from the
+gravel on the beach grains of sand of equal size.
+
+[443] Sheep, 1838, p. 60.
+
+[444] Mr. J. Wright on Shorthorn Cattle, in 'Journal of Royal Agricult.
+Soc.,' vol. vii. pp. 208, 209.
+
+[445] H. D. Richardson on Pigs, 1817, p. 44.
+
+[446] 'Journal of R. Agricult. Soc.,' vol. i. p. 24.
+
+[447] Sheep, pp. 520, 319.
+
+[448] Loudon's 'Mag. of Nat. Hist.,' vol. viii., 1835, p. 618.
+
+[449] 'A Treatise on the Art of Breeding the Almond Tumbler,' 1851, p. 9.
+
+[450] 'Recreations in Agriculture,' vol. ii. p. 409.
+
+[451] Youatt on Cattle, pp. 191, 227.
+
+[452] Ferguson, 'Prize Poultry,' 1854, p. 208.
+
+[453] Wilson, in 'Transact. Highland Agricult. Soc.,' quoted in 'Gard.
+Chronicle,' 1844, p. 29.
+
+[454] Simmonds, quoted in 'Gard. Chronicle,' 1855, p. 637. And for the
+second quotation, _see_ Youatt on Sheep, p. 171.
+
+[455] Robinet, 'Vers a Soie,' 1848, p. 271.
+
+[456] Quatrefages, 'Les Maladies du Ver a Soie,' 1859, p. 101.
+
+[457] M. Simon, in 'Bull. de la Soc. d'Acclimat.,' tom. ix., 1862, p. 221.
+
+[458] 'The Poultry Chronicle,' vol. i., 1854, p. 607.
+
+[459] J. M. Eaton, 'A Treatise on Fancy Pigeons,' 1852, p. xiv., and 'A
+Treatise on the Almond Tumbler,' 1851, p. 11.
+
+[460] 'Journal Royal Agricultural Soc.,' vol. vi. p. 22.
+
+[461] 'Poultry Chronicle,' vol. ii., 1855, p. 596.
+
+[462] Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gen.,' tom. iii. p. 254.
+
+[463] 'Gardener's Chronicle,' 1850, p. 198.
+
+[464] 'Transact. Hort. Soc.,' vol. vi. p. 152.
+
+[465] 'Journal of Horticulture,' 1862, p. 369.
+
+[466] 'Transact. Hort. Soc.,' vol. iv. p. 381.
+
+[467] 'Transact. Hort. Soc.,' vol. iv. p. 285.
+
+[468] Rev. W. Bromehead, in 'Gard. Chronicle,' 1857, p. 550.
+
+[469] 'Gard. Chronicle,' 1862, p. 721.
+
+[470] Dr. Anderson, in 'The Bee,' vol. vi. p. 96; Mr. Barnes, in 'Gard.
+Chronicle,' 1844, p. 476.
+
+[471] Godron, 'De l'Espece,' 1859, tom. ii. p. 69; 'Gard. Chronicle,' 1854,
+p. 258.
+
+[472] On Sheep, p. 18.
+
+[473] Volz, 'Beitraege zur Kulturgeschichte,' 1852, s. 47.
+
+[474] Mitford's 'History of Greece,' vol. i. p. 73.
+
+[475] Dr. Dally, translated in 'Anthropological Review,' May 1864, p. 101.
+
+[476] Volz, 'Beitraege,' &c., 1852, s. 80.
+
+[477] 'History of the World,' ch. 45.
+
+[478] 'Gardener's Chronicle,' 1848, p. 323.
+
+[479] Reynier, 'De l'Economie des Celtes,' 1818, pp. 487, 503.
+
+[480] Le Couteur on Wheat, p. 15.
+
+[481] Michel, 'Des Haras,' 1861, p. 84.
+
+[482] Sir W. Wilde, an 'Essay on Unmanufactured Animal Remains,' &c., 1860,
+p. 11.
+
+[483] Col. Hamilton Smith, 'Nat. Library,' vol. xii., Horses, pp. 135, 140.
+
+[484] Michel, 'Des Haras,' p. 90.
+
+[485] Mr. Baker, 'History of the Horse,' Veterinary, vol. xiii. p. 423.
+
+[486] M. l'Abbe Carlier, in 'Journal de Physique,' vol. xxiv., 1784, p.
+181: this memoir contains much information on the ancient selection of
+sheep; and is my authority for rams not being killed young in England.
+
+[487] 'Gardener's Chronicle,' 1843, p. 389.
+
+[488] Communications to Board of Agriculture, quoted in Dr. Darwin's
+'Phytologia,' 1800, p. 451.
+
+[489] 'Memoire sur les Chinois,' 1786, tom. xi. p. 55; tom. v. p. 507.
+
+[490] 'Recherches sur l'Agriculture des Chinois,' par L.
+D'Hervey-Saint-Denys, 1850, p. 229. With respect to Khang-hi, _see_ Huc's
+'Chinese Empire,' p. 311.
+
+[491] Anderson, in 'Linn. Transact.,' vol. xii. p. 253.
+
+[492] 'Mem. de l'Acad.' (divers savans), tom. vi., 1835, p. 333.
+
+[493] 'Des Quadrupedes du Paraguay,' 1801, tom. ii. p. 333, 371.
+
+[494] 'The Great Sahara,' by the Rev. H. B. Tristram, 1860, p. 238.
+
+[495] Pallas, 'Act. Acad. St. Petersburg,' 1777, p. 249; Moorcroft and
+Trebeck, 'Travels in the Himalayan Provinces,' 1841.
+
+[496] Quoted from Raffles, in the 'Indian Field,' 1859, p. 196; for Varro,
+_see_ Pallas, _ut supra_.
+
+[497] Erman's 'Travels in Siberia,' Eng. translat., vol. i. p. 453.
+
+[498] _See_ also 'Journal of R. Geograph. Soc.,' vol. xiii. part i. p. 65.
+
+[499] Livingstone's 'First Travels,' pp. 191, 439, 565; _see_ also
+'Expedition to the Zambesi,' 1865, p. 465, for an analogous case respecting
+a good breed of goats.
+
+[500] Andersson's 'Travels in South Africa,' pp. 232, 318, 319.
+
+[501] Dr. Vavasseur, in 'Bull. de la Soc. d'Acclimat.,' tom. viii., 1861,
+p. 136.
+
+[502] 'The Natural History of Dee Side,' 1855, p. 476.
+
+[503] 'Bull. de la Soc. d'Acclimat.,' tom. vii., 1860, p. 457.
+
+[504] 'Cattle,' p. 48.
+
+[505] Livingstone's Travels, p. 576; Andersson, 'Lake Ngami,' 1856, p. 222.
+With respect to the sale in Kaffraria, _see_ 'Quarterly Review,' 1860, p.
+139.
+
+[506] 'Memoire sur les Chinois' (by the Jesuits), 1786, tom. xi. p. 57.
+
+[507] F. Michel, 'Des Haras,' pp. 47, 50.
+
+[508] Col. Hamilton Smith, Dogs, in 'Nat. Lib.,' vol. x. p. 103.
+
+[509] Azara, 'Quadrupedes du Paraguay,' tom. ii. p. 324.
+
+[510] Sidney's edit. of Youatt, 1860, pp. 24, 25.
+
+[511] 'Rural Economy of Yorkshire,' vol. ii. p. 182.
+
+[512] Moll et Gayot, 'Du Boeuf,' 1860, p. 547.
+
+[513] 'The India Sporting Review,' vol. ii. p. 181; 'The Stud Farm,' by
+Cecil, p. 58.
+
+[514] 'The Horse,' p. 22.
+
+[515] 'History of England,' vol. i. p. 316.
+
+[516] 'Uber Bestaendigkeit der Arten.'
+
+[517] Youatt on Sheep, p. 315.
+
+[518] 'Ueber Shorthorn Rindvieh,' 1857, s. 51.
+
+[519] Low, 'Domesticated Animals,' 1845, p. 363.
+
+[520] 'Quarterly Review,' 1849, p. 392.
+
+[521] H. von Nathusius, 'Vorstudien ... Schweineschaedel,' 1864, s. 140.
+
+[522] _See_ also Dr. Christ, in 'Ruetimeyer's Pfahlbauten,' 1861, s. 226.
+
+[523] The passage is given 'Bull. Soc. d'Acclimat.,' 1858, p. 11.
+
+[524] 'Journal of Horticulture,' 1862, p. 394.
+
+[525] 'Gardener's Chronicle,' 1857, p. 85.
+
+[526] _See_ Mr. Wildman's address to the Floricult. Soc., in 'Gardener's
+Chronicle,' 1843, p. 86.
+
+[527] 'Journal of Horticulture,' Oct. 24th, 1865, p. 239.
+
+[528] Prescott's 'Hist. of Mexico,' vol. ii. p. 61.
+
+[529] Sageret, 'Pomologie Physiologique,' 1830, p. 47; Gallesio, 'Teoria
+della Riproduzione,' 1816, p. 88; Godron, 'De l'Espece,' 1859, tom. ii. pp.
+63, 67, 70. In my tenth and eleventh chapters I have given details on the
+potato; and I can confirm similar remarks with respect to the onion. I have
+also shown how far Naudin concurs in regard to the varieties of the melon.
+
+[530] Godron, 'De l'Espece,' tom. ii. p. 27.
+
+[531] 'The Anthropological Treatises of Blumenbach,' 1865, p. 292.
+
+[532] Mr. J. J. Murphy in his opening address to the Belfast Nat. Hist.
+Soc., as given in the Belfast Northern Whig, Nov. 19, 1866. Mr. Murphy here
+follows the line of argument against my views previously and more
+cautiously given by the Rev. C. Pritchard, Pres. Royal Astronomical Soc.,
+in his sermon (Appendix, p. 33) preached before the British Association at
+Nottingham, 1866.
+
+[533] On the Vision of Fishes and Amphibia, translated in 'Annals and Mag.
+of Nat. Hist.,' vol. xviii., 1866, p. 469.
+
+[534] Fourth edition, 1866, p. 215.
+
+[535] Quoted by Youatt on Sheep, p. 325. _See_ also Youatt on Cattle, pp.
+62, 69.
+
+[536] MM. Lherbette and De Quatrefages, in 'Bull. Soc. Acclimat.,' tom.
+viii., 1861, p. 311.
+
+[537] 'The Poultry Book,' 1866, p. 123.
+
+[538] Youatt on Sheep, p. 312.
+
+[539] 'Treatise on the Almond Tumbler,' 1851, p. 33.
+
+[540] Dr. Heusinger, 'Wochenschrift fuer die Heilkunde,' Berlin, 1846, s.
+279.
+
+[541] Youatt on the Dog, p. 232.
+
+[542] 'The Fruit-trees of America,' 1845, p. 270: for peaches, p. 466.
+
+[543] 'Proc. Royal Soc. of Arts and Sciences of Mauritius,' 1852, p. cxxxv.
+
+[544] 'Gardener's Chronicle,' 1856, p. 379.
+
+[545] Quatrefages, 'Maladies Actuelles du Ver a Soie,' 1859, pp. 12, 214.
+
+[546] 'Gardener's Chronicle,' 1851, p. 595.
+
+[547] 'Journal of Horticulture,' 1862, p. 476.
+
+[548] 'Gardener's Chronicle,' 1852, pp. 435, 691.
+
+[549] Bechstein, 'Naturgesch. Deutschlands,' 1801, B. i. s. 310.
+
+[550] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 224.
+
+[551] G. Lewis's 'Journal of Residence in West Indies,' 'Home and Col.
+Library,' p. 100.
+
+[552] Sidney's edit. of Youatt on the Pig, p.24.
+
+[553] 'Journal of Horticulture,' 1862, pp. 476, 498; 1865, p. 460. With
+respect to the heartsease, 'Gardener's Chronicle,' 1863, p. 628.
+
+[554] 'Des Jacinthes, de leur Culture,' 1768, p. 53: on wheat, 'Gardener's
+Chronicle,' 1846, p. 653.
+
+[555] W. B. Tegetmeier, 'The Field,' Feb. 25, 1865. With respect to black
+fowls, _see_ a quotation in Thompson's 'Nat. Hist. of Ireland,' 1849, vol.
+i. p. 22.
+
+[556] 'Bull. de la Soc. d'Acclimat.,' tom. vii. 1860, p. 359.
+
+[557] 'Transact. Hort. Soc.,' vol. i. 2nd series, 1835, p. 275. For
+raspberries, _see_ 'Gard. Chronicle,' 1855, p. 154, and 1863, p. 245.
+
+[558] 'Gardener's Chronicle,' 1843, p. 806.
+
+[559] Ibid., 1850, p. 732.
+
+[560] Ibid., 1860, p. 956.
+
+[561] J. De Jonghe, in 'Gard. Chronicle,' 1860, p. 120.
+
+[562] Downing, 'Fruit-trees of North America,' pp. 266, 501: in regard to
+the cherry, p. 198.
+
+[563] 'Gardener's Chronicle,' 1849, p. 755.
+
+[564] 'Journal of Horticulture,' Sept. 26th, 1865, p. 254; _see_ other
+references given in chap. x.
+
+[565] Mr. Selby, in 'Mag. of Zoology and Botany,' Edinburgh, vol. ii.,
+1838, p. 393.
+
+[566] The Reine Claude de Bavay, 'Journal of Horticulture,' Dec. 27, 1864,
+p. 511.
+
+[567] Mr. Pusey, in 'Journal of R. Agricult. Soc., vol. vi. p. 179. For
+Swedish turnips, _see_ 'Gard. Chron.,' 1847, p. 91.
+
+[568] Godron, 'De l'Espece,' tom. ii. p. 98.
+
+[569] 'Gardener's Chron.,' 1866, p. 732.
+
+[570] 'Gardener's Chronicle,' 1862, pp. 820, 821.
+
+[571] 'On the Varieties of Wheat,' p. 59.
+
+[572] Mr. Hewitt and others, in 'Journal of Hort.,' 1862, p. 773.
+
+[573] 'Encyclop. of Rural Sports,' p. 405.
+
+[574] Col. Le Couteur, 'Journal Roy. Agricult. Soc.,' vol. iv. p. 43.
+
+[575] 'Gardener's Chronicle,' 1845, p. 273.
+
+[576] 'Journal of Horticulture,' 1862, p. 157.
+
+[577] 'Cottage Gardener,' 1860, p. 368.
+
+[578] 'A Review of Reports,' 1808, p. 406.
+
+[579] 'Gardener's Chronicle,' 1853, p. 45.
+
+[580] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gen.,' tom. iii. p. 49. On
+the Cochineal Insect, p. 46.
+
+[581] Capt. Marryat, quoted by Blyth in 'Journ. Asiatic Soc. of Bengal,'
+vol. xxviii. p. 229.
+
+[582] Mr. Oxley, 'Journal of the Indian Archipelago,' vol. ii., 1848, p.
+645.
+
+[583] Mr. Abbey, in 'Journal of Horticulture,' Dec. 1, 1863, p. 430.
+
+[584] 'On Naval Timber,' 1831, p. 107.
+
+[585] Mr. Baily, in 'The Poultry Chronicle,' vol. ii., 1854, p. 150. Also
+vol. i. p. 342; vol. iii. p. 245.
+
+[586] 'Cottage Gardener,' 1855, December, p. 171; 1856, January, pp. 248,
+323.
+
+[587] 'Ueber Shorthorn Rindvieh,' 1857, s. 51.
+
+[588] 'The Veterinary,' vol. xiii. p. 720. For the Glamorganshire cattle,
+_see_ Youatt on Cattle, p. 51.
+
+[589] J. M. Eaton, 'A Treatise on Fancy Pigeons,' p. 82; Ferguson, on 'Rare
+and Prize Poultry,' p. 162; Mr. Brent, in 'Cottage Gardener,' Oct. 1860. p.
+13.
+
+[590] 'Die Racen des Schweines,' 1860, s. 48.
+
+[591] _See_ some good remarks on this head by M. de Quatrefages, 'Unite de
+l'Espece Humaine,' 1861, p. 119.
+
+[592] Verlot, 'Des Varietes,' 1865, p. 94.
+
+[593] Mr. Patrick Sheriff, in 'Gard. Chronicle,' 1858, p. 771.
+
+[594] 'Pomologie Physiolog.,' 1830, p. 106.
+
+[595] Youatt on Sheep, p. 521.
+
+[596] 'A Treatise on the Almond Tumbler,' p. i.
+
+[597] M. J. de Jonghe, in 'Gard. Chron.,' 1858, p. 173.
+
+[598] Max. Mueller, 'Science of Language,' 1861, p. 223.
+
+[599] Youatt on Cattle, pp. 116, 128.
+
+[600] 'Domesticated Animals,' p. 188.
+
+[601] Volz, 'Beitraege zur Kulturgeschichte,' 1852, s. 99 _et passim_.
+
+[602] Blaine, 'Encyclop. of Rural Sports,' p. 213.
+
+[603] 'Des Jacinthes,' &c., Amsterdam, 1768, p. 43; Verlot, 'Des Varietes,'
+&c., p. 86. On the reindeer, _see_ Linnaeus, 'Tour in Lapland,' translated
+by Sir J. E. Smith, vol. i. p. 314. The statement in regard to German
+shepherds is given on the authority of Dr. Weinland.
+
+[604] Mueller's 'Physiology,' Eng. translation, vol. ii. p. 1662. With
+respect to the similarity of twins in constitution, Dr. William Ogle has
+given me the following extract from Professor Trousseau's Lectures
+('Clinique Medicale,' tom. i. p. 523), in which a curious case is
+recorded:--"J'ai donne mes soins a deux freres jumeaux, tous deux si
+extraordinairement ressemblants qu'il m'etait impossible de les
+reconnaitre, a moins de les voir l'un a cote de l'autre. Cette ressemblance
+physique s'etendait plus loin: ils avaient, permettez-moi l'expression, une
+similitude pathologique plus remarquable encore. Ainsi l'un d'eux que je
+voyais aux neothermes a Paris malade d'une ophthalmie rhumatismale me
+disait, 'En ce moment mon frere doit avoir une ophthalmie comme la mienne;'
+et comme je m'etais recrie, il me montrait quelques jours apres une lettre
+qu'il venait de recevoir de ce frere alors a Vienne, et qui lui ecrivait en
+effet--'J'ai mon ophthalmie, tu dois avoir la tienne.' Quelque singulier
+que ceci puisse paraitre, le fait non est pas moins exact: on ne me l'a pas
+raconte, je l'ai vu, et j'en ai vu d'autres analogues dans ma pratique. Ces
+deux jumeaux etaient aussi tous deux asthmatiques, et asthmatiques a un
+effroyable degre. Originaires de Marseille, ils n'ont jamais pu demeurer
+dans cette ville, ou leurs interets les appelaient souvent, sans etre pris
+de leurs acces; jamais ils n'en eprouvaient a Paris. Bien mieux, il leur
+suffisait de gagner Toulon pour etre gueris de leurs attaques de
+Marseilles. Voyageant sans cesse et dans tous pays pour leurs affaires, ils
+avaient remarque que certaines localites leur etaient funestes, que dans
+d'autres ils etaient exempts de tout phenomene d'oppression."
+
+[605] Isid. Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. iii. p. 352;
+Moquin Tandon, 'Teratologie Vegetale,' 1841, p. 115.
+
+[606] Metzger, 'Die Getreidearten,' 1841, s. 39.
+
+[607] On the date-palm, _see_ Vogel, 'Annals and Mag. of Nat. Hist.,' 1854,
+p. 460. On Indian varieties, Dr. F. Hamilton, 'Transact. Linn. Soc.,' vol.
+xiv. p. 296. On the varieties cultivated in Tahiti, _see_ Dr. Bennett, in
+Loudon's 'Mag. of N. Hist.,' vol. v., 1832, p. 484. Also Ellis, 'Polynesian
+Researches,' vol. i. pp. 375, 370. On twenty varieties of the Pandanus and
+other trees in the Marianne Island, _see_ 'Hooker's Miscellany,' vol. i. p.
+308. On the bamboo in China, _see_ Huc's 'Chinese Empire,' vol. ii. p. 307.
+
+[608] 'Treatise on the Culture of the Apple,' &c., p. 3.
+
+[609] Gallesio, 'Teoria della Riproduzione Veg.,' p. 125.
+
+[610] _See_ Dr. Hooker's Memoir on Arctic Plants in 'Linn. Transact.,' vol.
+xxiii, part ii. Mr. Woodward, and a higher authority cannot be quoted,
+speaks of the Arctic mollusca (in his 'Rudimentary Treatise,' 1856, p. 355)
+as remarkably subject to variation.
+
+[611] Bechstein, in his 'Naturgeschichte der Stubenvoegel,' 1840, s. 238,
+has some good remarks on this subject. He states that his canary-birds
+varied in colour, though kept on uniform food.
+
+[612] 'The Plant,' by Schleiden, translated by Henfrey, 1848, p. 169. _See_
+also Alex. Braun, in 'Bot. Memoirs,' Ray. Soc., 1853, p. 313.
+
+[613] Messrs. Hardy and Son, of Maldon, in 'Gard. Chronicle,' 1856, p. 458.
+
+[614] 'Quadrupedes du Paraguay,' 1801, tom. ii. p. 319.
+
+[615] McClelland on Indian Cyprinidae, 'Asiatic Researches,' vol. xix. part
+ii., 1839, pp. 266, 268, 313.
+
+[616] Quoted by Sageret, 'Pom. Phys.,' 1830, p. 43.
+
+[617] 'The Fruits of America,' 1845, p. 5.
+
+[618] M. Cardan, in 'Comptes Rendus,' Dec. 1848, quoted in 'Gard.
+Chronicle,' 1849, p. 101.
+
+[619] M. Alexis Jordan mentions four excellent pears found in woods in
+France, and alludes to others ('Mem. Acad. de Lyon,' tom. ii. 1852, p.
+159). Poiteau's remark is quoted in 'Gardener's Mag.,' vol. iv., 1828, p.
+385. _See_ 'Gard. Chronicle,' 1862, p. 335, for another case of a new
+variety of the pear found in a hedge in France. Also for another case,
+_see_ Loudon's 'Encyclop. of Gardening,' p. 901. Mr. Rivers has given me
+similar information.
+
+[620] Duval, 'Hist. du Poirier,' 1849, p. 2.
+
+[621] I infer that this is the fact from Van Mons' statement ('Arbres
+Fruitiers,' 1835, tom. i. p. 446) that he finds in the woods seedlings
+resembling all the chief cultivated races of both the pear and apple. Van
+Mons, however, looked at these wild varieties as aboriginal species.
+
+[622] Downing, 'Fruit-trees of North America,' p. 422; Foley, in 'Transact.
+Hort. Soc.,' vol. vi. p. 412.
+
+[623] 'Gard. Chronicle,' 1847, p. 244.
+
+[624] 'Gardener's Chronicle,' 1841, p. 383; 1850, p. 700; 1854, p. 650.
+
+[625] 'Die Getreidearten,' 1843, s. 66, 116, 117.
+
+[626] Sabine, in 'Hort. Transact.,' vol. iii. p. 225; Bronn, 'Geschichte
+der Natur,' b. ii. s. 119.
+
+[627] 'Journal of Horticulture,' 1861, p. 112; on Zinnia, 'Gardener's
+Chronicle,' 1860, p. 852.
+
+[628] 'The Chrysanthemum, its History, &c.,' 1865, p. 3.
+
+[629] 'Gardener's Chron.,' 1855, p. 54; 'Journal of Horticulture,' May 9,
+1865, p. 363.
+
+[630] Quoted by Verlot, 'Des Varietes,' &c., 1865, p. 28.
+
+[631] 'Examination of the Characteristics of Genera and Species:'
+Charleston, 1855, p. 14.
+
+[632] Mr Hewitt, 'Journal of Hort.,' 1863, p. 39.
+
+[633] Devay, 'Mariages Consanguins,' pp. 97, 125. In conversation I have
+found two or three naturalists of the same opinion.
+
+[634] Mueller has conclusively argued against this belief, 'Elements of
+Phys.,' Eng. translat., vol. ii., 1842, p. 1405.
+
+[635] 'Act. Acad. St. Petersburg,' 1780, part ii. p. 84, &c.
+
+[636] 'Bastarderzeugung,' s. 249, 255, 295.
+
+[637] 'Nova Acta, St. Petersburg,' 1794, p. 378; 1795, pp. 307, 313, 316;
+1787, p. 407.
+
+[638] 'De la Fecondation,' 1862, p. 311.
+
+[639] 'Amaryllidaceae,' 1837, p. 362.
+
+[640] Abstracted in 'Gard. Chronicle,' 1860, p. 1081.
+
+[641] This was the opinion of the elder De Candolle, as quoted in 'Dic.
+Class. d'Hist. Nat.,' tom. viii. p. 405. Puvis, in his work, 'De la
+Degeneration,' 1837, p. 37, has discussed this same point.
+
+[642] 'Comptes Rendus,' Novembre 21, 1864, p. 838.
+
+[643] 'Nova Acta, St. Petersburg,' 1794, p. 391.
+
+[644] 'Bastarderzeugung,' s. 507, 516, 572.
+
+[645] 'Die Bastardbefruchtung,' &c., 1865, s. 24.
+
+[646] 'Bastarderzeugung,' s. 452, 507.
+
+[647] 'Die Bastardbefruchtung,' s. 56.
+
+[648] 'Bastarderzeugung,' s. 423.
+
+[649] 'Dritte Fortsetzung,' &c., 1766, s. 85.
+
+[650] 'Die Bastardbefruchtung,' &c., 1865, s. 92; _see_ also the Rev. M. J.
+Berkeley on the same subject, in 'Journal of Royal Hort. Soc.,' 1866, p.
+80.
+
+[651] Dr. P. Lucas has given a history of opinion on this subject: 'Hered.
+Nat.,' 1847, tom. i. p. 175.
+
+[652] 'Hist. des Anomalies,' tom. iii. p. 499.
+
+[653] Idem., tom. iii. pp. 392, 502.
+
+[654] _See_ his interesting work, 'Metamorphoses de l'Homme,' &c., 1862, p.
+129.
+
+[655] 'Dritte Fortsetzung,' &c., s. 123; 'Bastarderzeugung,' s. 249.
+
+[656] 'Gardener's Chronicle,' 1853, p. 183.
+
+[657] Mr. Wildman, 'Floricultural Soc.,' Feb. 7, 1843, reported in 'Gard.
+Chron.,' 1843, p. 86.
+
+[658] Mr. Robson, in 'Journal of Horticulture,' Feb. 13th, 1866, p. 122.
+
+[659] 'Journal of Horticulture,' 1861, p. 24.
+
+[660] Ibid., 1862, p. 83.
+
+[661] 'Gard. Chron.,' 1845, p. 660.
+
+[662] Ibid., 1863, p. 628.
+
+[663] 'Journal of Hort.,' 1861, pp. 64, 309.
+
+[664] 'Des Varietes,' &c., p. 76.
+
+[665] Engel, 'Sur les Prop. Medicales des Plantes,' 1860, pp. 10, 25. On
+changes in the odours of plants, _see_ Dalibert's Experiments, quoted by
+Beckman, 'Inventions,' vol. ii. p. 344; and Nees, in Ferussac, 'Bull. des
+Sc. Nat.,' 1824, tom. i. p. 60. With respect to the rhubarb, &c., _see_
+also 'Gardener's Chronicle,' 1849, p. 355; 1862, p. 1123.
+
+[666] Hooker, 'Flora Indica,' p. 32.
+
+[667] Naudin, 'Annales des Sc. Nat.,' 4th series, Bot., tom. xi., 1859, p.
+81. 'Gardener's Chronicle,' 1859, p. 464.
+
+[668] Moorcroft's 'Travels,' &c., vol. ii. p. 143.
+
+[669] 'Gardener's Chronicle,' 1861, p. 1113.
+
+[670] Royle, 'Productive Resources of India,' p. 59.
+
+[671] 'Personal Narrative,' Eng. translat., vol. v. p. 101. This statement
+has been confirmed by Karsten ('Beitrag zur Kenntniss der Rhynchoprion:'
+Moscow, 1864. s. 39), and by others.
+
+[672] 'Organic Chemistry,' Eng. translat., 1st edit., p. 369.
+
+[673] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 155.
+
+[674] Darwin, 'Journal of Researches,' 1845, p. 434.
+
+[675] These statements on disease are taken from Dr. Boudin's 'Geographie
+et de Statistique Medicales,' 1857, tom. i. p. xliv. and lii.; tom. ii. p.
+315.
+
+[676] E. Desor, quoted in the 'Anthrop. Rev.,' 1863, p. 180. For much
+confirmatory evidence, _see_ Quatrefages, 'Unite de l'Espece Humaine,'
+1861, p. 131.
+
+[677] 'Ceylon,' by Sir J. E. Tennent, vol. i., 1859, p. 89.
+
+[678] Godron, 'De l'Espece,' tom. ii. p. 52.
+
+[679] 'Journal of Horticultural Soc.,' vol. vii., 1852, p. 117.
+
+[680] 'Journal of Hort. Soc.,' vol. i. p. 160.
+
+[681] _See_ Lecoq on the Villosity of Plants, 'Geograph. Bot.,' tom. iii.
+pp. 287, 291; Gaertner, 'Bastarderz.,' s. 261; Mr. Musters, on the Opuntia,
+in 'Gard. Chronicle,' 1846, p. 444.
+
+[682] 'Pom. Phys.,' p. 136.
+
+[683] 'Ampelographie,' 1849, p. 19.
+
+[684] Gaertner, 'Bastarderz.,' s. 606, has collected nearly all recorded
+facts. Andrew Knight (in 'Transact. Hort. Soc.,' vol. ii. p. 160) goes so
+far as to maintain that few varieties are absolutely permanent in character
+when propagated by buds or grafts.
+
+[685] Mr. Blyth, in 'Annals and Mag. of Nat. Hist.,' vol. xx., 1847, p.
+391.
+
+[686] 'Natural History Review,' 1862, p. 113.
+
+[687] 'Journal of Roy. Geographical Soc.,' vol. ix., 1839, p. 275.
+
+[688] 'Travels in Bokhara,' vol. iii. p. 151.
+
+[689] _See_ also, on the influence of marshy pastures on the wool, Godron,
+'L'Espece,' tom. ii. p. 22.
+
+[690] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gen.,' tom. iii. p. 438.
+
+[691] Azara has made some good remarks on this subject, 'Quadrupedes du
+Paraguay,' tom. ii. p. 337. _See_ an account of a family of naked mice
+produced in England, 'Proc. Zoolog.  Soc.,' 1856, p. 38.
+
+[692] 'Die Fauna der Pfahlbauten,' 1861, s. 15.
+
+[693] 'Schweinschaedel,' 1864, s. 99.
+
+[694] 'Travels in Siberia,' Eng. translat., vol. i. p. 228.
+
+[695] A. R. Wallace, 'Travels on the Amazon and Rio Negro,' p. 294.
+
+[696] 'Naturgeschichte der Stubenvoegel,' 1840, s. 262, 308.
+
+[697] 'Hist. Nat. Gen.,' tom. iii. p. 402.
+
+[698] 'Bull. de la Soc. Imp. d'Acclimat.,' tom. viii. p. 351.
+
+[699] _See_ an account of Mr. Gregson's experiments on the _Abraxus
+grossulariata_, 'Proc. Entomolog. Soc.,' Jan. 6th, 1862: these experiments
+have been confirmed by Mr. Greening, in 'Proc. of the Northern Entomolog.
+Soc.,' July 28th, 1862. For the effects of food on caterpillars, see a
+curious account by M. Michely, in 'Bull. de la Soc. Imp. d'Acclimat.,' tom.
+viii. p. 563. For analogous facts from Dahlbom on Hymenoptera, _see_
+Westwood's 'Modern Class. of Insects,' vol. ii. p. 98. _See_ also Dr. L.
+Moeller, 'Die Abhaengigkeit der Insecten,' 1867, s. 70.
+
+[700] 'The Principles of Biology,' vol. ii. 1866. The present chapters were
+written before I had read Mr. Herbert Spencer's work, so that I have not
+been able to make so much use of it as I should otherwise probably have
+done.
+
+[701] 'Proc. Acad. Nat. Soc. of Philadelphia,' Jan. 28th, 1862.
+
+[702] _See_ Mr. B. D. Walsh's excellent papers in 'Proc. Entomolog. Soc.
+Philadelphia,' Dec. 1866, p. 284. With respect to the willow, _see_ idem,
+1864, p. 546.
+
+[703] _See_ his admirable Histoire des Galles, in 'Annal. des Sc. Nat.
+Bot.,' 3rd series, tom. xix., 1853, p. 273.
+
+[704] Kirby and Spence's 'Entomology,' 1818, vol. i. p. 450;
+Lucaze-Duthiers, idem, p. 284.
+
+[705] 'Proc. Entomolog. Soc. Philadelphia,' 1864, p. 558.
+
+[706] Mr. B. D. Walsh, idem, p. 633; and Dec. 1866, p. 275.
+
+[707] Mr. B. D. Walsh, idem, 1864, p. 545, 411, 495; and Dec. 1866, p. 278.
+_See_ also Lucaze-Duthiers.
+
+[708] Lucaze-Duthiers, idem, pp. 325, 328.
+
+[709] 'Linnaea,' vol. xvii., 1843; quoted by Dr. M. T. Masters, Royal
+Institution, March 16th, 1860.
+
+[710] Hewett C. Watson, 'Cybele Britannica,' vol. i., 1847, p. 11.
+
+[711] 'Gardener's Chronicle,' 1857, p. 629.
+
+[712] 'Memoire sur la Production Artificielle des Monstrosites,' 1862, pp.
+8-12; 'Recherches sur les Conditions, &c., chez les Monstres,' 1863, p. 6.
+An abstract is given of Geoffroy's Experiments by his son, in his 'Vie,
+Travaux, &c.,' 1847, p. 290.
+
+[713] Paget, 'Lectures on Surgical Pathology,' 1853, vol. i. p. 483.
+
+[714] 'Researches upon the Venom of the Rattle-snake,' Jan. 1861, by Dr.
+Mitchell, p. 67.
+
+[715] Mr. Sedgwick, in 'British and Foreign Medico-Chirurg. Review,' July
+1863, p. 175.
+
+[716] 'An Essay on Generation,' Eng. translat., p. 18; Paget, 'Lectures on
+Surgical Pathology,' 1853, vol. i. p. 209.
+
+[717] 'An Essay on Animal Reproduction,' Eng. translat., 1769, p. 79.
+
+[718] Carpenter's 'Principles of Comp. Physiology,' 1854, p. 479.
+
+[719] Charlesworth's 'Mag. of Nat. Hist.,' vol. i., 1837, p. 145.
+
+[720] Paget, 'Lectures on Surgical Pathology,' vol. i. p. 239.
+
+[721] Quoted by Carpenter, 'Comp. Phys.,' p. 479.
+
+[722] Paget, 'Lectures,' &c., p. 257.
+
+[723] These cases are given by Blumenbach in his 'Essay on Generation,' pp.
+52, 54.
+
+[724] 'Cellular Pathology,' trans. by Dr. Chance, 1860, pp. 27, 441.
+
+[725] Paget, 'Lectures on Pathology,' vol. i., 1853, p. 357.
+
+[726] Paget, idem, p. 150.
+
+[727] 'The Principles of Biology,' vol. ii., 1866, chap. 3-5.
+
+[728] 'Lectures on Pathology,' 1853, vol. i. p. 71.
+
+[729] 'Comptes Rendus,' Sept. 26th, 1864, p. 539.
+
+[730] 'The Principles of Biology,' vol. ii. p. 243.
+
+[731] Idem, vol. ii. p. 269.
+
+[732] Idem, vol. ii. p. 273.
+
+[733] Paget, 'Lectures on Pathology,' vol. ii. p. 209.
+
+[734] Mueller's 'Phys.,' Eng. translat., pp. 54, 791. Prof. Reed has given
+('Physiological and Anat. Researches,' p. 10) a curious account of the
+atrophy of the limbs of rabbits after the destruction of the nerve.
+
+[735] Quoted by Lecoq, in 'Geograph. Bot.,' tom. i., 1854, p. 182.
+
+[736] 'Das Abaendern der Voegel,' 1833, s. 74.
+
+[737] Nathusius, 'Die Racen des Schweines,' 1860, s. 53, 57; 'Vorstudien
+... Schweineschaedel,' 1864, s. 103, 130, 133.
+
+[738] 'Journal of Agriculture of Highland Soc.,' July, 1860, p. 321.
+
+[739] 'Principles of Biology,' vol. ii. p. 263.
+
+[740] 'Natural History Review,' vol. iv., Oct. 1864, p. 617.
+
+[741] 'Lectures on Surgical Pathology,' 1853, vol. i. p. 27.
+
+[742] Andersson, 'Travels in South Africa,' p. 318. For analogous cases in
+South America, _see_ Aug. St. Hilaire, 'Voyage dans le Province de Goyaz,'
+tom. i. p. 71.
+
+[743] Brickell's 'Nat. Hist. of North Carolina,' 1739, p. 53.
+
+[744] Livingstone, quoted by Youatt on Sheep, p. 142. Hodgson, in 'Journal
+of Asiatic Soc. of Bengal,' vol. xvi., 1847, p. 1006, &c. &c.
+
+[745] 'Naturalist Library,' Dogs, vol. ii. 1840, p. 104.
+
+[746] 'De l'Espece,' tom. i., 1859, p. 367.
+
+[747] 'Ceylon,' by Sir J. E. Tennent, 1859, vol. ii. p. 531.
+
+[748] For the foregoing statements, _see_ Hunter's 'Essays and
+Observations,' 1861, vol. ii. p. 329; Dr. Edmondston, as quoted in
+Macgillivray's 'British Birds,' vol. v. p. 550; Menetries, as quoted in
+Bronn's 'Geschichte der Natur,' B. ii. s. 110.
+
+[749] These statements on the intestines are taken from Isidore Geoffroy
+St. Hilaire, 'Hist. Nat. Gen.,' tom. iii. pp. 427, 441.
+
+[750] Gilbert White, 'Nat. Hist. Selbourne,' 1825, vol. ii. p. 121.
+
+[751] Burdach, 'Traite de Phys.,' tom. ii. p. 267, as quoted by Dr. P.
+Lucas, 'L'Hered. Nat.,' tom. i. p. 388.
+
+[752] This and several other cases are given by Colin, 'Physiologie Comp.
+des Animaux Dom.,' 1854, tom. i. p. 426.
+
+[753] M. Michely de Cayenne, in 'Bull. Soc. d'Acclimat.,' tom. viii., 1861,
+p. 563.
+
+[754] Quatrefages, 'Unite de l'Espece Humaine,' 1861, p. 79.
+
+[755] 'Flora,' 1835, B. ii. p. 504.
+
+[756] Alph. De Candolle, 'Geograph. Bot.,' tom. ii. p. 1078.
+
+[757] Royle, 'Illustrations of the Botany of the Himalaya,' p. 19.
+
+[758] 'Gardener's Chronicle,' 1850, pp. 204, 219.
+
+[759] Rev. R. Everest, 'Journal As. Soc. of Bengal,' vol. iii. p. 19.
+
+[760] Youatt on Sheep, 1838, p. 491.
+
+[761] Royle, 'Prod. Resources of India,' p. 153.
+
+[762] Tegetmeier, 'Poultry Book,' 1866, p. 102.
+
+[763] Dr. R. Paterson, in a paper communicated to Bot. Soc. of Canada,
+quoted in the 'Reader,' 1863. Nov. 13th.
+
+[764] _See_ remarks by Editor in 'Gard. Chronicle,' 1848, p. 5.
+
+[765] 'Gard. Chronicle,' 1860, p. 938. Remarks by Editor and quotation from
+Decaisne.
+
+[766] J. de Jonghe, of Brussels, in 'Gard. Chronicle,' 1857, p. 612.
+
+[767] Ch. Martius, 'Voyage Bot. Cotes Sept. de la Norvege,' p. 26.
+
+[768] 'Journal de l'Acad. Hort. de Gand,' quoted in 'Gard. Chron.,' 1859,
+p. 7.
+
+[769] 'Gard. Chronicle,' 1851, p. 396.
+
+[770] Idem., 1862, p. 235.
+
+[771] On the authority of Labat, quoted in 'Gard. Chron.,' 1862, p. 235.
+
+[772] MM. Edwards and Colin, 'Annal. des Sc. Nat.,' 2nd series, Bot., tom.
+v. p. 22.
+
+[773] 'Geograph. Bot.,' p. 337.
+
+[774] 'Swedish Acts,' Eng. translat., 1739-40, vol. i. Kalm, in his
+'Travels,' vol. ii. p. 166, gives an analogous case with cotton-plants
+raised in New Jersey from Carolina seed.
+
+[775] De Candolle, 'Geograph. Bot.,' p. 339.
+
+[776] 'Gard. Chronicle,' 1862, p. 235.
+
+[777] Gallesio, 'Teoria della Riproduzione Veg.,' 1816, p. 125; and 'Traite
+du Citrus,' 1811, p. 359.
+
+[778] 'Essai sur l'Hist. des Orangers,' 1813, p. 20, &c.
+
+[779] Alph. De Candolle, 'Geograph. Bot.,' p. 882.
+
+[780] 'Ch. Darwin's Lehre von der Entstehung,' &c., 1862, s. 87.
+
+[781] Decaisne, quoted in 'Gard. Chronicle,' 1865, p. 271.
+
+[782] For the magnolia, _see_ Loudon's 'Gard. Mag.,' vol. xiii., 1837, p.
+21. For camellias and roses, _see_ 'Gard. Chron.,' 1860, p. 384. For the
+yew, 'Journal of Hort.,' March 3rd, 1863, p. 174. For sweet potatoes, _see_
+Col. von Siebold, in 'Gard. Chron.,' 1855, p. 822.
+
+[783] The Editor, 'Gard. Chron.,' 1861, p. 239.
+
+[784] Loudon's 'Gard. Mag.,' vol. xii., 1836, p. 378.
+
+[785] 'Gardeners Chron.,' 1865, p. 699.
+
+[786] 'Arboretum et Fruticetum,' vol. iii. p. 1376.
+
+[787] Mr. Robson, in 'Journal of Horticulture,' 1861, p. 23.
+
+[788] Dr. Bonavia, 'Report of the Agri.-Hort. Soc. of Oudh,' 1866.
+
+[789] 'Cottage Gardener,' 1860, April, 24th, p. 57.
+
+[790] 'Gardener's Chronicle,' 1841, p. 291.
+
+[791] Mr. Beaton, in 'Cottage Gardener,' March 20th, 1860, p. 377. Queen
+Mab will also stand stove heat, _see_ 'Gard. Chronicle,' 1845, p. 226.
+
+[792] 'Gardener's Chronicle,' 1841, p. 439.
+
+[793] Quoted by Asa Gray, in 'Am. Journ. of Sci.,' 2nd series, Jan. 1865,
+p. 106.
+
+[794] For China, _see_ 'Memoire sur les Chinois,' tom, xi., 1786, p. 60.
+Columella is quoted by Carlier, in 'Journal de Physique,' tom. xxiv. 1784.
+
+[795] Messrs. Hardy and Son, in 'Gard. Chronicle,' 1856, p. 589.
+
+[796] Isid. Geoffroy St. Hilaire, 'Hist. Nat. des Anomalies,' 1836, tom.
+ii. pp. 210, 223, 224, 395; 'Philosoph. Transact.,' 1775, p. 313.
+
+[797] Pallas, quoted by Youatt on Sheep, p. 25.
+
+[798] Youatt on Cattle, 1834, p. 174.
+
+[799] 'Encyclop. Method.,' 1820, p. 483: _see_ p. 500, on the Indian zebu
+casting its horns. Similar cases in European cattle were given in the third
+chapter.
+
+[800] Pallas, 'Travels,' Eng. translat., vol. i. p. 243.
+
+[801] Mr. Beaton, in 'Journal of Horticulture,' May 21, 1861, p. 133.
+
+[802] Lecoq, 'De la Fecondation,' 1862, p. 233.
+
+[803] 'Annales du Museum,' tom. vi. p. 319.
+
+[804] 'Hist. des Anomalies,' tom. iii. p. 392. Prof. Huxley applies the
+same principle in accounting for the remarkable, though normal, differences
+in the arrangement of the nervous system in the Mollusca, in his great
+paper on the Morphology of the Cephalous Mollusca, in 'Phil. Transact.,'
+1853, p. 56.
+
+[805] 'Elements de Teratologie Veg.,' 1841, p. 113.
+
+[806] Prof. J. B. Simonds, on the Age of the Ox, Sheep, &c., quoted in
+'Gard. Chronicle,' 1854, p. 588.
+
+[807] 'Hist. des Anomalies,' tom. i. p. 674.
+
+[808] Quoted by Isid. Geoffroy, idem, tom. i. p. 635.
+
+[809] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 250.
+
+[810] A. Walker on Intermarriage, 1838, p. 160.
+
+[811] 'The Farrier and Naturalist,' vol. i., 1828, p. 456.
+
+[812] Godron, 'Sur l'Espece,' tom. ii. p. 217.
+
+[813] 'Quadrupedes du Paraguay,' tom. ii. p. 333.
+
+[814] On Sheep, p. 142.
+
+[815] 'Ueber Racen, Kreuzungen, &c.,' 1825, s. 24.
+
+[816] Quoted from Conolly, in 'The Indian Field,' Feb. 1859, vol. ii. p.
+266.
+
+[817] 'Domesticated Animals of the British Islands,' pp. 307, 368.
+
+[818] 'Proceedings Zoolog. Soc.,' 1833, p. 113.
+
+[819] Sedgwick, 'Brit. and Foreign Medico-Chirurg. Review,' April 1863, p.
+453.
+
+[820] 'Gard. Chronicle,' 1849, p. 205.
+
+[821] 'Embassy to the Court of Ava,' vol. i. p. 320.
+
+[822] 'Narrative of a Mission to the Court of Ava in 1855,' p. 94.
+
+[823] Those statements are taken from Mr. Sedgwick, in the 'Medico-Chirurg.
+Review,' July 1861, p. 198; April 1863, pp. 455 and 458. Liebreich is
+quoted by Professor Devay, in his 'Mariages Consanguins,' 1862, p. 116.
+
+[824] Loudon's 'Mag. of Nat. Hist.,' vol. i., 1829, pp. 66, 178. _See_ also
+Dr. P. Lucas, 'L'Hered. Nat.,' tom. i. p. 428, on the inheritance of
+deafness in cats.
+
+[825] 'Annales des Sc. Nat.' Zoolog., 3rd series, 1847, tom. viii. p. 239.
+
+[826] 'Gardener's Chron.,' 1864, p. 1202.
+
+[827] Verlot gives several other instances, 'Des Varietes,' 1865, p. 72.
+
+[828] 'Arbres Fruitiers,' 1836, tom. ii. pp. 204, 226.
+
+[829] 'Annales du Museum,' tom. xx. p. 188.
+
+[830] 'Gardener's Chron.,' 1843, p. 877.
+
+[831] Ibid., 1845, p. 102.
+
+[832] 'Hist. des Anomalies,' tom. iii. p. 402. _See_ also M. Camille
+Dareste, 'Recherches sur les Conditions,' &c., 1863, pp. 16, 48.
+
+[833] Rev. E. S. Dixon, 'Ornamental Poultry,' 1848, p. 111; Isidore
+Geoffroy, 'Hist. Anomalies,' tom. i. p. 211.
+
+[834] 'On the Breeding of Domestic Animals,' 1829, p. 6.
+
+[835] Youatt on Cattle, 1834, p. 283.
+
+[836] Mr. Herbert Spencer ('Principles of Biology,' 1864, vol. i. pp. 452,
+468) takes a different view; and in one place remarks: "We have seen reason
+to think that, as fast as essential faculties multiply, and as fast as the
+number of organs that co-operate in any given function increases, indirect
+equilibration through natural selection becomes less and less capable of
+producing specific adaptations; and remains fully capable only of
+maintaining the general fitness of constitution to conditions." This view
+that natural selection can do little in modifying the higher animals
+surprises me, seeing that man's selection has undoubtedly effected much
+with our domesticated quadrupeds and birds.
+
+[837] Dr. Prosper Lucas apparently disbelieves in any such connexion,
+'L'Hered. Nat.,' tom. ii. pp. 88-94.
+
+[838] 'British Medical Journal,' 1862, p. 433.
+
+[839] Boudin, 'Geograph. Medicale,' tom. i. p. 406.
+
+[840] This fact and the following cases, when not stated to the contrary,
+are taken from a very curious paper by Prof. Heusinger, in 'Wochenschrift
+fuer Heilkunde,' May 1846, s. 277.
+
+[841] Mr. Mogford, in the 'Veterinarian,' quoted in 'The Field,' Jan. 22,
+1861, p. 545.
+
+[842] 'Edinburgh Veterinary Journal,' Oct. 1860, p. 347.
+
+[843] 'Hist. des Anomalies,' 1832, tom. i. pp. 22, 537-556; tom. iii. p.
+462.
+
+[844] 'Comptes Rendus,' 1855, pp. 855, 1029.
+
+[845] Carpenter's 'Comp. Phys.,' 1854, p. 480; _see_ also Camille Dareste,
+'Comptes Rendus,' March 20th, 1865, p. 562.
+
+[846] 'Elements of Physiology,' Eng. translat, vol. i., 1838, p. 412. With
+respect to Vrolik, _see_ Todd's 'Cyclop. of Anat. and Phys.,' vol. iv.,
+1849-52, p. 973.
+
+[847] 'Teratologie Veg.,' 1841, livre iii.
+
+[848] 'Hist. des Anomalies,' tom. iii. pp. 4, 5, 6.
+
+[849] 'Teratologie Veg.,' p. 156. _See_ also my paper on climbing plants in
+'Journal of Linn. Soc. Bot.,' vol. ix., 1865, p. 114.
+
+[850] 'Memoires du Museum,' &c., tom. viii. p. 178.
+
+[851] Loudon's 'Encyclop. of Gardening,' p. 829.
+
+[852] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 324.
+
+[853] 'Annales des Sc. Nat.,' 1st series, tom. xix. p. 327.
+
+[854] 'Comptes Rendus,' Dec. 1864, p. 1039.
+
+[855] Ueber Foetale Rachites, 'Wuerzburger Medicin. Zeitschrift,' 1860, B.
+i. s. 265.
+
+[856] 'Teratologie Veg.,' p. 192. Dr. M. Masters informs me that he doubts
+the truth of this conclusion; but the facts to be given seem to be
+sufficient to establish it.
+
+[857] 'Journal of Horticulture,' July 2nd, 1861, p. 253.
+
+[858] It would be worth trial to fertilise with the same pollen the central
+and lateral flowers of the pelargonium, and of some other highly cultivated
+plants, protecting them of course from insects: then to sow the seed
+separately, and observe whether the one or the other lot of seedlings
+varied the most.
+
+[859] Quoted in 'Journal of Horticulture,' Feb. 24, 1863, p. 152.
+
+[860] 'Gardener's Chronicle,' 1866, p. 612. For the Phalaenopsis, _see_
+idem, 1867, p. 211.
+
+[861] Memoires ... des Vegetaux,' 1837, tom. ii. p. 170.
+
+[862] 'Journal of Horticulture,' July 23, 1861, p. 311.
+
+[863] 'Nouvelles Archives du Museum,' tom. i. p. 137.
+
+[864] Hugo von Mohl, 'The Vegetable Cell,' Eng. tr., 1852, p. 76.
+
+[865] The Rev. H. H. Dombrain, in 'Journal of Horticulture,' 1861, June
+4th, p. 174; and June 25th, p. 234; 1862, April 29th, p. 83.
+
+[866] 'Transact. Linn. Soc.,' vol. xxiii., 1861, p. 360.
+
+[867] 'Die Getreidearten,' 1843, s. 208, 209.
+
+[868] 'Gardener's Chronicle,' 1850, p. 198.
+
+[869] Quoted in 'Gardener's Chron.,' 1866, p. 74.
+
+[870] 'Ueber den Begriff der Pflanzenart,' 1834, s. 14.
+
+[871] 'Domesticated Animals,' 1845, p. 351.
+
+[872] Bechstein, 'Naturgeschichte Deutschlands,' Band iv., 1795, s. 31.
+
+[873] 'Proc. Entomolog. Soc. of Philadelphia,' Oct. 1863, p. 213.
+
+[874] Quoted by Paget, 'Lectures on Pathology,' 1853, p. 159.
+
+[875] Dr. Lachmann, also, observes ('Annals and Mag. of Nat. History,' 2nd
+series, vol. xix., 1857, p. 231) with respect to infusoria, that "fissation
+and gemmation pass into each other almost imperceptibly." Again, Mr. W. C.
+Minor ('Annals and Mag. of Nat. Hist.,' 3rd series, vol. xi. p. 328) shows
+that with Annelids the distinction that has been made between fission and
+budding is not a fundamental one. _See_ Bonnet, 'Oeuvres d'Hist. Nat.,'
+tom. v., 1781, p. 339, for remarks on the budding-out of the amputated
+limbs of Salamanders. _See_, also, Professor Clark's work 'Mind in Nature,'
+New York, 1865, pp. 62, 94.
+
+[876] Paget, 'Lectures on Pathology,' 1853, p. 158.
+
+[877] Idem, pp. 152, 164.
+
+[878] On the Asexual Reproduction of Cecydomyide Larvae, translated in
+'Annals and Mag. of Nat. Hist.,' March 1866, pp. 167, 171.
+
+[879] _See_ some excellent remarks on this head by Quatrefages, in 'Annales
+des Sc. Nat.,' Zoolog., 3rd series, 1850, p. 138.
+
+[880] 'Annals and Mag. of Nat. Hist.,' 2nd series, vol. xx., 1857, pp.
+153-455.
+
+[881] 'Annales des Sc. Nat.,' 3rd series, 1850, tom. xiii.
+
+[882] 'Transact. Phil. Soc.,' 1851, pp. 196, 208, 210; 1853, p. 245, 247.
+
+[883] 'Beitrage zur Kenntniss,' &c., 1844, s. 345.
+
+[884] 'Nouvelles Archives du Museum,' tom. i. p. 27.
+
+[885] As quoted by Sir J. Lubbock in 'Nat. Hist. Review,' 1862, p. 345.
+
+[886] 'Transact. Linn. Soc.,' vol. xxiv., 1863, p. 62.
+
+[887] 'Parthenogenesis,' 1849, pp. 25-26. Prof. Huxley has some excellent
+remarks ('Medical Times,' 1856, p. 637) on this subject, in reference to
+the development of star-fishes, and shows how curiously metamorphosis
+graduates into gemmation or zoid-formation, which is in fact the same as
+metagenesis.
+
+[888] Prof. J. Reay Greene, in Guenther's 'Record of Zoolog. Lit.,' 1865,
+p. 625.
+
+[889] Fritz Mueller's 'Fuer Darwin,' 1864, s. 65, 71. The highest authority
+on crustaceans, Prof. Milne Edwards, insists ('Annal. des Sci. Nat.,' 2nd
+series, Zoolog., tom. iii. p. 322) on their metamorphoses differing even in
+closely allied genera.
+
+[890] Prof. Allman, in 'Annals and Mag. of Nat. Hist.,' 3rd series, vol.
+xiii., 1864, p. 348; Dr. S. Wright, idem, vol. viii., 1861, p. 127. _See_
+also p. 358 for analogous statements by Sars.
+
+[891] 'Tissus Vivants,' 1866, p. 22.
+
+[892] 'Cellular Pathology,' translat. by Dr. Chance, 1860, pp. 14, 18, 83,
+460.
+
+[893] Paget, 'Surgical Pathology,' vol. i., 1853, pp. 12-14.
+
+[894] Idem, p. 19.
+
+[895] Mantegazza, quoted in 'Popular Science Review,' July 1865, p. 522.
+
+[896] 'De la Production Artificielle des Os,' p. 8.
+
+[897] Isidore Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. ii. pp.
+549, 560, 562; Virchow, idem, p. 484.
+
+[898] For the most recent classification of cells, _see_ Ernst Haeckel's
+'Generelle Morpholog.,' Band ii., 1866, s. 275.
+
+[899] 'The Structure and Growth of Tissues,' 1865, p. 21, &c.
+
+[900] Dr. W. Turner, 'The present Aspect of Cellular Pathology,' 'Edinburgh
+Medical Journal,' April, 1863.
+
+[901] This term is used by Dr. E. Montgomery ('On the Formation of
+so-called Cells in Animal Bodies,' 1867, p. 42), who denies that cells are
+derived from other cells by a process of growth, but believes that they
+originate through certain chemical changes.
+
+[902] Prof. Huxley has called my attention to the views of Buffon and
+Bonnet. The former ('Hist. Nat. Gen.,' edit. of 1749, tom. ii. pp. 54, 62,
+329, 333, 420, 425) supposes that organic molecules exist in the food
+consumed by every living creature; and that these molecules are analogous
+in nature with the various organs by which they are absorbed. When the
+organs thus become fully developed, the molecules being no longer required
+collect and form buds or the sexual elements. If Buffon had assumed that
+his organic molecules had been formed by each separate unit throughout the
+body, his view and mine would have been closely similar.
+
+Bonnet ('Oeuvres d'Hist. Nat.,' tom. v., part i., 1781, 4to edit., p. 334)
+speaks of the limbs having germs adapted for the reparation of all possible
+losses; but whether these germs are supposed to be the same with those
+within the buds and sexual organs is not clear. His famous but now exploded
+theory of _emboitement_ implies that perfect germs are included within
+germs in endless succession, pre-formed and ready for all succeeding
+generations. According to my view, the germs or gemmules of each separate
+part were not originally pre-formed, but are continually produced at all
+ages during each generation, with some handed down from preceding
+generations.
+
+Prof. Owen remarks ('Parthenogenesis,' 1849, pp. 5-8), "Not all the progeny
+of the primary impregnated germ-cell are required for the formation of the
+body in all animals: certain of the derivative germ-cells may remain
+unchanged and become included in that body which has been composed of their
+metamorphosed and diversely combined or confluent brethren: so included,
+any derivative germ-cell, or the nucleus of such, may commence and repeat
+the same processes of growth by imbibition, and of propagation by
+spontaneous fission, as those to which itself owed its origin;" &c. By the
+agency of these germ-cells Prof. Owen accounts for parthenogenesis, for
+propagation by self-division during successive generations, and for the
+repairs of injuries. His view agrees with mine in the assumed transmission
+and multiplication of his germ-cells, but differs fundamentally from mine
+in the belief that the primary germ-cell was formed within the ovarium of
+the female and was fertilised by the male. My gemmules are supposed to be
+formed, quite independently of sexual concourse, by each separate cell or
+unit throughout the body, and to be merely aggregated within the
+reproductive organs.
+
+Lastly, Mr. Herbert Spencer ('Principles of Biology,' vol. i., 1863-4,
+chaps. iv. and viii.) has discussed at considerable length what he
+designates as physiological units. These agree with my gemmules in being
+supposed to multiply and to be transmitted from parent to child; the sexual
+elements are supposed to serve merely as their vehicles; they are the
+efficient agents in all the forms of reproduction and in the repairs of
+injuries; they account for inheritance, but they are not brought to bear on
+reversion or atavism, and this is unintelligible to me; they are supposed
+to possess polarity, or, as I call it, affinity; and apparently they are
+believed to be derived from each separate part of the whole body. But
+gemmules differ from Mr. Spencer's physiological units, inasmuch as a
+certain number, or mass of them, are, as we shall see, requisite for the
+development of each cell or part. Nevertheless I should have concluded that
+Mr. Spencer's views were fundamentally the same with mine, had it not been
+for several passages which, as far as I understand them, indicate something
+quite different. I will quote some of these passages from pp. 254-256. "In
+the fertilised germ we have two groups of physiological units, slightly
+different in their structures."... "It is not obvious that change in the
+form of the part, caused by changed action, involves such change in the
+physiological units throughout the organism, that these, when groups of
+them are thrown off in the shape of reproductive centres, will unfold into
+organisms that have this part similarly changed in form. Indeed, when
+treating of Adaptation, we saw that an organ modified by increase or
+decrease of function can but slowly so react on the system at large as to
+bring about those correlative changes required to produce a new
+equilibrium; and yet only when such new equilibrium has been established,
+can we expect it to be _fully_ expressed in the modified physiological
+units of which the organism is built--only then can we count on a complete
+transfer of the modification to descendants."... "That the change in the
+offspring must, other things equal, be in the same direction as the change
+in the parent, we may dimly see is implied by the fact, that the change
+propagated throughout the parental system is a change towards a new state
+of equilibrium--a change tending to bring the actions of all organs,
+reproductive included, into harmony with these new actions."
+
+[903] M. Philipeaux ('Comptes Rendus,' Oct. 1, 1866, p. 576, and June,
+1867) has lately shown that when the entire fore-limb, including the
+scapula, is extirpated, the power of regrowth is lost. From this he
+concludes that it is necessary for regrowth that a small portion of the
+limb should be left. But as in the lower animals the whole body may be
+bisected and both halves be reproduced, this belief does not seem probable.
+May not the early closing of a deep wound, as in the case of the
+extirpation of the scapula, prevent the formation or protrusion of the
+nascent limb?
+
+[904] 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. xiv., 1850, p. 244.
+
+[905] _See_ some very interesting papers on this subject by Prof. Lionel
+Beale, in 'Medical Times and Gazette,' Sept. 9th, 1865, pp. 273, 330.
+
+[906] Third Report of the R. Comm. on the Cattle Plague, as quoted in
+'Gard. Chronicle,' 1866, p. 446.
+
+[907] In a cod-fish, weighing 20 lb., Mr. F. Buckland ('Land and Water,'
+1867, p. 57) calculated the above number of eggs. In another instance,
+Harmer ('Phil. Transact.,' 1767, p. 280) found 3,681,760 eggs. For the
+Ascaris, _see_ Carpenter's 'Comp. Phys.,' 1854, p. 590. Mr. J. Scott, of
+the Royal Botanic Garden of Edinburgh, calculated, in the same manner as I
+have done for some British orchids ('Fertilisation of Orchids,' p. 344),
+the number of seeds in a capsule of an Acropera, and found the number to be
+371,250. Now this plant produces several flowers on a raceme and many
+racemes during a season. In an allied genus, Gongora, Mr. Scott has seen
+twenty capsules produced on a single raceme: ten such racemes on the
+Acropera would yield above seventy-four millions of seed. I may add that
+Fritz Mueller informs me that he found in a capsule of a Maxillaria, in
+South Brazil, that the seed weighed 42-1/2 grains: he then arranged half a
+grain of seed in a narrow line, and by counting a measured length found the
+number in the half-grain to be 20,667, so that in the capsule there must
+have been 1,756,440 seeds! The same plant sometimes produces half-a-dozen
+capsules.
+
+[908] 'Annals and Mag. of Nat. Hist.,' 3rd series, vol. viii., 1861, p.
+490.
+
+[909] Paget, 'Lectures on Pathology,' p. 27; Virchow, 'Cellular Pathology,'
+translat. by Dr. Chance, pp. 123, 126, 294; Claude Bernard, 'Des Tissus
+Vivants,' pp. 177, 210, 337; Mueller's 'Physiology,' Eng. translat., p.
+290.
+
+[910] Virchow, 'Cellular Pathology,' trans. by Dr. Chance, 1860, pp. 60,
+162, 245, 441, 454.
+
+[911] Idem, pp. 412-426.
+
+[912] _See_ Rev. J. M. Berkeley, in 'Gard. Chron.,' April 28th, 1866, on a
+bud developed on the petal of the Clarkia. _See_ also H. Schacht, 'Lehrbuch
+der Anat.,' &c., 1859, Theile ii. s. 12, on adventitious buds.
+
+[913] Mr. Herbert Spencer ('Principles of Biology,' vol. ii. p. 430) has
+fully discussed the antagonism between growth and reproduction.
+
+[914] The male salmon is known to breed at a very early age. The Triton and
+Siredon, whilst retaining their larval branchiae, according to Filippi and
+Dumeril ('Annals and Mag. of Nat. Hist.,' 3rd series, 1866, p. 157), are
+capable of reproduction. Ernst Haeckel has recently ('Monatsbericht Akad.
+Wiss. Berlin,' Feb. 2nd, 1865) observed the surprising case of a medusa,
+with its reproductive organs active, which produces by budding a widely
+different form of medusa; and this latter also has the power of sexual
+reproduction. Krohn has shown ('Annals and Mag. of Nat. Hist.,' 3rd series,
+vol. xix., 1862, p. 6) that certain other medusae, whilst sexually mature,
+propagate by gemmae.
+
+[915] _See_ his excellent discussion on this subject in 'Nouvelles Archives
+du Museum,' tom. i. p. 151.
+
+[916] Various physiologists have insisted on this distinction between
+growth and development. Prof. Marshall ('Phil. Transact.,' 1864, p. 544)
+gives a good instance in microcephalous idiots, in which the brain
+continues to grow after having been arrested in its development.
+
+[917] 'Compte Rendu,' Nov. 14, 1864, p. 800.
+
+[918] As previously remarked by Quatrefages, in his 'Metamorphoses de
+l'Homme,' &c., 1862, p. 129.
+
+[919] Guenther's 'Zoological Record,' 1864, p. 279.
+
+[920] Sedgwick, in 'Medico-Chirurg. Review,' April 1863, p. 454.
+
+[921] Isid. Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. i., 1832, pp.
+435, 657; and tom. ii. p. 560.
+
+[922] Virchow, 'Cellular Pathology,' 1860, p. 66.
+
+[923] Moquin-Tandon, 'Teratologie Veg.,' 1841, pp. 218, 220, 353. For the
+case of the pea, _see_ 'Gardener's Chron.,' 1866, p. 897.
+
+[924] Mueller's 'Physiology,' Eng. translat., vol. i. p. 407.
+
+[925] _See_ some remarks to this effect by Sir H. Holland in his 'Medical
+Notes,' 1839, p. 32.
+
+[926] This is the view taken by Prof. Haeckel, in his 'Generelle
+Morphologie' (B. ii. s. 171), who says: "Lediglich die partielle Identitaet
+der specifischconstituirten Materie im elterlichen und im kindlichen
+Organismus, die Theilung dieser Materie bei der Fortpflanzung, ist die
+Ursache der Erblichkeit."
+
+[927] In these remarks I, in fact, follow Naudin, who speaks of the
+elements or essences of the two species which are crossed. See his
+excellent memoir in the 'Nouvelles Archives du Museum,' tom. i. p. 151.
+
+[928] Godron, 'De l'Espece,' 1859, tom. ii. p. 44, &c.
+
+[929] Journal Proc. Linn. Soc., 1858, vol. iii. p. 60.
+
+[930] 'The Quarterly Journal of Science,' Oct. 1867, p. 486.
+
+[931] M. Rufz de Lavison, in 'Bull. Soc. Imp. d'Acclimat.,' Dec. 1862, p.
+1009.
+
+[932] 'Races of Man,' 1850, p. 315.
+
+[933] 'Travels in Peru,' Eng. translat., p. 177.
+
+[934] Youatt on Cattle, 1834, p 200: on Pigs; _see_ 'Gard. Chronicle,'
+1854, p. 410.
+
+[935] 'Die Pflanzen der Pfahlbauten,' 1865.
+
+[936] Morlot, 'Soc. Vaud. des Scien. Nat,' Mars 1860, p. 298.
+
+[937] Ruetimeyer, 'Die Fauna der Pfahlbauten,' 1861, s. 30.
+
+[938] Godron, 'De l'Espece,' tom. i., 1859, p. 368.
+
+[939] 'Geographie Botan.,' 1855, p. 989.
+
+[940] Pickering, 'Races of Man,' 1850, p. 318.
+
+[941] 'Journal of a Horticultural Tour,' by a Deputation of the Caledonian
+Hist. Soc., 1823, p. 293.
+
+
+
+
+
+       *       *       *       *       *
+
+
+
+
+
+Corrections made to printed original.
+
+p. iii. "APPEARANCE WITH ADVANCING AGE": 'ARPEARANCE' in original.
+
+p. vi. "SLIGHT CHANGES SUFFICIENT": 'SUFFICENT' in original.
+
+p. 61. "bearing in mind what has been said": 'bearnig' in original.
+
+p. 78. "not attached to any particular period": 'particuliar' in original.
+
+p. 243. "it permits innumerable individuals to be born": 'permitts' in
+original.
+
+p. 294. "liable to complete absorption": 'absortion' in original.
+
+p. 297. "found that when the animal was compelled ...": 'found than ...' in
+original.
+
+p. 318. "branches in a rudimentary condition": 'rudimentry' in original.
+
+p. 384. "force themselves into a minute orifice": 'into' was printed on
+next line in original, after 'must'.
+
+
+
+***END OF THE PROJECT GUTENBERG EBOOK THE VARIATION OF ANIMALS AND PLANTS
+UNDER DOMESTICATION, VOLUME II (OF 2)***
+
+
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