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diff --git a/44849-8.txt b/44849-8.txt deleted file mode 100644 index 7ba1c05..0000000 --- a/44849-8.txt +++ /dev/null @@ -1,5719 +0,0 @@ -Project Gutenberg's Colouration in Animals and Plants, by Alfred Tylor - -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: Colouration in Animals and Plants - -Author: Alfred Tylor - -Editor: Sydney B. J. Skertchly - -Release Date: February 9, 2014 [EBook #44849] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK COLOURATION IN ANIMALS AND PLANTS *** - - - - -Produced by Chris Curnow, Nicole Henn-Kneif, Tom Cosmas -and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - -Transcriber's Note - - Italic text has been formatted as _text_ and superscript text as ^{text}. - - - - - COLOURATION - IN - ANIMALS AND PLANTS. - - BY THE LATE - ALFRED TYLOR, F.G.S. - - _Edited by_ - SYDNEY B. J. SKERTCHLY, F.G.S., - LATE OF H.M. GEOLOGICAL SURVEY. - - LONDON: - PRINTED BY ALABASTER, PASSMORE, AND SONS, - FANN STREET, ALDERSGATE STREET, E.C. - - 1886. - - - - - IN MEMORY - OF A FRIENDSHIP OF MANY YEARS, - THIS BOOK - IS - Affectionately Inscribed - TO - THE RIGHT HON. GEORGE YOUNG, P.C. - 1885. - - - - - PREFACE. - - -This little book is only a sketch of what its Author desired it to be, -and he never saw the completed manuscript. Beginning with the -fundamental idea that decoration is based upon structure, he saw that -this was due to the fact that in the lower, transparent, animals, colour -is applied directly to the organs, and that the decoration of opaque -animals is carried out on the same principle--the primitive idea being -maintained. Where function changes the pattern alters, where function is -localized colour is concentrated: and thus the law of emphasis was -evolved. Symmetry was a necessary consequence, for like parts were -decorated alike, and this symmetry was carried out in detail apparently -for the sake of beauty, as in the spiracular markings of many larvæ. -Hence the reason for recognizing the law of repetition. - -With the developing of these ideas the necessity for recognizing some -sort of consciousness even in the lowest forms of life was forced upon -the Author, until inherited memory formed part of his scientific faith. -This he saw dimly years ago, but only clearly when Mr. S. Butler's -remarkable "Life and Habit" appeared, and he was gratified and -strengthened when he found Mr. Romanes adopting that theory in his -"Mental Evolution." - -The opening chapters are designedly elementary; for the Author had a -wise dread of locking intellectual treasures in those unpickable -scientific safes of which "the learned" alone hold keys. - -Only a very small portion of the vast array of facts accumulated has -been made use of, and the Author was steadily working through the -animal kingdom, seeking exceptions to his laws, but finding none, when -death closed his patient and far-seeing eyes. A few days before the end -he begged me to finish this abstract, for I had been at his side through -all his labours. - -The work contains his views as clearly as I could express them, though -on every page I feel they suffer from want of amplification. But I -feared the work might become the expression of my own thoughts, though -want of leisure would probably have prevented that unhappy result. Now -it is finished, I would fain write it all over again, for methinks -between the lines can be seen gleams of brighter light. - - SYDNEY B. J. SKERTCHLY. - - CARSHALTON, - _July 17th, 1886_. - - - The coloured illustrations were drawn by Mrs. Skertchly chiefly from - nature, and very carefully printed by Messrs. Alabaster, Passmore, and - Sons. - - - [Illustration] - - - - - CONTENTS. - - - CHAPTER PAGE - - I. INTRODUCTORY 1 - - II. INHERITED MEMORY 8 - - III. INTRODUCTORY SKETCH 16 - - IV. COLOUR, ITS NATURE AND RECOGNITION 25 - - V. THE COLOUR SENSE 32 - - VI. SPOTS AND STRIPES 39 - - VII. COLOURATION IN THE INVERTEBRATA 49 - - VIII. DETAILS OF PROTOZOA 56 - - IX. DETAILS OF COELENTERATA 59 - - X. THE COLOURATION OF INSECTS 68 - - XI. THE COLOURATION OF INSECTS 75 - - XII. ARACHNIDA 82 - - XIII. COLOURATION OF INVERTEBRATA 85 - - XIV. COLOURATION OF VERTEBRATA 88 - - XV. THE COLOURATION OF PLANTS 95 - - XVI. CONCLUSIONS 97 - - - - - LIST OF WOODCUTS. - - - Fig. 1. Part of Secondary Feather of Argus Pheasant. - - Fig. 2. Ditto Wing-feather of ditto. - - Fig. 3. Diagram of Butterfly's Wing. - - Fig. 4. Python. - - Fig. 5. Tiger's Skin. - - Fig. 6. Ditto. - - Fig. 7. Tiger's Head, side view. - - Fig. 8. Ditto, crown. - - Fig. 9. Leopard's Skin. - - Fig. 10. Ditto. - - Fig. 11. Leopard's Head, side view. - - Fig. 12. Ditto, crown. - - Fig. 13. Lynx' Skin. - - Fig. 14. Ditto. - - Fig. 15. Ocelot. - - Fig. 16. Badger. - - Fig. 17. Begonia Leaf. - - - - - DESCRIPTION OF PLATES. - - - PLATE I. _Kallima Inachus_, the Indian Leaf Butterfly. - _p._ 28. Fig. 1. With wings expanded. - Fig. 2. Two Butterflies at rest, showing their exact - resemblance to dead leaves. - This insect affords one of the best examples of - protective resemblance. - - - PLATE II. Illustration of mimicry in butterflies. - _p._ 30. Fig. 1. Male of _Papilio merope_. - Fig. 2. Female of ditto mimicking Fig. 3. - Fig. 3. _Danais niavius._ - On the African continent both species occur, but in - Madagascar _D. niavius_ is wanting, and the female - _P. merope_ is coloured like the male. - - - PLATE III. Fig. 1. _Gonepteryx Cleopatra._ - _p._ 40. Fig. 2. _Gonepteryx rhamni_, male. - _Note._--The orange spot in Fig. 2 has - spread over the wing in Fig. 1. - Fig. 3. _Vanessa Antiopa._ - Fig. 4. _Panopoea hirta._ - Fig. 5. _Acrea gea._ - These two last belong to widely different genera, but - are admirable examples of mimicry. - - - PLATE IV. Fig. 1. _Leucophasia Sinapis._ - _p._ 42. Fig. 2. Ditto, var. _diniensis_. - Fig. 3. _Anthocaris cardamines_, male. - Fig. 4. Ditto, female. - Fig. 5. _Anthocaris belemia._ - Fig. 6. _Anthocaris belia._ - Fig. 7. Ditto, var. _simplonia_. - Fig. 8. _Anthocaris eupheno_, female. - Fig. 9. Ditto, male. - Fig. 10. _Anthocaris euphemoides._ - Fig. 11. _Papilio machaon._ - Fig. 12. _Papilio podalirius._ - Fig. 13. _Pieris napi_, summer form. - Fig. 14. Ditto, winter form. - Fig. 15. Ditto, var. _bryoniæ_ (alpine form). - Fig. 16. Ditto, summer form, underside. - Fig. 17. Ditto, winter form, underside. - Fig. 18. Ditto, var. _bryoniæ_, underside. - - Figs. 13-18 illustrate admirably the variations of the - yellow and black in the same species. - - - PLATE V. Fig. 1. _Araschnia prorsa_, male. - _p._ 44. Fig. 2. Ditto, female. - Fig. 3. _Araschnia levana_, female. - Fig. 4. Ditto, male. - Fig. 5. _Paragra ægeria._ - Fig. 6. _Araschnia porima._ - Fig. 7. Ditto, var. _meione_. - Fig. 8. _Grapta interrogationis._ - Fig. 9. Ditto. - Fig. 10. Ditto. - Fig. 11. _Papilio Ajax_, var. _Walshii_. - Fig. 12. Ditto, var. _telamonides_. - Fig. 13. Ditto, var. _Marcellus_. - - Figs. 1-5 are all one species; _levana_ being the winter form, - _prorsa_ the summer form, and _porima_ intermediate. Similarly - 6-7 are the same species, _meione_ being the southern form. So - with 8-9 and 11-13, which are only seasonal varieties. Here we - can actually trace the way in which varieties are formed. - _See_ Weismann's work, cited in the text. - - - PLATE VI. _Syncoryne pulchella_, magnified. After Professor Allman. - _p._ 62. Gymnoblastic or Tubularian Hydroids. Ray Soc., 1871, - pl. vi., figs. 1 and 3. - - Fig. 1. A planoblast as seen passively floating in the water - after liberation. - Fig. 2. The entire hydrosoma of syncoryne. - _a._ The spadix. - _b._ The medusæ or planoblasts in various stages of - development. - - - PLATE VII. - _p._ 80. Fig. 1. _Deilephila galii_, immature. - Fig. 2. Ditto brown variety, adult. - Fig. 3. _Deilephila euphorbiæ._ - Fig. 4. _Sphinx ligustri._ - Fig. 5. _Deilephila euphorbiæ_, dorsal view. - Fig. 6. _Orgyia antiqua._ - Fig. 7. _Abraxas grossulariata._ - Fig. 8. _Bombyx neustria._ - Fig. 9. _Callimorpha dominula._ - Fig. 10. _Euchelia jacobæa._ - Fig. 11. _Papilio machaon._ - - - SPIDERS. - - PLATE VIII. Fig. 1. _Segestria senoculata_, female. - _p._ 84. Fig. 2. _Sparassus smaragdulus_, male. - Fig. 3. _Lycosa piscatoria_, female. - Fig. 4. ---- _andrenivora_, male. - Fig. 5. ---- ---- female. - Fig. 6. ---- _allodroma_, male. - Fig. 7. ---- _agretyca_, male. - Fig. 8. ---- _allodroma_, female. - Fig. 9. Diagram of _Lycosa_, showing form and position of - vessels. After Gegenbaur. - Fig. 10. _Lycosa campestris_, female. - Fig. 11. _Thomisus luctuosus_, male. - Fig. 12. _Salticus scenicus_, female. - Fig. 13. _Lycosa rapax_, female. - Fig. 14. ---- _latitans_, female. - Fig. 15. _Theridion pictum_, female. - Fig. 16. _Lycosa picta_, female. - Fig. 17. ---- ---- male. - All the above are British species, and copied from Blackwell's - "Spiders of Great Britain and Ireland." Ray Soc., 1862. - - - FISHES. - - PLATE IX. Fig. 1. Windermere Char. _Salmo Willughbii._ A species - _p._ 88. peculiar to our North of England lakes. - Fig. 2. Perch, _Perca fluviatilis_, showing the modified - rib-like markings. - - - SUNBIRDS. - - PLATE X. Fig. 1. _Nectarinea chloropygia._ - _p._ 90. Fig. 2. _Nectarinea christinæ._ - These birds illustrate regional colouration well. - - - LEAVES. - - PLATE XI. Fig. 1. Horse Chestnut, _Æschulus hippocastanum_, decaying. - _p._ 95. Fig. 2. _Coleus._ - Fig. 3. _Begonia rex._ - Fig. 4. _Begonia_. - Fig. 5. _Caladium bicolor._ - Fig. 6. _Anoechtochilus xanthophyllus._ - - - FLOWERS. - - PLATE XII. Fig. 1. _Gloxinia_, with 5 petals, showing uneven - _p._ 96. colouring. - Fig. 2. _Gloxinia_, with 6 petals, showing regular - colouring. - Figs. 3 and 4. Pelargoniums, showing the variation of the - dark markings with the different sized petals. - - - [Illustration] - - - - - COLOURATION IN ANIMALS AND PLANTS. - - - - - CHAPTER I. - - INTRODUCTION. - - -Before Darwin published his remarkable and memorable work on the Origin -of Species, the decoration of animals and plants was a mystery as much -hidden to the majority as the beauty of the rainbow ere Newton analysed -the light. That the world teemed with beauty in form and colour was all -we knew; and the only guess that could be made as to its uses was the -vague and unsatisfactory suggestion that it was appointed for the -delight of man. - -Why, if such was the case, so many flowers were "born to blush unseen," -so many insects hidden in untrodden forests, so many bright-robed -creatures buried in the depths of the sea, no man could tell. It seemed -but a poor display of creative intelligence to lavish for thousands of -years upon heedless savage eyes such glories as are displayed by the -forests of Brazil; and the mind recoiled from the suggestion that such -could ever have been the prime intention. - -But with the dawn of the new scientific faith, light began to shine upon -these and kindred questions; nature ceased to appear a mass of useless, -unconnected facts, and ornamentation appeared in its true guise as of -extreme importance to the beings possessing it. It was the theory of -descent with modification that threw this light upon nature. - -This theory, reduced to its simplest terms, is that species, past and -present, have arisen from the accumulation by inheritance of minute -differences of form, structure, colour, or habit, giving to the -individual a better chance, in the struggle for existence, of obtaining -food or avoiding danger. It is based on a few well-known and universally -admitted facts or laws of nature: namely, the law of multiplication in -geometrical progression causing the birth of many more individuals than -can survive, leading necessarily to the struggle for existence; the law -of heredity, in virtue of which the offspring resembles its parents; the -law of variation, in virtue of which the offspring has an individual -character slightly differing from its parents. - -To illustrate these laws roughly we will take the case of a bird, say, -the thrush. The female lays on the average five eggs, and if all these -are hatched, and the young survive, thrushes would be as seven to two -times as numerous in the next year. Let two of these be females, and -bring up each five young; in the second year we shall have seventeen -thrushes, in the third thirty-seven, in the fourth seventy-seven, and so -on. Now common experience tells us not merely that such a vast increase -of individuals does not take place, but can never do so, as in a very -few years the numbers would be so enormously increased that food would -be exhausted. - -On the other hand, we know that the numbers of individuals remain -practically the same. It follows, then, that of every five eggs four -fail to arrive at maturity; and this rigorous destruction of individuals -is what is known as the struggle for existence. If, instead of a bird, -we took an insect, laying hundreds of eggs, a fish, laying thousands, or -a plant, producing still greater quantities of seed, we should find the -extermination just as rigorous, and the numbers of individuals destroyed -incomparably greater. Darwin has calculated that from a single pair of -elephants nearly nineteen millions would be alive in 750 years if each -elephant born arrived at maturity, lived a hundred years, and produced -six young--and the elephant is the slowest breeder of all animals. - -The struggle for existence, then, is a real and potent fact, and it -follows that if, from any cause whatever, a being possesses any power or -peculiarity that will give it a better chance of survival over its -fellows--be that power ever so slight--it will have a very decided -advantage. - -Now it can be shown that no two individuals are exactly alike, in other -words, that variation is constantly taking place, and that no animal or -plant preserves its characters unmodified. This we might have expected -if we attentively consider how impossible it is for any two individuals -to be subjected to exactly the same conditions of life and habit. But -for the proofs of variability we have not to rely upon theoretical -reasoning. No one can study, even superficially, any class or species -without daily experiencing the conviction that no two individuals are -alike, and that variation takes place in almost every conceivable -direction. - -Granted then the existence of the struggle for existence and the -variability of individuals, and granting also that if any variation -gives its possessor a firmer hold upon life, it follows as a necessity -that the most favoured individuals will have the best chance of -surviving and leaving descendants, and by the law of heredity, we know -these offspring will tend to inherit the characters of their parents. -This action is often spoken of as the preservation of favoured races, -and as the survival of the fittest. - -The gradual accumulation of beneficial characters will give rise in time -to new varieties and species; and in this way primarily has arisen the -wonderful diversity of life that now exists. Such, in barest outline, is -the theory of descent with modification. - -Let us now see in what way this theory has been applied to colouration. -The colours, or, more strictly, the arrangement of colours, in patterns -is of several kinds, viz.:-- - -1. _General Colouration_, or such as appears to have no very special -function _as_ colour. We find this most frequently in the vegetable -kingdom, as, for instance, the green hue of leaves, which, though it has -a most valuable function chemically has no particular use as colour, so -far as we can see. - -2. _Distinctive Colouration_, or the arrangement of colours in different -patterns or tints corresponding to each species. This is the most usual -style of colouring, and the three following kinds are modifications of -it. It is this which gives each species its own design, whether in -animals or plants. - -3. _Protective Resemblance_, or the system of colouring which conceals -the animal from its prey, or hides the prey from its foe. Of this class -are the green hues of many caterpillars, the brown tints of desert -birds, and the more remarkable resemblances of insects to sticks and -leaves. - -4. _Mimetic Colouration_, or the resemblance of one animal to another. -It is always the resemblance of a rare species, which is the favourite -food of some creature, to a common species nauseous to the mimicker's -foe. Of this character are many butterflies. - -5. _Warning Colours_, or distinctive markings and tints rendering an -animal conspicuous, and, as it were, proclaiming _noli me tangere_ to -its would-be attackers. - -6. _Sexual Colours_, or particular modifications of colour in the two -sexes, generally taking the form of brilliancy in the male, as in the -peacock and birds of paradise. - -Under one or other of these headings most schemes of colouration will be -found to arrange themselves. - -At the outset, and confining ourselves to the animal kingdom for the -present, bearing in mind the fierce intensity of the struggle for life, -it would seem that any scheme of colour that would enable its possessor -to elude its foes or conceal itself from its prey, would be of vital -importance. Hence we might infer that protective colouring would be a -very usual phenomenon; and such we find to be the case. In the sea we -have innumerable instances of protective colouring. Fishes that lie upon -the sandy bottom are sand-coloured, like soles and plaice, in other -orders we find the same hues in shrimps and crabs, and a common species -on our shores (_Carcinus mænas_) has, just behind the eyes, a little -light irregular patch, so like the shell fragments around that when it -hides in the sand, with eyes and light spot alone showing, it is -impossible to distinguish it. - -The land teems with protective colours. The sombre tints of so many -insects, birds and animals are cases in point, as are the golden coat of -the spider that lurks in the buttercup, and the green mottlings of the -underwings of the orange-tip butterfly. Where absolute hiding is -impossible, as on the African desert, we find every bird and insect, -without exception, assimilating the colour of the sand. - -But if protective colour is thus abundant, it is no less true that -colour of the most vivid description has arisen for the sole purpose of -attracting notice. We observe this in the hues of many butterflies, in -the gem-like humming birds, in sun-birds, birds of paradise, peacocks -and pheasants. To see the shining metallic blue of a Brazilian Morpho -flashing in the sun, as it lazily floats along the forest glades, is to -be sure that in such cases the object of the insect is to attract -notice. - -These brilliant hues, when studied, appear to fall into two classes, -having very diverse functions, namely Sexual and Warning Colours. - -Protection is ensured in many ways, and among insects one of the -commonest has been the acquisition of a nauseous flavour. This is often -apparent even to our grosser senses; and the young naturalist who -captures his first crimson-and-green Burnet Moth or Scarlet Tiger, -becomes at once aware of the existence of a fetid greasy secretion. This -the insectivorous birds know so well that not one will ever eat such -insects. But unless there were some outward and visible sign of this -inward and sickening taste, it would little avail the insect to be first -killed and then rejected. Hence these warning colours--they as -effectively signal danger as the red and green lamps on our railways. - -It may here be remarked that wherever mimickry occurs in insects, the -species mimicked is always an uneatable one, and the mimicker a -palatable morsel. It is nature's way of writing "poison" on her -jam-pots. - -The other class of prominent colours--the Sexual--have given rise to two -important theories, the one by Darwin, the counter-theory by Wallace. - -Darwin's theory of Sexual Selection is briefly this:--He points out in -much detail how the male is generally the most powerful, the most -aggressive, the most ardent, and therefore the wooer, while the female -is, as a rule, gentler, smaller, and is wooed or courted. He brings -forward an enormous mass of well-weighed facts to show, for example, how -often the males display their plumes and beauties before their loves in -the pairing season, and his work is a long exposition of the truth that -Tennyson proclaimed when he wrote:-- - - "In the spring a fuller crimson comes upon the robin's breast, - In the spring the wanton lapwing gets himself another crest, - In the spring a livelier iris changes on the burnished dove, - In the spring the young man's fancy lightly turns to thoughts of love." - -That birds are eminently capable of appreciating beauty is certain, and -numerous illustrations are familiar to everyone. Suffice it here to -notice the pretty Bower Birds of Australia, that adorn their love -arbours with bright shells and flowers, and show as unmistakable a -delight in them as the connoisseur among his art treasures. - -From these and kindred facts Darwin draws the conclusion that the -females are most charmed with, and select the most brilliant males, and -that by continued selection of this character, the sexual hues have been -gradually evolved. - -To this theory Wallace takes exception. Admitting, as all must, the fact -of sexually distinct ornamentation, he demurs to the conclusion that -they have been produced by sexual selection. - -In the first place, he insists upon the absence of all proof that the -least attractive males fail to obtain partners, without which the theory -must fail. Next he tells us that it was the case of the Argus pheasant, -so admirably worked out by Darwin, that first shook his faith in sexual -selection. Is it possible, he asks, that those exquisite eye-spots, -shaded "like balls lying loose within sockets" (objects of which the -birds could have had no possible experience) should have been produced -... "through thousands and tens of thousands of female birds, all -preferring those males whose markings varied slightly in this one -direction, this uniformity of choice continuing through thousands and -tens of thousands of generations"?[1] - -As an alternative explanation, he would advance no new theory, but -simply apply the known laws of evolution. He points out, and dwells -upon, the high importance of protection to the female while sitting on -the nest. In this way he accounts for the more sombre hues of the -female; and finds strong support in the fact that in those birds in -which the male undertakes the household duties, he is of a domestic dun -colour, and his gad-about-spouse is bedizened like a country-girl at -fair time. - -With regard to the brilliant hues themselves, he draws attention to the -fact that depth and intensity of colour are a sign of vigour and -health--that the pairing time is one of intense excitement, and that we -should naturally expect to find the brightest hues then displayed. -Moreover, he shows--and this is most important to us--that "the most -highly-coloured and most richly varied markings occur on those parts -which have undergone the greatest modification, or have acquired the -most abnormal development."[2] - -It is not our object to discuss these rival views; but they are here -laid down in skeleton, that the nature of the problem of the principles -of colouration may be easily understood. - -Seeing, then, how infinitely varied is colouration, and how potently -selection has modified it, the question may be asked, "Is it possible -to find any general system or law which has determined the main plan of -decoration, any system which underlies natural selection, and through -which it works"? We venture to think there is; and the object of this -work is to develop the laws we have arrived at after several years of -study. - - - [Illustration] - - - [1] Wallace, Tropical Nature, p. 206. - [2] _Op. cit._, p. 206. - - - - - CHAPTER II. - - INHERITED MEMORY. - - -Many of our observations seemed to suggest a quasi-intelligent action on -the part of the beings under examination; and we were led, early in the -course of our studies, to adopt provisionally the hypothesis that memory -was inherited--that the whole was consequently wiser than its parts, the -species wiser than the individual, the genus wiser than the species. - -One illustration will suffice to show the possibility of memory being -inherited. Chickens, as a rule, are hatched with a full knowledge of how -to pick up a living, only a few stupid ones having to be taught by the -mother the process of pecking. When eggs are hatched artificially, -ignorant as well as learned chicks are produced, and the less -intelligent, having no hen instructor, would infallibly die in the midst -of plenty. But if a tapping noise, like pecking, be made near them, they -hesitate awhile, and then take to their food with avidity. Here the -tapping noise seems certainly to have awakened the ancestral memory -which lay dormant. - -It may be said all this is habit. But what is habit? Is it any -explanation to say a creature performs a given action by habit? or is it -not rather playing with a word which expresses a phenomenon without -explaining it? Directly we bring memory into the field we get a real -explanation. A habit is acquired by repetition, and could not arise if -the preceding experience were forgotten. Life is largely made up of -repetition, which involves the formation of habits; and, indeed, -everyone's experience (habit again) shows that life only runs smoothly -when certain necessary habits have been acquired so perfectly as to be -performed without effort. A being at maturity is a great storehouse of -acquired habits; and of these many are so perfectly acquired, _i.e._, -have been performed so frequently, that the possessor is quite -unconscious of possessing them. - -Habit tends to become automatic; indeed, a habit can hardly be said to -be formed until it is automatic. But habits are the result of experience -and repetition, that is, have arisen in the first instance by some -reasoning process; and reasoning implies consciousness. Nevertheless, -the action once thought out, or reasoned upon, requires less conscious -effort on a second occasion, and still less on a third, and so on, until -the mere occurrence of given conditions is sufficient to ensure -immediate response without conscious effort, and the action is performed -mechanically or automatically: it is now a true habit. Habit, then, -commences in consciousness and ends in unconsciousness. To say, -therefore, when we see an action performed without conscious thought, -that consciousness has never had part in its production, is as illogical -as to say that because we read automatically we can never have learned -to read. - -The thorough appreciation of this principle is absolutely essential to -the argument of this work; for to inherited memory we attribute not only -the formation of habits and instincts, but also the modification of -organs, which leads to the formation of new species. In a word, it is to -memory we attribute the possibility of evolution, and by it the struggle -for existence is enabled to re-act upon the forms of life, and produce -the harmony we see in the organic world. - -Our own investigations had led us very far in this direction; but we -failed to grasp the entire truth until Mr. S. Butler's remarkable work, -"Life and Habit," came to our notice. This valuable contribution to -evolution smoothed away the whole of the difficulties we had -experienced, and enabled us to propound the views here set forth with -greater clearness than had been anticipated. - -The great difficulty in Mr. Darwin's works is the fact that he starts -with variations ready made, without trying, as a rule, to account for -them, and then shows that if these varieties are beneficial the -possessor has a better chance in the great struggle for existence, and -the accumulation of such variations will give rise to new species. This -is what he means by the title of his work, "The Origin of Species by -means of Natural Selection or the Preservation of Favoured Races in the -Struggle for Life." But this tells us nothing whatever about the origin -of species. As Butler puts it, "Suppose that it is an advantage to a -horse to have an especially broad and hard hoof: then a horse born with -such a hoof will, indeed, probably survive in the struggle for -existence; but he was not born with the larger and harder hoof _because -of his subsequently surviving_. He survived because he was born fit--not -he was born fit because he survived. The variation must arise first and -be preserved afterwards."[3] - -Mr. Butler works out with admirable force the arguments, first, that -habitual action begets unconsciousness; second, that there is a unity of -personality between parent and offspring; third, that there is a memory -of the oft-repeated acts of past existences, and, lastly, that there is -a latency of that memory until it is re-kindled by the presence of -associated ideas. - -As to the first point, we need say no more, for daily experience -confirms it; but the other points must be dealt with more fully. - -Mr. Butler argues for the absolute identity of the parent and offspring; -and, indeed, this is a necessity. Personal identity is a phrase, very -convenient, it is true, but still only a provisional mode of naming -something we cannot define. In our own bodies we say that our identity -remains the same from birth to death, though we know that our bodily -particles are ever changing, that our habits, thoughts, aspirations, -even our features, change--that we are no more really the same person -than the ripple over a pebble in a brook is the same from moment to -moment, though its form remains. If our personal identity thus elude our -search in active life, it certainly becomes no more tangible if we trace -existence back into pre-natal states. We _are_, in one sense, the same -individual; but, what is equally important, we _were_ part of our -mother, as absolutely as her limbs are part of her. There is no break of -continuity between offspring and parent--the river of life is a -continuous stream. We judge of our own identity by the continuity which -we see and appreciate; but that greater continuity reaching backwards -beyond the womb to the origin of life itself is no less a fact which -should be constantly kept in view. The individual, in reality, never -dies; for the lamp of life never goes out. - -For a full exposition of this problem, Mr. Butler's "Life and Habit" -must be consulted, where the reader will find it treated in a masterly -way. - -This point was very early appreciated in our work; and in a -paper read before the Anthropological Institute[4] in the year 1879, -but not published, this continuity was insisted upon by means of -diagrams, both of animal and plant life, and its connection with heredity -was clearly shown, though its relation to memory was only dimly -seen. From this paper the following passage may be quoted: "If, as -I believe, the origin of form and decoration is due to a process similar -to the visualising of object-thoughts in the human mind, the power -of this visualising must commence with the life of the being. It -would seem that this power may be best understood by a correct -insight into biological development. It has always excited wonder -that a child, a separate individual, should inherit and reproduce the -characters of its parents, and, indeed, of its ancestors; and the -tendency of modern scientific writing is often to make this obscure -subject still darker. But if we remember that the great law of all -living matter is, that the child is _not_ a separate individual, but a -part of the living body of the parent, up to a certain date, when it -assumes a separate existence, then we can comprehend how living -beings inherit ancestral characters, for they are parts of one continuous -series in which not a single break has existed or can ever -take place. Just as the wave-form over a pebble in a stream -remains constant, though the particles of water which compose it -are ever changing, so the wave-form of life, which is heredity, -remains constant, though the bodies which exhibit it are continually -changing. The retrospection of heredity and memory, and the -prospection of thought, are well shown in Mrs. Meritt's beautiful -diagram." - -This passage illustrates how parallel our thoughts were to Mr. Butler's, -whose work we did not then know. What we did not see at the time was, -that the power of thinking or memory might antedate birth. It is quite -impossible adequately to express our sense of admiration of Mr. Butler's -work. - -Granting then the physical identity of offspring and parent, the -doctrine of heredity becomes plain. The child becomes like the parent, -because it is placed in almost identical circumstances to those of its -parent, and is indeed part of that parent. If memory be possessed by all -living matter, and this is what we now believe, we can clearly see how -heredity acts. The embryo develops into a man like its parent, because -human embryos have gone through this process many times--till they are -unconscious of the action, they know how to proceed so thoroughly. - -Darwin, after deeply pondering over the phenomena of growth, repair of -waste and injury, heredity and kindred matters, advanced what he wisely -called a provisional hypothesis--pangenesis. - -"I have been led," he remarks, "or, rather, forced, to form a view which -to a certain extent, connects these facts by a tangible method. Everyone -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 ovules, but occasionally on the mother form; -how a hybrid can be produced by the union of the cellular tissue of two -plants independently of the organs of generation; how a limb can be -reproduced on the exact line of amputation, with neither too much nor -too little added; how the same organism may be produced by such widely -different processes as budding and true seminal generation; and, lastly, -how of two allied forms, one passes in the course of its development -through the most complex metamorphoses, and the other does not do so, -though when mature both are alike in every detail of structure. I am -aware that my view is merely a provisional hypothesis or speculation; -but until a better one be advanced, it will serve to bring together a -multitude of facts which are at present left disconnected by any -efficient cause."[5] - -After showing in detail that the body is made up of an infinite number -of units, each of which is a centre of more or less independent action, -he proceeds as follows:-- - -"It is universally admitted that the cells or units of the body increase -by self-division or proliferation, retaining the same nature, and that -they ultimately become converted into the various tissues of the -substances of the body. But besides this means of increase I assume that -the units throw off minute granules, which are dispersed throughout the -whole system; that these, when supplied with proper nutriment, multiply -by self-division, and are ultimately developed into units like those -from which they were originally derived. These granules may be called -gemmules. They are collected from all parts of the system to constitute -the sexual elements, and their development in the next generations forms -a new being; but they are likewise capable of transmission in a dormant -state to future generations, and may then be developed. Their -development depends on their union with other partially developed or -nascent cells, which precede them in the regular course of growth.... -Gemmules are supposed to be thrown off by every unit; not only during -the adult state, but during each stage of development of every organ; -but not necessarily during the continued existence of the same unit. -Lastly, I assume that the gemmules in their dormant state have a mutual -affinity for each other, leading to their aggregation into buds, or into -the sexual elements. Hence, it is not the reproductive organs or buds -which generate new organisms, but the units of which each individual is -composed."[6] - -Now, suppose that instead of these hypothetic gemmules we endow the -units with memory in ever so slight a degree, how simple the explanation -of all these facts becomes! What an unit has learned to do under given -conditions it can do again under like circumstances. Memory _does_ pass -from one unit to another, or we could not remember anything as men that -happened in childhood, for we are not physically composed of the same -materials. It is not at all necessary that an unit should remember it -remembers any more than we in reading are conscious of the efforts we -underwent in learning our letters. Few of us can remember learning to -walk, and none of us recollect learning to talk. Yet surely the fact -that we do read, and walk, and talk, proves that we have not forgotten -how. - -Bearing in mind, then, the fundamental laws that the offspring is one in -continuity with its parents, and that memory arises chiefly from -repetition in a definite order (for we cannot readily reverse the -process--we cannot sing the National Anthem backwards), it is easy to -see how the oft-performed actions of an individual become its -unconscious habits, and these by inheritance become the instincts and -unconscious actions of the species. Experience and memory are thus the -key-note to the origin of species. - -Granting that all living matter possesses memory, we must admit that all -actions are at first conscious in a certain degree, and in the "sense of -need" we have the great stimulation to action. - -In Natural Selection, as expounded by Mr. Darwin, there is no principle -by which small variations can be accumulated. Take any form, and let it -vary in all directions. We may represent the original form by a spot, -and the variations by a ring of dots. Each one of these dots may vary in -all directions, and so other rings of dots must be made, and so on, the -result not being development along a certain line, but an infinity of -interlacing curves. The tree of life is not like this. It branches ever -outwards and onwards. The eyes of the Argus pheasant and peacock have -been formed by the accumulation, through long generations, of more and -more perfect forms; the mechanism of the eye and hand has arisen by the -gradual accumulation of more and more perfect forms, and these processes -have been continued along definite lines. - -If we grant memory we eliminate this hap-hazard natural selection. We -see how a being that has once begun to perform a certain action will -soon perform it automatically, and when its habits are confirmed its -descendants will more readily work in this direction than any other, and -so specialisation may arise. - -To take the cases of protective resemblance and mimicry. Darwin and -Wallace have to start with a form something like the body mimicked, -without giving any idea as to how that resemblance could arise. But with -this key of memory we can open nature's treasure house much more fully. -Look, for instance, at nocturnal insects; and one need not go further -than the beetles (_Blatta_) in the kitchen, to see that they have a -sense of need, and use it. Suddenly turn up the gas, and see the hurried -scamper of the alarmed crowd. They are perfectly aware that danger is at -hand. Equally well do they feel that safety lies in concealment; and -while all the foraging party on the white floor are scuttling away into -dark corners, the fortunate dweller on the hearth stands motionless -beneath the shadow of the fire-irons; a picture of keen, intense -excitement, with antennæ quivering with alertness. On the clean floor a -careless girl has dropped a piece of flat coal, and on it beetles stand -rigidly. They are as conscious as we are that the shadow, and the colour -of the coal afford concealment, and we cannot doubt that they have -become black from their sense of the protection they thus enjoy. They do -not say, as Tom, the Water Baby, says, "I must be clean," but they know -they must be black, and black they are. - -There is, then, clearly an effort to assimilate in hue to their -surroundings, and the whole question is comparatively clear. - -Mr. Wallace, in commenting upon the butterfly (_Papilio nireus_)--which, -at the Cape, in its chrysalis state, copies the bright hues of the -vegetation upon which it passes its dormant phase--says that this is a -kind of natural colour photography; thus reducing the action to a mere -physical one. We might as well say the dun coat of the sportsman among -the brown heather was acquired mechanically. Moreover, Wallace -distinctly shows that when the larvæ are made to pupate on unnatural -colours, like sky-blue or vermilion, the pupæ do not mimic the colour. -There is no reason why "natural photography" should not copy this as -well as the greens, and browns, and yellows. But how easy the -explanation becomes when memory, the sense of need, and Butler's little -"dose of reason," are admitted! For ages the butterfly has been -acquainted with greens, and browns, and yellows, they are every day -experiences; but it has no acquaintance with aniline dyes, and therefore -cannot copy them. - -The moral of all this is that things become easy by repetition; that -without experience nothing can be done well, and that the course of -development is always in one direction, because the memory of the road -traversed is not forgotten. - - - [Illustration] - - - [3] Evolution, Old and New, p. 346. - [4] On a New Method of Expressing the Law of Specific Change. By A. - Tylor. - [5] Animals and Plants under Domestication, vol. ii., p. 350. - [6] Animals and Plants under Domestication, vol. ii., p. 370. - - - - - CHAPTER III. - - INTRODUCTORY SKETCH. - - -Natural science has shown us how the existing colouration of an animal -or plant can be laid hold of and modified in almost infinite ways under -the influence of natural or artificial evolution. - -It shows us, for example, how the early pink leaf-buds have been -modified into attractive flowers to ensure fertilisation; and it has -tracked this action through many of its details. It has explained the -rich hue of the bracts of _Bougainvillea_, in which the flowers -themselves are inconspicuous, and the coloured flower-stems in other -plants, as efforts to attract notice of the flower-frequenting insects. -It has explained how a blaze of colour is attained in some plants, as in -roses and lilies by large single flowers; how the same effect is -produced by a number of small flowers brought to the same plane by -gradually increasing flower-stalks, as in the elderberry, or by still -smaller flowers clustered into a head, as in daisies and sunflowers. - -It teaches us again how fruits have become highly coloured to lure -fruit-eating birds and mammals, and how many flowers are striped as -guides to the honey-bearing nectary. - -Entering more into detail, we are enabled to see how the weird -walking-stick and leaf-insects have attained their remarkable protective -resemblances, and how the East Indian leaf-butterflies are enabled to -deceive alike the birds that would fain devour them, and the naturalist -who would study them. Even the still more remarkable cases of protective -mimicry, in which one animal so closely mimics another as to derive all -the benefits that accrue to its protector, are made clear. - -All these and many other points have been deeply investigated, and are -now the common property of naturalists. - -But up to the present no one has attempted systematically to find out -the principles or laws which govern the distribution of colouration; -laws which underlie natural selection, and by which alone it can work. -Natural selection can show, for instance, how the lion has become almost -uniform in colour, while the leopard is spotted, and the tiger striped. -The lion living on the plains in open country is thus rendered less -conspicuous to his prey, the leopard delighting in forest glades is -hardly distinguishable among the changing lights and shadows that -flicker through the leaves, and the tiger lurking amid the jungle -simulates the banded shades of the cane-brake in his striped mantle. - -Beyond this, science has not yet gone; and it is our object to carry the -study of natural colouration still further: to show that the lion's -simple coat, the leopard's spots, and the tiger's stripes, are but -modifications of a deeper principle. - -Let us, as an easy and familiar example, study carefully the colouration -of a common tabby cat. First, we notice, it is darker on the back than -beneath, and this is an almost universal law. It would, indeed, be quite -universal among mammals but for some curious exceptions among monkeys -and a few other creatures of arboreal habits, which delight in hanging -from the branches in such a way as to expose their ventral surface to -the light. These apparent exceptions thus lead us to the first general -law, namely, that colouration is invariably most intense upon that -surface upon which the light falls. - -As in most cases the back of the animal is the most exposed, that is the -seat of intensest colour. But whenever any modification of position -exists, as for instance in the side-swimming fishes like the sole, the -upper side is dark and the lower light. - -The next point to notice in the cat is that from the neck, along the -back to the tail, is a dark stripe. This stripe is generally continued, -but slighter in character across the top of the skull; but it will be -seen clearly that at the neck the pattern changes, and the skull-pattern -is quite distinct from that on the body. - -From the central, or what we may call the back-bone stripe, bands pass -at a strong but varying angle, which we may call rib-stripes. - -Now examine the body carefully, and the pattern will be seen to change -at the shoulders and thighs, and also at each limb-joint. In fact, if -the cat be attentively remarked, it will clearly be seen that the -colouration or pattern is _regional_, and dependent upon the structure -of the cat. - -Now a cat is a vertebrate or backboned animal, possessing four limbs, -and if we had to describe its parts roughly, we should specify the head, -trunk, limbs and tail. Each of these regions has its own pattern or -decoration. The head is marked by a central line, on each side of which -are other irregular lines, or more frequently convoluted or twisted -spots. The trunk has its central axial backbone stripe and its lateral -rib-lines. The tail is ringed; the limbs have each particular stripes -and patches. Moreover, the limb-marks are largest at the shoulder and -hip-girdles, and decrease downwards, being smallest, or even wanting, on -the feet; and the changes take place at the joints. - -All this seems to have some general relation to the internal structure -of the animal. Such we believe to be the case; and this brings us to the -second great law of colouration, namely, that it is dependent upon the -anatomy of the animal. We may enunciate these two laws as follows:-- - - I. THE LAW OF EXPOSURE. Colouration is primarily dependent upon the - direct action of light, being always most intense upon that surface - upon which the light falls most directly. - - II. THE LAW OF STRUCTURE. Colouration, especially where - diversified, follows the chief lines of structure, and changes at - points, such as the joints, where function changes. - -It is the enunciation and illustration of these two laws that form the -subject of the present treatise. - -In the sequel we shall treat, in more or less detail, of each point as -it arises; but in order to render the argument clearer, this chapter is -devoted to a general sketch of my views. - -Of the first great law but little need be said here, as it is almost -self-evident, and has never been disputed. It is true not only of the -upper and under-sides of animals, but also of the covered and uncovered -parts or organs. - -For example, birds possess four kinds of feathers, of which one only, -the contour feathers, occur upon the surface and are exposed to the -light. It is in these alone that we find the tints and patterns that -render birds so strikingly beautiful, the underlying feathers being -invariably of a sober grey. Still further, many of the contour feathers -overlap, and the parts so overlapped, being removed from the light are -grey also, although the exposed part may be resplendent with the most -vivid metallic hues. A similar illustration can be found in most -butterflies and moths. The upper wing slightly overlaps the lower along -the lower margin, and although the entire surface of the upper wing is -covered with coloured scales, and the underwing apparently so as well, -it will be found that the thin unexposed margin is of an uniform grey, -and quite devoid of any pattern. - -The law of structure, on the other hand, is an entirely new idea, and -demands more detailed explanation. Speaking in the broadest sense, and -confining ourselves to the animal kingdom, animals fall naturally into -two great sections, or sub-kingdoms, marked by the possession or absence -of an internal bony skeleton. Those which possess this structure are -known as _Vertebrata_, or backboned animals, because the -vertebral-column or backbone is always present. The other section is -called the _Invertebrata_, or backboneless animals. - -Now, if we take the Vertebrata, we shall find that the system of -colouration, however modified, exhibits an unmistakably strong tendency -to assume a vertebral or axial character. Common observation confirms -this; and the dark stripes down the backs of horses, asses, cattle, -goats, etc., are familiar illustrations. The only great exception to -this law is in the case of birds, but here, again, the exception is more -apparent than real, as will be abundantly shown in the sequel. This -axial stripe is seen equally well in fishes and reptiles. - -For our present purpose we may again divide the vertebrates into limbed -and limbless. Wherever we find limbless animals, such as snakes, the -dorsal stripe is prominent, and has a strong tendency to break up into -vertebra-like markings. In the limbed animals, on the other hand, we -find the limbs strongly marked by pattern, and thus, in the higher forms -the system of colouration becomes axial and appendicular. - -As a striking test of the universality of this law we may take the -cephalopoda, as illustrated in the cuttle-fishes. These creatures are -generally considered to stand at the head of the Mollusca, and are -placed, in systems of classification, nearest to the Vertebrata; -indeed, they have even been considered to be the lowest type of -Vertebrates. This is owing to the possession of a hard axial organ, -occupying much the position of the backbone, and is the well-known -cuttle-bone. Now, these animals are peculiar amongst their class, from -possessing, very frequently, an axial stripe. We thus see clearly that -the dorsal stripe is directly related to the internal axial skeleton. - -Turning now to the invertebrata, we are at once struck with the entire -absence of the peculiar vertebrate plan of decoration; and find -ourselves face to face with several distinct plans. - -From a colouration point of view, we might readily divide the animal -kingdom into two classes, marked by the presence or absence of distinct -organs. The first of these includes all the animals except the -Protozoa--the lowest members of the animal kingdom--which are simply -masses of jelly-like protoplasm, without any distinct organs. - -Now, on our view, that colouration follows structure, we ought to find -an absence of decoration in this structureless group. This is what we -actually do find. The lowest Protozoa are entirely without any system of -colouring; being merely of uniform tint, generally of brown colour. As -if to place this fact beyond doubt, we find in the higher members a -tendency to organization in a pulsating vesicle, which constantly -retains the same position, and may, hence, be deemed an incipient organ. -Now, this vesicle is invariably tinged with a different hue from the -rest of the being. We seem, indeed, here to be brought into contact with -the first trace of colouration, and we find it to arise with the -commencement of organization, and to be actually applied to the -incipient organ itself. - -Ascending still higher in the scale, we come to distinctly organized -animals, known as the _Coelenterata_; of which familiar examples are -found in the jelly-fishes and sea anemonies. These animals are -characterized by the possession of distinct organs, are transparent, or -translucent, and the organs are arranged radially. - -No one can have failed to notice on our coasts, as the filmy -jelly-fishes float by, that the looped canals of the disc are delicately -tinted with violet; and closer examination will show the radiating -muscular bands as pellucid white lines; and the sense organs fringing -the umbrella are vividly black--the first trace of opaque colouration in -the animal kingdom. - -These animals were of yore united with the star-fishes and sea-urchins, -to form the sub-kingdom Radiata, because of their radiate structure. -Now, in all these creatures we find the system of colouration to be -radiate also. - -Passing to the old sub-kingdom Articulata, which includes the worms, -crabs, lobsters, insects, etc., we come to animals whose structure is -segmental; that is to say, the body is made up of a number of distinct -segments. Among these we find the law holds, rigidly that the -colouration is segmental also, as may be beautifully seen in lobsters -and caterpillars. - -Lastly, we have the Molluscs, which fall for our purpose into two -classes, the naked and the shelled. The naked molluscs are often most -exquisitely coloured, and the feathery gills that adorn many are -suffused with some of the most brilliant colours in nature. The shelled -molluscs differ from all other animals, in that the shell is a -secretion, almost as distinct from the animals as a house is from its -occupant. This shell is built up bit by bit along its margin by means of -a peculiar organ known as the mantle--its structure is marginate--its -decoration is marginate also. - -We have thus rapidly traversed the animal kingdom, and find that in all -cases the system of decoration follows the structural peculiarity of the -being decorated. Thus in the:-- - - Structureless protozoa there is no varying colouration. - Radiate animals--the system is radiate. - Segmented " " segmental. - Marginate " " marginal. - Vertebrate " " axial. - -We must now expound this great structural law in detail, and we shall -find that all the particular ornamentations in their various -modifications can be shown to arise from certain principles, namely-- - - 1. The principle of Emphasis, - 2. The " Repetition. - -The term _Emphasis_ has been selected to express the marking out or -distinguishing of important functional or structural regions by -ornament, either as form or colour. It is with colour alone that we have -to deal. - -Architects are familiar with the term emphasis, as applied to the -ornamentation of buildings. This ornamentation, they say, should -_emphasize_, point out, or make clear to the eye, the use or function -of the part emphasized. They recognise the fact that to give sublimity -and grace to a building, the ornamentation must be related to the -character of the building as a whole, and to its parts in particular. - -Thus in a tower whose object or function is to suggest height, the -principal lines of decoration must be perpendicular, while in the body -of a building such as a church, the chief lines must be horizontal, to -express the opposite sentiment. So, too, with individual parts. A banded -column, such as we see in Early English Gothic, looks weak and incapable -of supporting the superincumbent weight. It suggests the idea that the -shaft is bound up to strengthen it. On the other hand, the vertical -flutings of a Greek column, at once impress us with their function of -bearing vertical pressure and their power to sustain it. - -This principle is carried into colour in most of our useful arts. The -wheelwright instinctively lines out the rim and spokes and does not -cross them, feeling that the effect would be to suggest weakness. -Moreover, in all our handicraft work, the points and tips are emphasized -with colour. - -This principle seems to hold good throughout nature. It is not suggested -that the colouration is applied to important parts _in order to_ -emphasize them, but rather that being important parts, they have become -naturally the seats of most vivid colour. How this comes about we cannot -here discuss, but shall refer to it further on. - -It is owing to this pervading natural principle, that we find the -extreme points of quadrupeds so universally decorated. The tips of the -nose, ears and tail, and the feet also proclaim the fact, and the -decoration of the sense organs, even down to the dark spots around each -hair of a cat's feelers, are additional proofs. Look, for instance, at a -caterpillar with its breathing holes or spiracles along the sides, and -see how these points are selected as the seats of specialized colour, -eye-spots and stripes in every variety will be seen, all centred around -these important air-holes. - -This leads us to our second principle, that of repetition, which simply -illustrates the tendency to repeat similar markings in like areas. Thus -the spiracular marks are of the same character on each segment. - -The principle of repetition, however, goes further than this, and tends -to repeat the style of decoration upon allied parts. We see this -strongly in many caterpillars in which spiracular markings are -continued over the segments which lack spiracles; and it is probably -owing to this tendency that the rib-like markings on so many mammals are -continued beyond the ribs into the dorsal region. - -Upon these two principles the whole of the colouration of nature seems -to depend. But the plan is infinitely modified by natural selection, -otherwise the result would have been so patent as to need no -elucidation. - -Natural selection acts by suppressing, or developing, structurally -distributed colour. So far as our researches have gone, it seems most -probable that the fundamental or primitive colouration is arranged in -spots. These spots may expand into regular or irregular patches, or run -into stripes, of which many cases will be given in the sequel. Now, -natural selection may suppress certain spots, or lines, or expand them -into wide, uniform masses, or it may suppress some and repeat others. On -these simple principles the whole scheme of natural colouration can be -explained; and to do this is the object of the following pages. - -Into the origin of the colour sense it is not our province to enlarge; -but, it will reasonably be asked, How are these colours of use to the -creature decorated? The admiration of colour, the charm of landscape, is -the newest of human developments. Are we, then, to attribute to the -lower animals a discriminative power greater than most races of men -possess, and, if so, on the theory of evolution, how comes it that man -lost those very powers his remote ancestors possessed in so great -perfection? To these questions we will venture to reply. - -Firstly, then, it must be admitted that the higher animals do actually -possess this power; and no one will ever doubt it if he watches a common -hedge-sparrow hunting for caterpillars. To see this bird carefully -seeking the green species in a garden, and deliberately avoiding the -multitudes of highly coloured but nauseous larvæ on the currant bushes, -arduously examining every leaf and twig for the protected brown and -green larvæ which the keen eye of the naturalist detects only by close -observation; hardly deigning to look at the speckled beauties that are -feeding in decorated safety before his eyes, while his callow brood are -clamouring for food--to see this is to be assured for ever that birds -can, and do, discriminate colour perfectly. What is true of birds can be -shown to be true of other and lower types; and this leads us to a very -important conclusion--that colouration has been developed with the -evolution of the sense of sight. We can look back in fancy to the far -off ages, when no eye gazed upon the world, and we can imagine that then -colour in ornamental devices must have been absent, and a dreary -monotony of simple hues must have prevailed. - -With the evolution of sight it might be of importance that even the -sightless animals should be coloured; and in this way we can account for -the decoration of coral polyps, and other animals that have no eyes; -just as we find no difficulty in understanding the colouration of -flowers. - -Colour, in fact, so far as external nature is concerned, is all in all -to the lower animals. By its means prey is discovered, or foes escaped. -But in the case of man quite a different state of things exists. The -lower animals can only be modified and adapted to their surroundings by -the direct influence of nature. Man, on the other hand, can utilise the -forces of nature to his ends. He does not need to steal close to his -prey--he possesses missiles. His arm, in reality, is bounded, not by his -finger tips, but by the distance to which he can send his bolts. He is -not so directly dependent upon nature; and, as his mental powers -increase, his dependence lessens, and in this way--the æsthetic -principle not yet being awakened--we can understand how his colour -sense, for want of practice, decayed, to be reawakened in these our -times, with a vividness and power as unequalled as is his mastery over -nature--the master of his ancestors. - - - [Illustration] - - - - - CHAPTER IV. - - COLOUR, ITS NATURE AND RECOGNITION. - - -This chapter will be devoted to a slight sketch of the nature of light -and colour, and to proofs that niceties of colour are distinguished by -animals. - -First, as to the nature of light and colour. Colour is essentially the -effect of different kinds of vibrations upon certain nerves. Without -such nerves, light can produce no luminous effect whatever; and to a -world of blind creatures, there would be neither light nor colour, for -as we have said, light and colour are not material things, but are the -peculiar results or effects of vibrations of different size and -velocity. - -These effects are due to the impact of minute undulations or waves, -which stream from luminous objects, the chief of which is the sun. These -waves are of extreme smallness, the longest being only 226 -_ten-millionths_ of an inch from crest to crest. The tiny billows roll -outwards and onwards from their source at inconceivable velocities, -their mean speed being 185,000 miles in a second. Could we see these -light billows themselves and count them as they rolled by, 450 billions -(450,000,000,000,000) would pass in a single second, and as the last -ranged alongside us, the first would be 185,000 miles away. We are not -able, however, to see the waves themselves, for the ocean whose -vibrations they are, is composed of matter infinitely more transparent -than air, and infinitely less dense. Light, then, be it clearly -understood, is not the ethereal billows or waves themselves, but only -the effect they produce on falling upon a peculiar kind of matter called -the optic nerve. When the same vibrations fall upon a photographic -sensitive film, another effect--chemical action--is produced: when they -fall upon other matter, heat is the result. Thus heat, light and -chemical action are but phases, expressions, effects or results of the -different influences of waves upon different kinds of matter. The same -waves or billows will affect the eye itself as light, the ordinary -nerves as warmth, and the skin as chemical action, in tanning it. - -Though we cannot see these waves with the material eye, they are visible -indeed to the mental eye; and are as amenable to experimental research -as the mightiest waves of the sea. Still, to render this subject -clearer, we will use the analogy of sound. A musical note, we all know, -is the effect upon our ears of regularly recurring vibrations. A -pianoforte wire emits a given note, or in other words, vibrates at a -certain and constant rate. These vibrations are taken up by the air, and -by it communicated to the ear, and the sensation of sound is produced. -Here we see the wire impressing its motion on the air, and the air -communicating its motion to the ear; but if another wire similar in all -respects is near, it will also be set in motion, and emit its note; and -so will any other body that can vibrate in unison. Further, the note of -the pianoforte string is not a simple tone, but superposed, as it were, -upon the fundamental note, are a series of higher tones, called -harmonics, which give richness. Now, a ray of sun-light may be likened -to such a note; it consists not of waves all of a certain length or -velocity, but of numbers of waves of different lengths and speed. When -all these fall upon the eye, the sensation of white light is produced, -white light being the compound effect, like the richness of the tone of -the wire and its harmonies; or we may look upon it as a luminous chord. -When light strikes on any body, part or all is reflected to the eye. If -all the waves are thus reflected equally, the result is whiteness. If -only a part is reflected, the effect is colour, the tint depending upon -the particular waves reflected. If none of the waves are reflected, the -result is blackness. - -Colour, then, depends upon the nature of the body reflecting light. The -exact nature of the action of the body upon the light is not known, but -depends most probably upon the molecular condition of the surface. -Bodies which allow the light to pass through them, are in like manner -coloured according to the waves they allow to pass. - -We find in nature, however, a somewhat different class of colour, -namely, the iridescent tints, like mother of pearl or shot silk, which -give splendour to such butterflies, as some Morphos and the Purple -Emperor. These are called diffraction colours, and are caused by minute -lines upon the reflecting surface, or by thin transparent films. These -lines or films must be so minute that the tiny light waves are broken up -among them, and are hence reflected irregularly to the eye. - -Dr. Hagen has divided the colours of insects into two classes, the -epidermal and hypodermal. The epidermal colours are produced in the -external layer or epidermis which is comparatively dry, and are -persistent, and do not alter after death. Of this nature are the -metallic tints of blue, green, bronze, gold and silver, and the dead -blacks and browns, and some of the reds. The hypodermal colours are -formed in the moister cells underlying the epidermis, and on the drying -up of the specimen fade, as might be expected. They show through the -epidermis, which is more or less transparent. These colours are often -brighter and lighter in hue than the epidermal; and such are most of the -blues, and greens, and yellow, milk white, orange, and the numerous -intermediate shades. These colours are sometimes changeable by voluntary -act, and the varying tints of the chameleon and many fishes are of this -character. - -In this connection, Dr. Hagen remarks, that probably all mimetic colours -are hypodermal. The importance of this suggestion will be seen at once, -for it necessitates a certain consciousness or knowledge on the part of -the mimicker, which we have shown, seems to be an essential factor in -the theory of colouration. - -This author further says, that "the pattern is not the product of an -accidental circumstance, but apparently the product of a certain law, or -rather the consequence of certain actions or wants in the interior of -the animal and in its development." - -This remarkable paper, to which our attention was called after our work -was nearly completed, is the only record we have been able to find which -recognises a law of colouration. - -From what has been said of the nature of light, and the physical origin -of colour, we see that to produce any distinct tint such as red, yellow, -green, or blue, a definite physical structure must be formed, capable of -reflecting certain rays of the same nature and absorbing others. Hence, -whenever we see any distinct colour, we may be sure that a very -considerable development in a certain direction has taken place. This -is a most important conclusion, though not very obvious at first sight. -Still, when we bear in mind the numbers of light waves of different -lengths, and know that if these are reflected irregularly, we get only -mixed tints such as indefinite browns; we can at once see how, in the -case of such objects as tree trunks, and, still more, in inanimate -things like rocks and soils, these, so-to-say, undifferentiated hues are -just what we might expect to prevail, and that when definite colours are -produced, it of necessity implies an effort of some sort. Now, if this -be true of such tints as red and blue, how much more must it be the case -with black and white, in which all the rays are absorbed or all -reflected? These imply an even stronger effort, and _a priori_ reasoning -would suggest that where they occur, they have been developed for -important purposes by what may be termed a supreme effort. Consequently, -we find them far less common than the others; and it is a most singular -fact that in mimetic insects, these are the colours that are most -frequently made use of. It would almost seem as if a double struggle had -gone on: first, the efforts which resulted in the protective colouring -of the mimicked species, and then a more severe, because necessarily -more rapid, struggle on the part of the mimicker. - -Yet another point in this connection. If this idea be correct, it -follows that a uniformly coloured flower or animal must be of extreme -rarity, since it necessitates not merely the entire suppression of the -tendency to emphasize important regions in colour, but also the -adjustment of all the varying parts of the organism to one uniform -molecular condition, which enables it to absorb all but a certain -closely related series of light waves no matter how varied the functions -of the parts. Now, such "self-coloured" species, as florists would call -them, are not only rare, but, as all horticulturists know, are extremely -difficult to produce. When a pansy grower, for instance, sets to work to -produce a self-coloured flower--say a white pansy without a dark -eye--his difficulties seem insurmountable. And, in truth, this result -has never been quite obtained; for he has to fight against every natural -tendency of the plant to mark out its corolla-tube in colour, and when -this is overcome, to still restrain it, so as to keep it within those -limits which alone allow it to reflect the proper waves of light. - - [Illustration: Plate I. - KALLIMA INACHUS.] - -The production of black and white, then, being the acme of colour -production, we should expect to find these tints largely used for -very special purposes. Such is actually the case. The sense organs are -frequently picked out with black, as witness the noses of dogs, the tips -of their ears, the insertion of their vibrissæ, or whiskers, and so on; -and white is the most usual warning or distinctive colour, as we see in -the white stripes of the badger and skunk, the white spots of deer, and -the white tail of the rabbit. - -Colour, then, as expressed in definite tints and patterns, is no -accident; for although, as Wallace has well said, "colour is the normal -character," yet we think that this colour would, if unrestrained and -undirected, be indefinite, and could not produce definite tints, nor the -more complicated phenomenon of patterns, in which definite hues are not -merely confined to definite tracts, but so frequently contrasted in the -most exquisite manner. As we write, the beautiful Red Admiral (_V. -atalanta_) is sporting in the garden; and who can view its glossy black -velvet coat, barred with vividest crimson, and picked out with purest -snow white, and doubt for an instant that its robe is not merely the -product of law, but the supreme effort of an important law? Mark the -habits of this lovely insect. See how proudly it displays its rich -decorations; sitting with expanded wings on the branch of a tree, gently -vibrating them as it basks in the bright sunshine; and you know, once -and for all, that the object of that colour is display. But softly--we -have moved too rudely, and it is alarmed. The wings close, and where is -its beauty now? Hidden by the sombre specklings of its under wings. See, -it has pitched upon a slender twig, and notice how instinctively (shall -we say?) it arranges itself in the line of the branch: if it sat athwart -it would be prominent, but as it sits there motionless it is not only -almost invisible, _but it knows it_; for you can pick it up in your -hands, as we have done scores of times. It is not enough, if we would -know nature, to study it in cabinets. There is too much of this dry-bone -work in existence. The object of nature is _life_; and only in living -beings can we learn how and why they fulfil their ends. - -Here, in this common British butterfly, we have the whole problem set -before us--vivid colour, the result of intense and long continued -effort; grand display, the object of that colour; dusky, indefinite -colour, for concealment; and the "instinctive" pose, to make that -protective colour profitable. The insect _knows_ all this in some way. -How it knows we must now endeavour to find out. - -In attacking this problem we must ask ourselves, What are the purposes -that colouration, and, especially, decoration, can alone subserve? We -can only conceive it of use in three ways: first, as protection from its -enemies; second, as concealment from its prey; third, as distinctive for -its fellows. To the third class may be added a sub-class--attractiveness -to the opposite sex. - -The first necessity would seem to be distinctness of species; for, -unless each species were separately marked, it would be difficult for -the sexes to discriminate mates of their own kind, in many instances; -and this is, doubtless, the reason why species _are_ differently -coloured. - -But protective resemblance, as in _Kallima_,[7] the Leaf-butterfly, and -mimicry, as in _D. niavius_ and _P. merope_,[8] sometimes so hide the -specific characters that this process seems antagonistic to the prime -reason for colouration, by rendering species less distinct. Now, -doubtless, protective colouring could not have been so wonderfully -developed _if the organ of sight were the only means of recognition_. -But it is not. Animals possess other organs of recognition, of which, as -everyone knows, smell is one of the most potent. A dog may have -forgotten a face after years of absence, but, once his cold nose has -touched your hand, the pleased whine and tail-wagging of recognition, -tells of awakened memories. Even with ourselves, dulled as our senses -are, the odour of the first spring violet calls up the past; as words -and scenes can never do. What country-bred child forgets the strange -smell of the city he first visits? and how vividly the scene is recalled -in after years by a repetition of that odour! - -But insects, and, it may be, many other creatures, possess sense organs -whose nature we know not. The functions of the antennæ and of various -organs in the wings, are unknown; and none can explain the charm by -which the female Kentish Glory, or Oak Egger moths lure their mates. You -may collect assiduously, using every seduction in sugars and lanterns, -only to find how rare are these insects; but if fortune grant you a -virgin female, and you cage her up, though no eye can pierce her prison -walls, and though she be silent as the oracles, she will, in some -mysterious way, attract lovers; not singly, but by the dozen; not one -now and another in an hour, but in eager flocks. Many butterflies -possess peculiar scent-pouches on their wings, and one of these, a -_Danais_, is mimicked by several species. It is the possession of these -additional powers of recognition that leaves colouration free to run to -the extreme of protective vagary, when the species is hard pressed in -the struggle for life. - - [Illustration: Plate II. - MIMICRY.] - -Nevertheless, though animals have other means of recognition, the -distinctive markings are, without doubt, the prime means of knowledge. -Who, that has seen a peacock spread his glorious plumes like a radiant -glory, can doubt its fascination? Who, that has wandered in America, and -watched a male humming-bird pirouetting and descending in graceful -spirals, its whole body throbbing with ecstasy of love and jealousy, can -doubt? Who can even read of the Australian bower-bird, lowliest and -first of virtuosi, decorating his love-bower with shells and flowers, -and shining stones, running in and out with evident delight, and -re-arranging his treasures, as a collector does his gems, and not be -certain that here, at least, we have the keenest appreciation, not only -of colour, but of beauty--a far higher sense? - -It has been said that butterflies must be nearly blind, because they -seldom fly directly over a wall, but feel their way up with airy -touches. Yet every fact of nature contradicts the supposition. Why have -plants their tinted flowers, but to entice the insects there? Why are -night-blooming flowers white, or pale yellows and pinks, but to render -them conspicuous? Why are so many flowers striped in the direction of -the nectary, but to point the painted way to the honey-treasures below? -The whole scheme of evolution, the whole of the new revelation of the -meanings of nature, becomes a dead letter if insects cannot appreciate -the hues of flowers. The bee confines himself as much as possible to one -species of flower at a time, and this, too, shows that it must be able -to distinguish them with ease. We may, then, take it as proven that the -power of discriminating colours is possessed by the lower animals. - - - [Illustration] - - - [7] Pl. I., Figs 1-3. - [8] Pl. II., Figs. 1-3. - - - - - CHAPTER V. - - THE COLOUR SENSE. - - -The previous considerations lead us, naturally, to enquire in what -manner the sense of colour is perceived. - -In thinking over this obscure subject, the opinion has steadily gathered -strength that form and colour are closely allied; for form is essential -to pattern; and colour without pattern, that is to say, colour -indefinitely marked, or distributed, is hardly decoration at all, in the -sense we are using the term. That many animals possess the power of -discriminating form is certain. Deformed or monstrous forms are driven -from the herds and packs of such social animals as cattle, deer, and -hogs, and maimed individuals are destroyed. Similar facts have been -noticed in the case of birds. This shows a power of recognising any -departure from the standard of form, just as the remorseless destruction -of abnormally coloured birds, such as white or piebald rooks and -blackbirds, by their fellows, is proof of the recognition and dislike of -a departure from normal colouring. Authentic anecdotes of dogs -recognising their masters' portraits are on record; and in West Suffolk, -of late years, a zinc, homely representation of a cat has been found -useful in protecting garden produce from the ravages of birds. In this -latter case the birds soon found out the innocent nature of the fraud, -for we have noticed, after a fortnight, the amusing sight of sparrows -cleaning their beaks on the whilom object of terror. Many fish are -deceived with artificial bait, as the pike, with silvered minnows; the -salmon, and trout, with artificial flies; the glitter of the spoon-bait -is often most attractive; and mackerel take greedily to bits of red -flannel. Bees sometimes mistake artificial for real flowers; and both -they and butterflies have been known to seek vainly for nourishment -from the gaudy painted flowers on cottage wall-papers. Sir John Lubbock -has demonstrated the existence of a colour sense in bees, wasps, and -ants; and the great fact that flowers are lures for insects proves -beyond the power of doubt that these creatures have a very strong -faculty for perceiving colour. - -The pale yellows and white of night-flowering plants render them -conspicuous to the flower-haunting moths; and no one who has ever used -an entomologist's lantern, or watched a daddy-long-legs (_Tipula_) -dancing madly round a candle, can fail to see that intense excitement is -caused by the flame. In the dim shades of night the faint light of the -flowers tells the insects of the land of plenty, and the stimulus thus -excited is multiplied into a frenzy by the glow of a lamp, which, -doubtless, seems to insect eyes the promise of a feast that shall -transcend that of ordinary flowers, as a Lord Mayor's feast transcends a -homely crust of bread and cheese. - -We take it, then, as proven that the colour sense does exist, at least, -in all creatures possessing eyes. But there are myriads of animals -revelling in bright tints; such as the jelly-fishes and anemones, and -even lower organisms, in which eyes are either entirely wanting or are -mere eye-specks, as will be explained in the sequel. How these behave -with regard to colour is a question that may, with propriety, be asked -of science, but to which, at present, we can give no very definite -reply. Still, certain modern researches open to us a prospect of being -able, eventually, to decide even this obscure problem. - -The question, however, is not a simple one, but involves two distinct -principles; firstly, as to how colour affects the animal coloured, and, -secondly, how it affects other animals. In other words, How does colour -affect the sensibility of its possessor? and how does it affect the -sense organs of others? - -To endeavour to answer the first question we must start with the lowest -forms of life, and their receptivity to the action of light; for, as -colour is only a differentiation of ordinary so-called white light, we -might _a priori_ expect that animals would show sensibility to light as -distinguished from darkness, before they had the power of discriminating -between different kinds of light. - -This appears to be the case, for Engelmann has shown[9] that many of -the lowest forms of life, which are almost mere specks of protoplasm, -are influenced by light, some seeking and others shunning it. He found, -too, that in the case of _Euglena viridis_ it would seek the light only -if it "were allowed to fall upon the anterior part of the body. Here -there is a pigment spot; but careful experiment showed that this was not -the point most sensitive to light, a colourless and transparent area of -protoplasm lying in front of it being found to be so." Commenting upon -this Romanes observes, "it is doubtful whether this pigment spot is or -is not to be regarded as an exceedingly primitive organ of special -sense." Haeckel has also made observations upon those lowest forms of -life, which, being simply protoplasm without the slightest trace of -organization, not even possessing a nucleus, form his division -_Protista_, occupying the no-man's-land between the animal and vegetable -kingdoms. He finds that "already among the microscopic Protista there -are some that love light, and some that love darkness rather than light. -Many seem also to have smell and taste, for they select their food with -great care.... Here, also, we are met by the weighty fact that -sense-function is possible without sense organs, without nerves. In -place of these, sensitiveness is resident in that wondrous, -structureless, albuminous substance, which, under the name of -protoplasm, or organic formative material, is known as the general and -essential basis of all the phenomena of life."[10] - -Now, whether Romanes be correct in doubting whether the pigment-spot in -Euglena is a sense organ or not, matters little to our present enquiry, -but it certainly does seem that the spot, _with its accompanying clear -space_, looks like such an organ. And when we are further told that -after careful experiment it is found that _Euglena viridis_ prefers blue -to all the colours of the spectrum, the fundamental fact seems to be -established that even as low down as this the different parts of the -spectrum affect differently the body of creatures very nearly at the -bottom of the animal scale. This implies a certain selection of colour, -and, equally, an abstention from other colours. - -It is not part of our scheme, however, to follow out in detail the -development of the organs of special sense, and the reader must be -referred to the various works of Mr. Romanes, who has worked long and -successfully at this and kindred problems. Suffice it to say that in -this and other cases he has been led to adopt the theory of inherited -memory, though not, as we believe, in the fulness with which it must -ultimately be acquired. - -This, however, seems certain, that the development, not only of the -sense organs, but of organs in general--that is, the setting aside of -certain portions for the performance of special duties, and the -modifications of those parts in relation to their special duties, is -closely related to the activity of the organism. Thus, we find in those -animals, like some of the Coelenterata, which pass some portion of their -existence as free-swimming beings, and the remainder in a stationary or -sessile condition, that the former state is the most highly organized. -This is shown to a very remarkable degree in the Sea Squirts -(Ascidians), a class of animals that are generally grouped with the -lower Mollusca, but which Prof. Ray Lankester puts at the base of the -Vertebrata. - -These animals are either solitary or social, fixed or free; but even -when free, have little or no power of locomotion, simply floating in the -sea. Their embryos are, however, free-swimming, and some of the most -interesting beings in nature. Some are marvellously like young tadpoles, -and possess some of the distinctive peculiarities of the Vertebrata. -Thus, the body is divided into a head and body, or tail, as in tadpoles. -The head contains a large nerve centre, corresponding with the brain, -which is produced backwards into a chord, corresponding to the spinal -chord. In the head, sense organs are clearly distinguishable; there is a -well-marked eye, an equally clear ear, and a less clearly marked -olfactory organ. Besides this, the spinal-cord is supported below by a -rod-like structure, called the notochord. In the vertebrate embryo this -structure always precedes the development of the true vertebral column, -and in the lowest forms is persistent through life. - -We have thus, in the ascidian larva, a form which, if permanent, would -most certainly entitle it to a place in the vertebrate sub-kingdom. It -is now an active free-swimming creature, but as maturity approaches it -becomes fixed, or floating, and all this pre-figurement of a high -destiny is annulled. The tail, with its nervous cord and notochord -atrophies, and in the fixed forms, not only do the sense organs pass -away, but the entire nervous system is reduced to a single ganglion, and -the creature becomes little more than an animated stomach. It is, as Ray -Lankester has pointed out, a case of degeneration. In the floating -forms, which still possess a certain power of locomotion, this process -is not carried to such extremes, and the eye is left. - -Now, cases of this kind are important as illustrating the direct -connection between an active life and advancement; and they also add -indirectly to the view Wallace takes of colouration, namely, that the -most brilliant colour is generally applied to the most highly modified -parts, and is brightest in the seasons of greatest activity. - -But they have a higher meaning also, for they may point us to the prime -cause of the divergence of the animal and vegetable kingdoms. In -thinking over this matter, one of us ventured to suggest that probably -the reason why animals dominate the world, and not plants, is, that -plants are, as a rule, stationary, and animals lead an active existence. -We can look back to the period prior to the divergence of living -protoplasm into the two kingdoms. Two courses only were open to it, -either to stay at home, and take what came in its way, or to travel, and -seek what was required. The stay-at-homes became plants, and the -gad-abouts animals. In a letter it was thus put; "It is a truly strange -fact that a free-swimming, sense-organ-bearing animal should degenerate -into a fixed feeding and breeding machine. It seems to me that the power -of locomotion is a _sine qua non_ for active development of type, as it -necessarily sharpens the wits by bringing fresh experiences and -unlooked-for adventures to the creature. I almost think, and this, I -believe may be a great fundamental fact, that the only reason why -animals rule the world instead of plants is that plants elected to stay -at home, and animals did not. They had equal chances. Both start as -active elements; the one camps down, and the other looks about him." - -Talking over this question with Mr. Butler, he astonished the writer by -quoting from his work, "Alps and Sanctuaries" (p. 196), the following -passage:-- - - "The question of whether it is better to abide quiet, and take - advantage of opportunities that come, or to go farther afield in - search of them, is one of the oldest which living beings have to - deal with. It was on this that the first great schism or heresy - arose in what was heretofore the catholic faith of protoplasm. The - schism still lasts, and has resulted in two great sects--animals - and plants. The opinion that it is better to go in search of prey - is formulated in animals; the other--that it is better, on the - whole, to stay at home, and profit by what comes--in plants. Some - intermediate forms still record to us the long struggle during - which the schism was not yet complete. - - "If I may be pardoned for pursuing this digression further, I would - say that it is the plants, and not we, who are the heretics. There - can be no question about this; we are perfectly justified, - therefore, in devouring them. Ours is the original and orthodox - belief, for protoplasm is much more animal than vegetable. It is - much more true to say that plants have descended from animals than - animals from plants. Nevertheless, like many other heretics, plants - have thriven very fairly well. There are a great many of them, and, - as regards beauty, if not wit--of a limited kind, indeed, but still - wit--it is hard to say that the animal kingdom has the advantage. - The views of plants are sadly narrow; all dissenters are - narrow-minded; but within their own bounds they know the details of - their business sufficiently well--as well as though they kept the - most nicely-balanced system of accounts to show them their - position. They are eaten, it is true; to eat them is our intolerant - and bigoted way of trying to convert them: eating is only a violent - mode of proselytizing, or converting; and we do convert them--to - good animal substance of our own way of thinking. If we have had no - trouble we say they have 'agreed' with us; if we have been unable - to make them see things from our point of view, we say they - 'disagree' with us, and avoid being on more than distant terms with - them for the future. If we have helped ourselves to too much, we - say we have got more than we can 'manage.' And an animal is no - sooner dead than a plant will convert it back again. It is obvious, - however, that no schism could have been so long successful without - having a good deal to say for itself. - - "Neither party has been quite consistent. Whoever is or can be? - Every extreme--every opinion carried to its logical end will prove - to be an absurdity. Plants throw out roots and boughs and leaves: - this is a kind of locomotion; and as Dr. Erasmus Darwin long since - pointed out, they do sometimes approach nearly to what is called - travelling; a man of consistent character will never look at a - bough, a root, or a tendril, without regarding it as a melancholy - and unprincipled compromise. On the other hand, many animals are - sessile; and some singularly successful genera, as spiders, are in - the main liers-in-wait." - -This exquisitively written passage the writer was quite unaware of -having read, though he possessed and had perused the work quoted, nor -can he understand how such an admirable exposition could have escaped -notice. Had he read it: had he assimilated it so thoroughly as to be -unconscious of its existence; is this a case of rapid growth of -automatism? He cannot say. - -To return to the main point, it would seem that specialization is -directly proportionate to activity, and when we compare the infinitely -diverse organization of the animal with the comparative simplicity of -the vegetable world, this conclusion seems to be inevitable. - - - [Illustration] - - - [9] Pflüger's Archiv. f. d. ges. Phys. Bd. xxix, 1882, quoted by - Romanes. Mental Evolution, p. 80, 1883. _Op. cit._ p. 80. - [10] Quoted by Romanes, _op. cit._ p. 81. - - - - - CHAPTER VI. - - SPOTS AND STRIPES. - - -Bearing in mind the great tendency to repetition and symmetry of marking -we have shown to exist, it becomes an interesting question to work out -the origin of the peculiar spots, stripes, loops and patches which are -so prevalent in nature. The exquisite eye-spots of the argus pheasant, -the peacock, and many butterflies and moths have long excited admiration -and scientific curiosity, and have been the subject of investigation by -Darwin,[11] the Rev. H. H. Higgins,[12] Weismann,[13] and others, Darwin -having paid especial attention to the subject. - -His careful analysis of the ocelli or eye-spots in the Argus pheasant -and peacock have led him to conclude that they are peculiar -modifications of the bars of colour as shown by his drawings. Our own -opinion, founded upon a long series of observations, is that this is not -the whole case, but that, in the first place, bars are the result of the -coalescence of spots. It is not pretended that a bar of colour is the -result of the running together of a series of perfect ocelli like those -in the so-called tail of the peacock, but merely that spots of colour -are the normal primitive commencement of colouring, and that these spots -may be developed on the one hand into ocelli or eye-spots, and on the -other into bars or even into great blotches of a uniform tint, covering -large surfaces. - -Let us first take the cases of abnormal marking as shown in disease. An -ordinary rash, as in measles, begins as a set of minute red spots, and -the same is the case with small pox, the pustules of which sometimes run -together, and becoming confluent form bars, which again enlarging meet -and produce a blotch or area abnormally marked. It was these well-known -facts that induced us to re-examine this question. Colouration and -discolouration arise from the presence or absence of pigment in cells, -and thus having, as it were independent sources, we should expect colour -first to appear in spots. We have already stated, and shall more fully -show in the sequel, how colouration follows structure, and would here -merely remark that it seems as if any peculiarity of structure, or -intensified function modifying structure, has a direct tendency to -influence colour. Thus in the disease known as frontal herpes, as -pointed out to us by Mr. Bland Sutton, of the Middlesex Hospital, the -affection is characterized by an eruption on the skin corresponding -exactly to the distribution of the ophthalmic division of the fifth -cranial nerve, mapping out all its little branches, even to the one -which goes to the tip of the nose. Mr. Hutchinson, F.R.S., the President -of the Pathological Society, who first described this disease, has -favoured us with another striking illustration of the regional -distribution of the colour effects of herpes. In this case decolouration -has taken place. The patient was a Hindoo, and upon his brown skin the -pigment has been destroyed in the arm along the course of the ulnar -nerve, with its branches along both sides of one finger and the half of -another. In the leg the sciatic and saphenous nerves are partly mapped -out, giving to the patient the appearance of an anatomical diagram.[14] - -In these cases we have three very important facts determined. First the -broad fact that decolouration and colouration in some cases certainly -follow structure; second, that the effect begins as spots; thirdly, that -the spots eventually coalesce into bands and blotches. - -In birds and insects we have the best means of studying these phenomena, -and we will now proceed to illustrate the case more fully. The facts -seem to justify us in considering that starting with a spot we may -obtain, according to the development, either an ocellus, a stripe or -bar, or a blotch, and that between, these may have any number of -intermediate varieties. - - * * * * * - -Among the butterflies we have numerous examples of the development from -spots, as illustrated in plates. A good example is seen in our common -English Brimstone (_Gonepteryx rhamni_) Fig. 2, Plate III. In this -insect the male (figured) is of a uniform sulphur yellow, with a rich -orange spot in the cell of each wing; the female is much paler in -colour, and spotted similarly. In an allied continental species (_G. -Cleopatra_) Fig. 1, Plate III., the female is like that of _rhamni_ only -larger; but the male, instead of having an orange spot in the fore-wing, -has nearly the whole of the wing suffused with orange, only the margins, -and the lower wings showing the sulphur ground-tint like that of -_rhamni_. Intermediate forms between these two species are known. In a -case like this we can hardly resist the conclusion that the discoidal -spot has spread over the fore-wing and become a blotch, and in some -English varieties of _rhamni_ we actually find the spot drawn out into a -streak. - - [Illustration: Plate III. - BUTTERFLIES.] - -The family of _Pieridæ_, or whites, again afford us admirable examples -of the development of spots. The prevailing colours are white, black and -yellow: green _appears_ to occur in the Orange-tips (_Anthocaris_), but -it is only the optical effect of a mixture of yellow and grey or black -scales. The species are very variable, as a rule, and hence of -importance to us; and there are many intermediate species on the -continent and elsewhere which render the group a most interesting study. - -The wood white (_Leucophasia sinapis_) Fig. 1, Plate IV., is a pure -white species with an almost square dusky tip to the fore-wings of the -male. In the female this tip is very indistinct or wanting, Fig. 4, -Plate IV. In the variety _Diniensis_, Fig. 2, Plate IV., this square tip -appears as a round spot. - -The Orange-tips, of which we have only one species in Britain -(_Anthocaris cardamines_) belongs to a closely allied genus, as does -also the continental genus Zegris. The male Orange-tip (_A. cardamines_) -is white with a dark grey or black tip, and a black discoidal spot. A -patch of brilliant orange extends from the dark tip to just beyond the -discoidal spots. In the female this is wanting, but the dark tip and -spot are larger than in the male. - -Let us first study the dark tip. In _L. sinapis_ we have seen that it -extends right to the margin of the wing in the male, but in the female -is reduced to a dusky spot away from the margin. In _A. cardamines_ the -margin is not coloured quite up to the edge, but a row of tiny white -spots, like a fringe of seed pearls, occupies the inter-spaces of the -veins. On the underside these white spots are prolonged into short bars, -see Plate IV. In the continental species _A. belemia_ we see the dark -tip to be in a very elementary condition, being little more than an -irregular band formed of united spots, there being as much white as -black in the tip, Fig. 5, Plate IV. In _A. belia_, Fig. 6, Plate IV., -the black tip is more developed, and in the variety _simplonia_ still -more so, Fig. 7, Plate IV. We here see pretty clearly that this dark tip -has been developed by the confluence of irregular spots. - -Turning now to the discoidal spot we shall observe a similar -development. Thus in:-- - - _A. cardamines_, male, it is small and perfect. - Do. female, " larger " - _A. belemia_ " large " - _A. belia_ " large with white centre. - Do. _v. simplonia_ " small and perfect. - [15]_A. eupheno_, female, " nearly perfect. - Do. male, " a band. - -We here find two distinct types of variation. In _A. belia_ we have a -tendency to form an ocellus, and in _A. eupheno_ the spot of the female -is expanded into a band in the male. - -The orange flush again offers us a similar case; and with regard to this -colour we may remark that it seems to be itself a development from the -white ground-colour of the family in the direction of the red end of the -spectrum. Thus in the Black-veined white (_Aporia cratægi_) we have both -the upper and under surfaces of the typical cream-white, for there is no -pure white in the family. In the true whites the under surface of the -hind-wings is lemon-yellow, in the female of _A. eupheno_ the ground of -the upper surface is faint lemon-yellow, and in the male this colour is -well-developed. The rich orange, confined to a spot in _G. rhamni_ -becomes a flush in _G. Cleopatra_, and a vivid tip in _A. cardamines_. -These changes are all developments from the cream white, and may be -imitated accurately by adding more and more red to the primitive yellow, -as the artist actually did in drawing the plate. - - [Illustration: Plate IV. - SPOTS AND STRIPES.] - -In _A. cardamines_ the orange flush has overflowed the discoidal spot, -as it were, in the male, and is absent in the female. But in _A. -eupheno_ we have an intermediate state, for as the figures show, in the -female, Fig. 8, the orange tip only extends half-way to the discoidal -spot, and in the male it reaches it. Moreover it is to be noticed that -the flow of colour, to continue the simile, is unchecked by the spot in -_cardamines_, but where the spot has expanded to a bar in _eupheno_ -it has dammed the colour up and ponded it between bar and tip. An -exactly intermediate case between these two species is seen in _A. -euphemoides_, Fig. 10, Plate IV., in which the spot is elongated, and -dribbles off into an irregular band, into which the orange has trickled, -as water trickles through imperfect fascines. This series of -illustrations might be repeated in almost any group of butterflies, but -sufficient has been said to show how spots can spread into patches, -either by the spreading of one or by the coalescence of several. - -We will now take an illustration of the formation of stripes or bars -from spots, and in doing so must call attention to the rarity of true -stripes in butterflies. By a true stripe I mean one that has even edges, -that is, whose sides are uninfluenced by structure. In all our British -species such as _P. machaon_, _M. artemis_, _M. athalia_, _V. atalanta_, -_L. sibilla_, _A. iris_, and some of the Browns, Frittilaries and -Hair-streaks, which can alone be said to be striped, the bands are -clearly nothing more than spots which have spread up to the costæ, and -still retain traces of their origin either in the different hue of the -costæ which intersect them, or in curved edges corresponding with the -interspaces of the costæ. This in itself is sufficient to indicate their -origin. But in many foreign species true bands are found, though they -are by no means common. Illustrations are given in Plate IV., of two -Swallow-tails, _Papilio machaon_, Fig. 11, and _P. podalirius_, Fig. 12, -in which the development of a stripe can readily be seen. - -In _machaon_ the dark band inside the marginal semi-lunar spots of the -fore-wings retain traces of their spot-origin in the speckled character -of the costal interspaces, and in the curved outlines of those parts. In -_podalirius_ the semi-lunar spots have coalesced into a stripe, only -showing its spot-origin in the black markings of the intersecting costæ; -and the black band has become a true stripe, with plain edges. Had only -such forms as this been preserved, the origin of the spots would have -been lost to view. - -It may, however, be said, though I think not with justice, that we ought -not to take two species, however closely allied, to illustrate such a -point. But very good examples can be found in the same species. A common -German butterfly, _Araschnia Levana_, has two distinct varieties, -_Levana_ being the winter, and _prorsa_ the summer form; and between -these an intermediate form, _porima_, can be bred from the summer form -by keeping the pupæ cold. Dr. Weismann, who has largely experimented on -this insect, has given accurate illustrations of the varieties. Plate V. -is taken from specimens in our possession. In the males of both -_Levana_, Fig. 4, and _prorsa_, Fig. 1, the hind-wing has a distinct row -of spots, and a less distinct one inside it, and in the females of both -these are represented by dark stripes. In _porima_ we get every -intermediate form of spots and stripes, both in the male and female, and -as these were hatched from the same batch of eggs, or, are brothers and -sisters, it is quite impossible to doubt that here, at least, we have an -actual proof of the change of spots into stripes. - - [Illustration: Fig. 1. Part of secondary feather of Argus Pheasant. - _a. a._ Elongated spots, incipient ocelli. - _b._ Interspaces. - _c. c._ Axial line. - _d. d._ Double spots, incipient ocelli. - _e._ Minute dottings. - _f. f._ Shaft. - _k. k._ Line of feathering.] - - [Illustration: Fig. 2. Part of secondary wing feather of Argus - Pheasant. - _a._ Oval. Axis at right angles. - _b._ Round. - _c. c._ Shaft. - _d._ Imperfect ocellus. - _e._ Expansion of stripe. - _f._ Interspace. - _g._ Stalk. - _h._ Edge of feather. - _k._ Line of feathering.] - - [Illustration: Plate V. - SEASONAL VARIETIES.] - -The change of spots more or less irregular into eye-spots, or ocelli, is -equally clear; and Darwin's drawing of the wings of _Cyllo leda_[16] -illustrates the point well. "In some specimens," he remarks, "large -spaces on the upper surfaces of the wings are coloured black, and -include irregular white marks; and from this state a complete gradation -can be traced into a tolerably perfect ocellus, _and this results from -the contraction of the irregular blotches of colour_. In another series -of specimens a gradation can be followed from excessively minute white -dots, surrounded by a scarcely visible black line, into perfectly -symmetrical and larger ocelli." In the words we have put in italics -Darwin seems to admit these ocelli to be formed from blotches; and we -think those of the Argus pheasant can be equally shown to arise from -spots. - -Darwin's beautiful drawings show, almost as well as if made for the -purpose, that the bars are developed from spots.[17] In Fig. 1 is shown -part of a secondary wing feather, in which the lines _k. k._ mark the -direction of the axis, along which the spots are arranged, perfectly on -the right, less so on the left. The lengthening out of the spots towards -the shaft is well seen on the right, and the coalescence into lines on -the left. In Fig. 2 we have part of another feather from the same bird, -showing on the left elongated spots, with a dark shading round them, and -on the right double spots, like twin stars, with one atmosphere around -them. Increase the elongation of these latter, and you have the former, -and both are nascent ocelli. We here, then, have a regular gradation -between spots, bands, and ocelli, just as we can see in insects. - -In some larvæ, those of the _Sphingidæ_ especially, ocelli occur, and -these may be actually watched as they grow from dots to perfect -eye-spots, with the maturity of the larva. - -Even in some mammals the change from spots to stripes can be seen. -Thus, the young tiger is spotted, and so is the young lion; but, whereas -in the former case the spots change into the well-known stripes (which -are really loops), in the latter they die away. The horse, as Darwin -long ago showed, was probably descended from a striped animal, as shown -by the bars on a foal's leg. But before this the animal must have been -spotted; and the dappled horses are an example of this; and, moreover, -almost every horse shows a tendency to spottiness, especially on the -haunches. In the museum at Leiden a fine series of the Java pig (_Sus -vittatus_) is preserved. Very young animals are banded, but have spots -over the shoulders and thighs; these run into stripes as the animal -grows older; then the stripes expand, and, at last meeting, the mature -animal is a uniform dark brown. Enough has now, I trust, been said upon -this point to show that from spots have been developed the other -markings with which we are familiar in the animal kingdom. - -The vegetable kingdom illustrates this fact almost as well. Thus, the -beautiful leaves of the Crotons are at first green, with few or no -coloured spots; the spots then grow more in number, coalesce, form -irregular bands, further develop, and finally cover the whole, or almost -the whole, of the leaf with a glow of rich colour. Some of the pretty -spring-flowering orchid callitriche have sulphur-yellow petals, with -dark rich sepia spots; these often develop to such an extent as to -overspread nearly all the original yellow. Many other examples might be -given. - -Hitherto we have started with a spot, and traced its development. But a -spot is itself a developed thing, inasmuch as it is an aggregation of -similarly coloured cells. How they come about may, perhaps, be partly -seen by the following considerations. Definite colour-pattern has a -definite function--that of being seen. We may, therefore, infer that the -more definite colour is of newer origin than the less definite. Hence, -when we find the two sexes differently coloured, we may generally assume -that the more homely tinted form is the more ancient. For example, some -butterflies, like the gorgeous Purple Emperor (_Apatura iris_), have -very sombre mates; and it seems fair to assume that the emperor's robes -have been donned since his consort's dress was originally fashioned. - -That the object of brilliant colour is display is shown partly by the -fact that in those parts of the wings of butterflies which overlap the -brilliant colour is missing, and partly by the generally brighter hues -of day-flying butterflies and moths than of the night-flying species. -Now, the sombre hues of nocturnal moths are not so much protective (like -the sober tints of female butterflies and birds), because night and -darkness is their great defender, as the necessary result of the -darkness: bright colours are not produced, because they could not be -seen and appreciated. In these cases it is very noticeable how -frequently the colour is irregularly dotted about--irrorated or peppered -over the wings, as it were. This irregular distribution of the pigment -cells, if it were quite free from any arrangement, might be looked upon -as primitive colouring, undifferentiated either into distinct colour or -distinct pattern. If we suppose a few of the pigment cells here and -there to become coloured, we should have irregular brilliant dottings, -just as we actually see in many butterflies, along the costa. The -grouping together of these colour dots would give rise to a spot, from -which point all is clear. - -That some such grouping or gathering together, allied to segregation, -does take place, a study of spots, and especially of eye-spots, renders -probable. What the nature of the process is we do not know, nor is it -easy to imagine. But let us suppose a surface uniformly tinted brown. -Then, if we gather some of the colouring matter into a dark spot we -shall naturally leave a lighter area around it, just as we see in all -our Browns and Ringlets. In this way we can see how a ring-spot can be -formed. To make it a true eye-spot, with a light centre, we must also -suppose a pushing away of the colour from that centre. A study of ocelli -naturally suggests such a process, which is analogous to the banding of -agates, and all concentric nodules. Darwin, struck with this, seems to -adopt it as a fact, for he says, "Appearances strongly favour the belief -that, on the one hand, a dark spot is often formed by the colouring -matter being drawn towards a central point from a surrounding zone, -which is thus rendered lighter. And, on the other hand, a white spot is -often formed by the colour being driven away from a central point, so -that it accumulates in a surrounding darker zone."[18] The analogy -between ocelli and concretions may be a real one. At any rate beautiful -ocelli of all sizes can be seen forming in many iron-stained -sand-stones. The growth of ocelli may thus be a mechanical process -adapted by the creature for decorative purposes, but the artistic -colouring of many eye-spots implies greater effort. - -There is, however, one set of colour lines in birds and insects that do -not seem to arise from spots in the ordinary way. These are the coloured -feather-shafts of birds, and the coloured nerves or veins in a -butterfly's wing, In these the colour has a tendency to flow all along -the structure in lines. - -_Conclusion._ The results arrived at in this chapter may be thus -summarised:-- - -Spots, ocelli, stripes, loops, and patches may be, and nearly always -are, developed from more or less irregular spots. - -This is shown both by the study of normal colouring, or by abnormal -colouring, or decolouring in disease. - -Even the celebrated case of the Argus Pheasant shows that the bands from -which the ocelli are developed arose from spots. - - - [Illustration] - - - [11] Descent of Man, vol. ii., p. 132. - [12] Quart. Journ. Sci., July 1868, p. 325. - [13] Studies in the Theory of Descent. - [14] See photographs in Hutchinson's Illustrations of Clinical - Surgery. - [15] See Plate IV. - [16] Desc. Man, vol. ii, p. 133, fig. 52. - [17] Compare his figs. 56 to 58 op. cit. - [18] Desc. Man, vol. ii., p. 134. - - - - - CHAPTER VII. - - COLOURATION IN THE INVERTEBRATA. - - -If the principle of the dependence of colour-pattern upon structure, -enunciated in the preceding pages be sound, we ought to find certain -great schemes of colouration corresponding to the great structural -subdivisions of the animal kingdom. This is just what we do find; and -before tracing the details, it will be as well to group the great -colour-schemes together, so that a general view of the question can be -obtained at a glance. - -The animal kingdom falls naturally into two divisions, but the dividing -line can be drawn in two ways. If we take the most simple -classification, we have:-- - - 1. _Protozoa_, animals with no special organs. - - 2. _Organozoa_, animals possessing organs. - -Practically this classification is not used, but we shall see that from -our point of view it is a useful one. In the most general scheme the -divisions are:-- - - 1. _Invertebrata_, animals without backbones. - - 2. _Vertebrata_, animals with backbones. - -The invertebrata are divided into sub-kingdoms, of which the protozoa -form one. These protozoa possess, as it were, only negative properties. -In their simplest form they are mere masses of protoplasm, even lacking -an investing membrane or coat, and never, even in the highest forms, -possessing distinct organs. It is this simplicity which at once -separates them entirely from all other animals. - -The other sub-kingdoms are:-- - - _Coelenterata_, of which the jelly-fishes are a type; animals - possessing an alimentary canal, fully communicating with the - general cavity of the body, but without distinct circulatory or - nervous systems. - - _Annuloida_, of which the star-fishes are a type; animals having - the alimentary canal shut off from the body-cavity, and possessing - a nervous system, and in some a true circulatory system. - - _Annulosa_, of which worms, lobsters, and insects are types; - animals composed of definite segments, arranged serially, always - possessing true circulatory and nervous systems. - - _Mollusca_, of which oysters and whelks are types; animals which - are soft-bodied, often bearing a shell, always possessing a - distinct nervous system and mostly with a distinct heart. - -In old systems of classification, the _Coelenterata_ and _Annuloida_ were -united into one sub-kingdom, the _Radiata_, in consequence of their -radiate or star-like structures. - -As colouration, according to the views here set forth, depends upon -structure, we may classify the Invertebrata thus:-- - - Protozoa Structureless. - Coelenterata } Radiata. Radiate structure. - Annuloida } - Annulosa Segmented " - Mollusca Marginate " - -The mollusca are said to be marginate in structure because, in those -possessing shells--the mollusca proper--the shell is formed by -successive additions to the margin or edge of the shell, by means of the -margin of the mantle, or shell-secreting organ. - -Now we shall proceed to show that the schemes of colouration follow out -these structure-plans, and thus give additional force to the truth of -the classification, as well as showing that, viewed on a broad scale, -the present theory is a true one. - -We can, in fact, throw the whole scheme into a table, as follows:-- - - - SYSTEMS OF COLOURATION. - - +--+-------------------------+------------------------+------------------+ - | | System of Colouring. | Structure. | Sub-kingdoms. | - +--+-------------------------+------------------------+------------------+ - | |_A. No Axial Decoration._|_A. No Axial Structure._|_A. Invertebrata._| - |1.| No definite system. | No definite organs. | Protozoa. | - |2.| Radiate system. | Radiate structure. | Coelenterata, | - | | | | Annuloida.| - |3.| Segmental system. | Segmental structure. | Annulosa. | - |4.| Marginate system. | Marginate growth. | Mollusca. | - | | | | | - | | _B. Axial Decoration._ | _B. Axial Structure._ | _B. Vertebrata._ | - |5.| Axial system. | Axial structure. | Vertebrata. | - +--+-------------------------+------------------------+------------------+ - - -_Protozoa._ The protozoa are generally very minute, and always composed -of structureless protoplasm. Their peculiarities are rather negative -than positive, there being neither body segments, muscular, circulatory, -nor nervous systems. Even the denser exterior portion (_ectosarc_) -possessed by some of them seems to be rather a temporary coagulation of -the protoplasm than a real differentiation of that material. - -Here, then, we have to deal with the simplest forms of life, and if -colouration depends upon structure, these structureless transparent -creatures should lack all colour-pattern, and such is really the case. -Possessing no organs, they have no colouration, and are generally either -colourless or a faint uniform brown colour, and through their colourless -bodies the food particles show, often giving a fictitious appearance of -colouring. - -To this general statement there is a curious and most telling exception. -In a great many protozoa there exists a curious pulsating cell-like -body, called the contractile vesicle, which seems to be a rudimentary -organ, whose function is unknown. Here, then, if anywhere, traces of -colouring should be found, and here it is accordingly found, for, though -generally clear and colourless, it sometimes assumes a pale roseate hue. -This may be deemed the first attempt at decoration in the animal -kingdom, and it is directly applied to the only part which can be said -to possess structure. Beautiful examples are plentiful in Leidy's -magnificent volume on Freshwater Rhizopods. - -_Coelenterata._ These animals fall into two groups, the _Hydrozoa_, of -which the hydra and jelly-fishes are types, and the _Actinozoa_, of -which the sea-anemonies and corals are types. Most of the coelenterata -are transparent animals, but it is amongst them we first come across -opaque colouring. - -Of the lowest forms, the hydras, nothing need be said here, as they are -so much like the protozoa in their simplicity of structure. - -The _Corynida_, familiar to many of our sea-side visitors by their horny -brown tubes (_Tubularia_), attached to shells and stones, are next in -point of complexity. Within the tube is found a semi-fluid mass of -protoplasm, giving rise at the orifice to the polypite, which possesses -a double series of tentacles. These important organs are generally of a -vivid red colour, thus emphasizing their importance in the strongest -manner. Other members of the order are white, with pink stripes. - -In the larval stage many of the animals belonging to the above and -allied orders, are very like the true jelly-fishes. These free swimming -larvæ, or _gonophores_, possess four radiating canals, passing from the -digestive sac to the margins of the bell, and these are often the seat -of colour. In these creatures, too, we find the earliest trace of sense -organs, and consequently, the first highly differentiated organs, and -they appear as richly coloured spots on the margins of the bell. The -true oceanic Hydrozoa again afford us fine examples of structural -colouration. The beautiful translucent blue-purple _Velella_, which is -sometimes driven on to our shores, is a case in point; and its delicate -structure lines are all emphasized in deeper hues. The true jelly-fishes -(_Medusidæ_) with their crystal bells and radiating canals, frequently -show brilliant colour, and it is applied to the canals, and also to the -rudimentary eye-specks, which are frequently richly tinted, and in all -cases strongly marked. In the so-called "hidden-eyed" Medusæ we find the -same arrangement of colour, the same emphasized eye-specks, and the -reproductive organs generally appear as a vivid coloured cross, showing -through the translucent bell. - -Turning now to the _Actinozoa_, of which the sea anemonies and corals -are types, we are brought first into contact with general decorative, -more or less opaque colour, applied to the surface of the animal. In the -preceding cases the animals have been almost universally transparent or -translucent, and the colouration is often applied to the internal -organs, and shows through. In the sea-anemonies we find a nearer -approach to opacity, in the dense muscular body, though even this is -often translucent, and the tentacles generally so, often looking like -clouded chalcedony. The wealth of colour to be found in these animals -gives us a very important opportunity of studying decoration, where it -first appears in profusion. - -One of the first points that strikes even a casual observer is that -amongst the sea-anemonies the colouration is extremely variable, even in -the same species and in the same locality. This is in strong contrast to -what we generally find amongst the higher organisms, such as insects and -birds; for though considerable variation is found in them, it does not -run riot as in the anemonies. It would almost appear as if the actual -colour itself was of minor importance, and only the pattern essential; -the precise hue is not fixed, is not important, but the necessity of -colour of some sort properly arranged is the object to be attained. -Whether this idea has a germ of truth in it or not, it is hard to say, -but when we take the fact in connection with its occurrence just where -opacity begins, connecting this with the transparency of the lower -organisms, and the application of vivid colour to their internal organs, -one seems to associate the instability of the anemony's colouring with -the transference of colour from the interior to the exterior. Certain it -is, that vivid colour never exists in the interior of opaque animals; it -is always developed under the influence of light. The white bones, -nerves and cartilages, and the uniform red of mammalian muscles, are not -cases of true decorative colouring in our sense of the term, for all -bodies must have some colour. All bone is practically white, all -mammalian muscle red, but for these colours to be truly decorative, it -would be necessary for muscles of apparently the same character often to -be differently tinted, just as the apparently similar hairs on a mammal, -and scales on an insect, are variously painted. This we do not find, for -the shaft-bones and plate-bones, and even such odd bones as the hyoid -are all one colour; and no one would undertake to tell, by its hue, a -piece of striped from a piece of unstriped muscle. Decorative colouring -_must_ be external in an opaque animal; it _may_ be internal in a -transparent one. - -The connection thus shown between decoration and transparency seems to -suggest that hypodermal colour is the original, and epidermal the newer -scheme: that the latter was derived from the former. This agrees with -Haagen's shrewd hint that all mimetic colour was originally hypodermal. -Certain it is that the protective colour that is still under personal -control, as in the chameleon, &c., is always hypodermal. - -The common crass (_Bunodes crassicornis_) is so extremely variable, that -all one can say of it is, that it is coloured red and green. But this -colour is distributed in accordance with structure. The base, or -crawling surface, not being exposed to the light, is uncoloured. The -column, or stem, is irregularly spotted, and striped in accordance with -the somewhat undifferentiated character of its tissue, but the important -organs, the tentacles, are most definitely ornamented, the colour -varying, but the pattern being constant. This pattern is heart-shaped, -with the apex towards the point of the tentacle; that is to say, the -narrow part of the pattern points to the narrow part of the tentacle. - -In the common _Actinea mesembryanthemum_, which is often blood red, the -marginal bodies, probably sense-organs, are of the most exquisite -turquoise blue colour, and the ruby disc thus beaded is as perfect an -example of simple structural decoration as could be desired. A zone of -similar blue runs round the base of the body. - -Turning now to the corals, which are simply like colonies of single -anemonies with a stony skeleton, we have quite a different arrangement -of hues. No sight is more fascinating than that of a living-coral reef, -as seen through the clear waters of a lagoon. The tropical gardens -ashore cannot excel these sea-gardens in brilliancy or variety of -colour. Reds, yellows, purples, browns of every shade, almost bewilder -the eye with their profusion; and here again we find structural -decoration carried out to perfection. The growing points of white -branching corals (_Madrepores_) are frequently tipped with vivid purple, -and the tiny polyps themselves are glowing gem-stars. In the white -brain-corals, the polyps are vivid red, green, yellow, purple and so on; -but in almost every case vividly contrasting with the surrounding parts, -the colour changing as the function changes. - -The _Alcyonariæ_, which include the sea-fans, sea-pens, and the red -coral of commerce, practically bring us to the end of the _Coelenterata_, -and afford us fresh proof of the dependence of colour upon structure and -function. The well-known organ-pipe coral (_Tubipora musica_) is of a -deep crimson colour, and the polyps themselves are of the most vivid -emerald green, a contrast that cannot be excelled. Almost equally -beautiful is the commercial coral (_Corallium rubrum_) whose vivid red -has given a name to a certain tint. In this coral the polyps are of a -milk-white colour. - -It must be remembered that in these cases the colour seems actually to -be intentional, so as to form a real and not merely an accidental -contrast between the stony polypidom and the polyp, for the connecting -tissue (_coenosarc_) is itself as colourless as it is structureless. - -Gathering together the facts detailed in this chapter we find:-- - - 1. That the Protozoa are practically colourless and structureless. - - 2. That in those species which possess a rudimentary organ - (contractile vesicle) a slight decoration is applied to that - organ. - - 3. That in the Coelenterata the colouration is directly dependent - upon the structure. - - 4. That in transparent animals the colouration is applied directly - to the organ whether it be internal as in the canals or ovaries, or - external, as in the eye-specks. - - 5. That in opaque animals, as in the sea-anemonies, the colouring - is entirely external. - - 6. That it is very variable in hue, but not in pattern. - - 7. That the most highly differentiated parts (tentacles, - eye-specks), are the most strongly coloured. - - 8. That in the corals an emphatic difference occurs between the - colour of the polypidom (or "coral") and the polyp. - - - [Illustration] - - - - - CHAPTER VIII. - - DETAILS OF PROTOZOA. - - -The Protozoa are divided into three orders. - - I.--_Gregarinidæ._ - II.--_Rhizopoda._ - III.--_Infusoria._ - -I. The _Gregarinidæ_ consist of minute protozoa, parasitic in the -interior of insects, &c., and like other internal parasites are -colourless, as we should expect. - -II. The _Rhizopoda_ may, for our purpose, be divided into the naked -forms like _Amoeba_, and those which possess a skeleton, such as the -Radiolaria, the Foraminifera and the Spongia. - -Of these the naked forms are colourless, or uniformly tinted, excepting -the flush already described as emphasizing the contractile vesicle. - -The _Foraminifera_ are the earliest animals that possess a skeleton or -shell, and though generally very small, this shell is often complex, and -of extreme beauty, though their bodies retain the general simplicity of -the protozoa, indeed, they are said to possess no contractile vesicle. -Still the complexity of their shells places them on a higher level than -the naked rhizopoda. - -In these animals we find the first definite colour, not as a pattern, -but as simple tinting of the protoplasm. The general hue is -yellowish-brown (as in _Amoeba_), but deep red is not uncommon. The -deepest colour is found in the oldest central chambers, becoming fainter -towards the periphery, where it is often almost unrecognisable.[19] - -The _Radiolaria_ are minute organisms with still more complex skeletons, -and are considered by Haeckel[20] to be more highly organized than the -preceding order. They consist of a central portion containing masses of -minute cells, and an external portion containing yellow cells. Here we -have the first differentiation of parts in the external coating and -internal capsule, and side by side with this differentiation we find -colour more pronounced, and even taking regional tints in certain forms. - -We may notice the following genera as exhibiting fine colour:-- - - _Red._ Eucecryphalus, Arachnocorys, Eucrytidium, Dictyoceras. - - _Yellow._ Carpocanium, Dictyophimus, Amphilonche. - - _Purple._ Eucrytidium, Acanthostratus. - - _Blue._ Cyrtidosphæra, Coelodendrum. - - _Green._ Cladococeus, Amphilonche. - - _Brown._ Acanthometra, Amphilonche. - -Examples of these may be seen in the plates of Haeckel's fine work, and -as an illustration of regional decoration we cite _Acanthostratus -purpuraceus_, in which the central capsule is seen to run from red to -orange, and the external parts to be colourless, with red markings in -looped chains. - -_Spongocyclia_ also exhibits this regional distinction of colour very -clearly, the central capsule being red and the external portion yellow. - -The _Spongida_, or sponges, are, broadly speaking, assemblages or -colonies of amoeba-like individuals, united into a common society. -Individually the component animals are low, very low, in type, but their -union into colonies, and the necessity for a uniform or common -government has given rise to peculiarities that in a certain sense raise -them even above the complex radiolaria. Some, it is true, are naked, and -do not possess the skeleton that supports the colony, which skeleton -forms what we usually call the sponge; but even amongst these naked -sponges the necessity for communal purposes over and above the mere -wants of the individual, raises them a step higher in the animal series. -A multitude of individuals united by a common membrane, living in the -open sea, it must have happened that some in more immediate contact with -the food-producing waters, would have thriven at the expense of those in -the interior who could only obtain the nutriment that had passed -unheeded by the peripheral animals. But just as in higher communities we -have an inflowing system of water and an out-flowing system of effete -sewerage quite uncontrolled, and, alas, generally quite unheeded by the -individuals whose wants are so supplied; so in the sponges we have a -system of inflowing food-bearing water and an out-flowing sewage, or -exhausted-water system. This is brought about by a peculiar system of -cilia-lined cells which, as it were, by their motion suck the water in, -bringing with it the food, and an efferent system by which the exhausted -liquid escapes. These cilia-lined cells are the first true organs that -are to be found in the animal kingdom, and according to the views we -hold, they ought to be emphasized with colour, even though their -internal position renders the colouration less likely. This we find -actually to be the case, and these flagellated cells, as they are -called, are often the seat of vividest colour. - -The animal matter, or sarcode, or protoplasm of sponges falls into three -layers, just as we find the primitive embryo of the highest animals; and -just as the middle membrane of a mammalian ovum develops into bone, -muscle and nerve, so the middle membrane (mesosarc) of the sponges -develops the hard skeleton, and in this most important part we find the -colour cells prevail. Sollas, one of our best English authorities upon -sponges, writes, "The colours of sponges, which are very various, are -usually due to the presence of pigment granules, interbedded either in -the _endosarc of the flagellated cells_, or in the mesodermic cells, -usually of the skin only, but sometimes of the whole body."[21] - -We can, then, appeal most confidently to the protozoa as illustrating -the morphological character of colouration. - - - [Illustration] - - - [19] Leidy. Rhizopoda of N. America, p. 16. - [20] Haeckel. Die Radiolarien, Berlin, 1862. - [21] Sollas. Spongidæ. Cassell's Nat. Hist. Vol. vi., p. 318. - - - - - CHAPTER IX. - - DETAILS OF COELENTERATA. - - - I. HYDROZOA. - - _A. Hydrida._ - -The Hydras, as a rule, are not coloured in our sense of the term; that -is to say, they are of a general uniform brown colour. But in one -species, _H. viridis_, the endoderm contains granules of a green colour, -which is said to be identical with the green colouring matter of leaves -(_chlorophyll_). This does not occur in all the cells, though it is -present in most. The green matter occurs in the form of definite -spherical corpuscles, and these colour-cells define the inner layer of -the integument (the endoderm), and render it distinct.[22] That portion -of the endoderm which forms the boundary of the body-cavity has fewer -green corpuscles, but contains irregular brown granules, thus roughly -mapping out a structural region. - -We thus see that even in so simple a body as the Hydra the colouring -matter is distributed strictly according to morphological tracts. - -_B. Tubularida._ The Tubularian Hydroids are the subject of an -exhaustive and admirably illustrated monograph by Prof. J. Allman, from -which the following details are culled. These animals are with few -exceptions marine, and consist either of a single polypite or of a -number connected together by a common flesh, or coenosarc. Some are quite -naked, others have horny tubes, into which, however, the polypites -cannot retreat. The polypites consist essentially of a sac surrounded -with tentacles; and one of their most striking characters is their mode -of reproduction. Little buds (_gonophores_) grow from the coenosarc, and -gradually assume a form exactly like that of a jelly-fish. These drop -off, and swim freely about; and are so like jelly-fishes that they have -been classed among them as separate organisms. - -The Tubulariæ are all transparent; and in them we find structural -colouration finely shown, the colour, as is usual in transparent -animals, being applied directly to the different organs. - -Writing of the colour, Prof. Allman says: "That distinct secretions are -found among the Hydroida, and that even special structures are set aside -for their elaboration, there cannot now be any doubt. - -"One of the most marked of these secretions consists of a coloured -granular matter; which is contained at first in the interior of certain -spherical cells, and may afterwards become discharged into the somatic -fluid. These cells, as already mentioned, are developed in the -endoderm;[23] in which they are frequently so abundant as to form a -continuous layer upon the free surface of this membrane. It is in the -proper gastric cavity of the hydranth and medusa, in the spadix of the -sporosac, and in the bulbous dilatations which generally occur at the -bases of the marginal tentacles of the medusæ, that they are developed -in greatest abundance and perfection; but they are also found, more or -less abundantly, in the walls of probably the whole somatic cavity, if -we except that portion of the gastrovascular canals of the medusa which -is not included within the bulbous dilatations. - -"In the parts just mentioned as affording the most abundant supply of -these cells, they are chiefly borne on the prominent ridges into which -the endoderm is thrown in these situations; when they occur in the -intervals between the ridges they are smaller, and less numerous. - -"The granular matter contained in the interior of these cells varies in -its colour in different hydroids. In many it presents various shades of -brown; in others it is a reddish-brown, or light pink, or deeper -carmine, or vermilion, or orange, or, occasionally, a fine lemon-yellow, -as in the hydranth of _Coppinia arcta_, or even a bright emerald green, -as in the bulbous bases of the marginal tentacles of certain medusæ. No -definite structure can be detected in it; it is entirely composed of -irregular granules, irregular in form, and usually aggregated into -irregularly shaped masses in the interior of the cells. It is to this -matter that the colours of the _Hydroida_, varying, as they do, in -different species, are almost entirely due. - -"The coloured granular matter is undoubtedly a product of true -secretion; and the cells in which it is found must be regarded as true -secreting cells. These cells are themselves frequently to be seen as -secondary cells in the interior of parent cells, from which they escape -by rupture, and then, falling into the somatic fluid, are carried along -by its currents, until, ultimately, by their own rupture, they discharge -into it their contents. - -"We have no facts which enable us to form a decided opinion as to the -purpose served by this secretion. Its being always more or less deeply -coloured, and the fact of its being abundantly produced in the digestive -cavity, might suggest that it represented the biliary secretion of -higher animals. This may be its true nature, but as yet we can assert -nothing approaching to certainty on the subject; indeed, considering how -widely the cells destined for the secretion of coloured granules are -distributed over the walls of the somatic cavity, it would seem not -improbable that the import of the coloured matter may be different in -different situations; that while some of it may be a product destined -for some further use in the hydroid, more of it may be simply excretive, -taking no further part in the vital phenomena, and intended solely for -elimination from the system."[24] - -Here we have very definite statements by a highly trained observer of -the distribution of colour in the whole of these animals, and of the -conclusions he draws from them. - -Firstly as to the colour itself. We find it true colour--brown, pink, -carmine, vermilion, orange, lemon-yellow, and even emerald green; a set -of hues as vivid as any to be found in the animal kingdom. It is -difficult to conceive these granules to be merely excrementitious -matter; for in such simple creatures, feeding upon such similar bodies, -one would hardly expect the excretive matter to be so diversified in -tint. Moreover, excrementitious matter is not, as a rule, highly -coloured, but brown. Thus, we see in the Rhizopods the green vegetable -matter which has been taken in as food becomes brown as the process of -assimilation goes on; and, indeed, colour seems almost always to be -destroyed by the act of digestion. - -Still, it by no means follows that this colour, even if it is produced -for the sake of decoration, as we suggest, may not owe its direct origin -to the process of digestion. The digestive apparatus is the earliest -developed in the animal kingdom, and in these creatures is by far the -most important; the coelenterata being, in fact, little more than living -stomachs. If, then, colouration be structural, what is more likely than -that the digestive organs should be the seat of decoration in such -transparent creatures? - -Secondly, as to the distribution of the colour. We find it "frequently -forming a continuous layer upon the free surface of" the endoderm, in -the "spadix of the sporosac," and in the "bulbous terminations" of the -canals, that colour is best developed. In other words, the colour is -distributed structurally, and is most strongly marked where the function -is most important. - -Prof. Allman gives no hint that the colour may be purely decorative, and -is naturally perplexed at the display of hues in such vigour; but if -this be one of the results of the differentiation of parts, of the -specialization of function, then we can, at least, understand why we -find such brilliant colour in these creatures, and why it is so -distributed. - -As an illustration of the _Tubularia_ we have selected _Syncoryne -pulchella_, Fig. 2, Pl. VI., and its medusa, Fig. 1. The endoderm of the -spadix of the hydranths is of a rich orange colour, which becomes paler -as it descends towards the less highly organized stem. Medusæ are seen -in various stages of development, and one, mature and free, is shown. In -these the manubrium, and the bulbous terminations of the canals are also -seen to be coloured orange. - -In these medusæ we find the first appearance of sensory organs. They -consist of pigment-cells enclosed in the ectoderm, or outside covering; -and are singular as presenting the first true examples of opaque -colouring in the animal kingdom. They are associated with nerve cells -attached to a ring of filamentous nerve matter, surrounding the base of -the bell. In some important respects the pigment differs from that in -other parts of the animal. It is more definite in structure; and the -whole ocellus is "aggregation of very minute cells, each filled with a -homogeneous coloured matter."[25] These ocelli, and similar sense -organs, called _lithocysts_, are always situated over the bulbous -termination of the canals. The pigment is black (as in this case), -vermilion, or deep carmine. - - [Illustration: Plate VI. - SYNCORYNE PULCHELLA.] - -The dependence of colour upon structure is thus shown to hold good -throughout these animals in a most remarkable manner, and the acceptance -of the views here set forth gives us an insight into the reasons for -this colouration which, as we have seen, did not arise from the study of -the question from the ordinary point of view. - -_C. Sertularida._ These animals are very similar to the last, but they -are all compound, and the polypites can be entirely withdrawn within the -leathery investment or polypary. Their mode of reproduction is also -similar, and their colouration follows the same general plan. Being so -like the preceding order, it is unnecessary to describe them. - - - _B. Siphonophora._ - -The Siphonophora are all free-swimming, and are frequently called -Oceanic Hydrozoa. They are divided into three orders, viz.:-- - - _a. Calycophoridæ._ - _b. Physophoridæ._ - _c. Medusidæ._ - -_a. Calycophoridæ._ These animals have a thread-like coenosarc, or common -protoplasm, which is unbranched, cylindrical, and contractile. They are -mostly quite transparent, but where colour exists it is always placed -structurally. Thus, in _Diphyes_ the sacculi of the tentacles are -reddish, in _Sphæronectes_ they are deep red, and in _Abyla_ the edges -of the larger specimens are deep blue.[26] - -_b. Physophoridæ._ These creatures are distinguished by the presence of -a peculiar organ, the float, or _pneumatophore_, which is a sac -enclosing a smaller sac. The float is formed by a reflexion of both the -ectoderm and endoderm, and serves to buoy up the animal at the surface -of the sea. The best known species is the Physalia, or Portuguese -Man-o'-War. - -Prof. Huxley, in his monograph on the Oceanic Hydrozoa, gives many -details of the colouration; and, not having had much opportunity of -studying them, the following observations are taken from his work. It -will be seen that the Physophoridæ illustrate the structural -distribution of colour in a remarkable manner. - -_Stephanomia amphitridis_, the hydrophyllia, colourless, and so -transparent as to be almost imperceptible in water, coenosarc whitish, -enlarged portions of polypites, pink or scarlet, sacs of tentacles -scarlet. - -The enlarged portion of the polypites is marked with red striæ, "which -are simply elevations of the endoderm, containing thread-cells and -coloured granules." The small polypites do not possess these elevations, -and are colourless. - -_Agalma breve_, like a prismatic mass of crystal, with pink float and -polypites. - -_Athorybia rosacea_, float pink, with radiating dark-brown striæ, made -up of dots; polypites lightish red, shading to pink at their apices; -tentacles yellowish or colourless, with dark-brown sacculi; thread-cells -dark brown. - -_Rhizophysa filiformis_, pink, with deep red patch surrounding the -aperture of the pneumatocyst. - -_Physalia caravilla_, bright purplish-red, with dark extremities, and -blue lines in the folds of the crest; polypites violet, with whitish -points, larger tentacles red, with dark purple acetabula, smaller -tentacles blue, bundles of buds reddish. - -_P. pelagica_, in young individuals pale blue, in adult both ends green, -with highest part of crest purple, tentacles blue, with dark acetabula; -polypites dark blue, with yellow points. - -_P. utriculus._ Prof. Huxley describes a specimen doubtfully referred to -this species very fully, as follows:-- - - "The general colour of the hydrosoma is a pale, delicate green, - passing gradually into a dark, indigo blue, on the under surface. - - "The ridge of the crest is tipped with lake, and the pointed end is - stained deep bluish-green about the aperture of the pneumatocyst. - - "The bases of the tentacles are deep blue; the polypites deep blue - at their bases, and frequently bright yellow at their apices; the - velvetty masses of reproductive organs and buds on the under - surface are light green." - -He further remarks that the tentacles have reniform thickenings at -regular intervals, and "the substance of each thickening has a dark blue -colour, and imbedded within it are myriads of close-set, colourless, -spherical thread-cells." - -It would not be possible to find a more perfect example of regional -colouration. Not only is each organ differently coloured, but the -important parts of each organ, like the ridge of the crest, the bases of -the tentacles, and the thread-cell bearing ridges of the tentacles, are -also emphasized with deep colour. - -_Velella._ This beautiful creature, which sometimes finds its way to our -shores, is like a crystal raft fringed with tentacles, and having an -upright oblique crest, or sail. The margins of the disk and crest are -often of a beautiful blue colour, and the canals of the disk become deep -blue as they approach the crest. The polypites may be blue, purple, -green, or brown. - -_C. Medusidæ._ The structure and colouration of the true Medusæ are so -like that of the medusiform larvæ of the other Hydrozoa, that they need -not be particularly described. - -_D. Lucernarida._ Of this sub-class we need only cite the _Lucernaria_ -themselves; which are pretty bell-shaped animals, having the power of -attaching themselves to seaweeds, etc., and also of swimming freely -about. Round the margin are eight tufts of tentacles, opposite eight -lobes, the membrane between the lobes being festooned. In _L. auricula_, -a British species, the membrane is colourless and transparent, the lobes -bright red, or green, and the tentacles blue. - -As a group the Hydrozoa display regional colouration in a very perfect -manner. - - - II. ACTINOZOA. - -It is not necessary to trace the colouration through all the members of -this group, but we will trace the variation of colour through two -species of anemonies, which have been admirably studied by Dr. A. -Andres.[27] The first column shows the general hue, the second the tints -of that hue which are sufficiently marked to form varieties as cochineal -red, chocolate, bright red, rufous, liver-coloured, brown, olive, green -and glaucous. The third column gives the spotted varieties, from which -it will be seen that the chocolate, liver, and green coloured forms have -each coloured varieties. It will be seen that the range of colour is -very great, passing from pale pink, through yellowish-brown to -blue-green. - - -----------+-----------+-----------+---------------- - Prevailing | Uniform | Spotted | - colour. |varieties. |varieties. | Allied species. - -----------+-----------+-----------+---------------- - White. | ? | | A. candida. - " | coccinea. | | - " | chiocca. | tigrina. | - Red. | rubra. | | - " | rufosa. | | - Yellow. | hepatica. | fragacea. | - " | umbra. | | - " | olivacea. | | - " | viridis. | opora. | - " | glaucus. | | - Blue. | ? | | - -----------+-----------+-----------+---------------- - -Varieties of Actinea Cari. - -The following brief descriptions illustrate the distribution of the -colour:-- - -_Actinea Cari._ - -Uniform varieties (_Homochroma_). - - ----------------------+---------------+----------------+--------+----------- - | Column. | Tentacles. |Gonidia.| Zone. - ----------------------+---------------+----------------+--------+----------- - [alpha]. _Hepatica_ | red brown. | azure. | azure. | azure. - [beta]. _Rubra_ | crimson. | violet. | |{wanting, - [gamma]. _Chiocca_ | scarlet. | white. | |{or flesh - | | | |{coloured. - | | | | - [delta]. _Coccinea_ | cochineal. | yellowish. | | - [epsilon]. _Olivacca_ | olive-brown | azure. | azure. | - | green. | | | - [zeta]. _Viridis_ | green. | azure. | azure. | azure. - | | | | - Spotted varieties (_Heterochroma_). - | | | | - [eta]. _Tigrina_ |red, spotted | | | - | yellow. | | | - [theta]. _Fragacea_ |liver, spotted | | | - | clear green. | azure or white.| |indistinct. - [iota]. _Opora_ |green spotted, | | | - | and striped | | | - | yellow. | azure. | | - ----------------------+---------------+----------------+--------+----------- - -In this table the varieties above mentioned are further particularized. -The column is the stalk or body, the tentacles are the arms, the gonidia -the eye spots, and the zone the line round the base. It will be noticed -that these regions are often finely contrasted in colour. - -_Bunodes gemmaceus_ is another variable form, and the following -varieties are recognised. - -_Heterochroma._ - - [alpha]. Ocracea, } peristome ochre yellow, zone black, tentacles grey, - (type) } with blue and white spots. - - - [beta]. _Pallida_, peristome whitish grey unbanded, tentacles with - white spots. - - [gamma]. _Viridescens_, peristome greenish white unbanded, tentacles with - white spots and rosy shades. - - [delta]. _Aurata_, column at base golden, peristome intenser yellow with - crimson flush, tentacles grey with ochreous and white spots. - - [epsilon]. _Carnea_, column at base flesh coloured, peristome rosy, - tentacles rosy, with white spots. - -_Homochroma._ - - [zeta]. _Rosea_, like [epsilon], but with rosy tubercles. - - [eta] . _Nigricans_, peristome blackish, with blue and green - reflexions (riflessi). - -A few other examples may be given, all of which can be studied in Dr. -André's magnificently coloured plates. - -_Aiptasia mutabilis_ is yellow brown, the tentacles spotted in -longitudinal rows, the spots growing smaller towards the tip, thus -affording a perfect example of the adaptation of colour to structure. - -_Anemonia sulcata_ has normally long light yellow pendulous tentacles -tipped with rose, but a variety has the column still yellow but the -tentacles pale green, tipped with rose. - -_Bunodes rigidus_ has the column green, with rows of crimson tubercles, -the tentacles are flesh-coloured, except the outer row which are pearly; -the peristome is green, with brown lips. - - - [Illustration] - - - [22] Allman's Hydroids. Ray. Soc., p. 123. - [23] Compare with Hydra above. - [24] Allman. Monograph of Tubularian Hydroida. Ray. Soc., p. 135. - [25] Allman, _op. cit._, p. 139. - [26] Huxley. Oceanic Hydrozoa, pp. 32, 46, 50. - [27] Fauna und Flora des Golfes von Neapel. Die Actinien. 1884. - - - - - CHAPTER X. - - THE COLOURATION OF INSECTS. - - -In the decoration of insects and birds, nature has exerted all her -power; and amongst the wealth of beauty here displayed we ought to find -crucial tests of the views herein advocated. It will be necessary, -therefore, to enter somewhat into detail, and we shall take butterflies -as our chief illustration, because in them we find the richest display -of colouring. The decoration of caterpillars will also be treated at -some length, partly because of their beauty, and partly because amongst -them sexual selection cannot possibly have had any influence. - -Butterflies are so delicate in structure, so fragile in constitution, so -directly affected by changes of environment, that upon their wings we -have a record of the changes they have experienced, which gives to them -a value of the highest character in the study of biology. In them we can -study every variation that geographical distribution can effect; for -some species, like the Swallow-tail (_Papilio machaon_) and the Painted -Lady (_Cynthia cardui_), are almost universal, and others, like our now -extinct Large Copper (_Lycæna dispar_), are excessively local, being -confined to a very few square miles. From the arctic regions to the -tropics, from the mountain tops to the plains, on the arid deserts and -amidst luxuriant vegetation, butterflies are everywhere to be found. - -Before entering into details, it will be as well to sketch some of the -broad features of butterfly decoration. In the first place they are all -day-fliers, and light having so strong an influence upon colour, there -is a marked difference in beauty between them and the night-flying -moths. A collection of butterflies viewed side by side with a collection -of moths brings out this fact more strongly than words can describe, -especially when the apparent exceptions are considered; for many moths -are as brightly coloured as butterflies. These will be found to belong -either to day-flying species, like the various Burnets (_Zygæna_), Tiger -Moths (_Arctia_), or evening flyers like the Hawk Moths (_Sphyngidæ_.) -The true night-flying, darkness-loving moths cannot in any way compare -with the insects that delight in sunshine. We see the same thing in -birds, for very few nocturnal species, so far as we are aware, are -brilliantly decorated. - -Another salient feature is the difference that generally exists between -the upper and lower surfaces of the wings. As a rule, the upper surface -is the seat of the brightest colour. Most butterflies, perhaps all, -close their wings when at rest, and the upper wing is generally dropped -behind the under wing, so that only the tip is visible. The under -surface is very frequently so mottled and coloured as to resemble the -insect's natural surroundings, and so afford protection. It does not -follow that this protective colouring need be dull, and only when we -know the habit of the insect can we pronounce upon the value of such -colouring. The pretty Orange-tip has its under wings veined with green, -and is most conspicuous in a cabinet, but when at rest upon some -umbelliferous plant, with its orange tip hidden, these markings so -resemble the environment as to render the insect very inconspicuous. The -brilliant _Argynnis Lathonia_, with its underside adorned with plates of -metallic silver, is in the cabinet a most vivid and strongly-marked -species; but we have watched this insect alight among brown leaves, or -on brown stones, outside Florence, where it is very common, and find -that these very marks are a sure protection, for the insect at rest is -most difficult to see, even when it is marked down to its resting-place. - -But some butterflies have parts of the under surface as gaily decorated -as the upper; and this not for protection. This may be seen to some -extent in our own species, for instance in the orange-tip of the -Orange-tip, and the red bar in the upper wing of the Red Admiral (_V. -atalanta_). If we watch these insects, the conviction that these are -true ornaments is soon forced upon us. The insect alights, perhaps -alarmed, closes its wings, and becomes practically invisible. With -returning confidence it will gradually open its wings and slowly vibrate -them, then close them again, and lift the upper wing to disclose the -colour. This it will do many times running, and the effect of the sudden -appearance and disappearance of the bright hues is as beautiful as it -is convincing. None can doubt the love of display exhibited in such -actions. - -The delicacy of their organization renders butterflies peculiarly -susceptible to any change, and hence they exhibit strong tendencies to -variation, which make them most valuable studies. Not only do the -individuals vary, but the sexes are often differently coloured. Where -two broods occur in a season they are sometimes quite differently -decorated, and finally a species inhabiting widely different localities -may have local peculiarities. - -We can thus study varieties of decoration in many ways, and we shall -treat of them as follows:-- - - 1. _Simple Variation_, in which the different individuals of a - species vary in the same locality. - - 2. _Local Variation_, in which the species has marked peculiarities - in different localities. - - 3. _Sexual Dimorphism_, in which the sexes vary. - - 4. _Seasonal Dimorphism_, in which the successive broods differ. - - [Illustration: Fig. 3. Diagram of Butterfly's Wing. - A. Upper Wing. - B. Lower Wing. - _a._ Costal Margin. - _b._ Hind Margin. - _c._ Inner " - _d._ Anal Angle. - _e._ Costa. - _f._ Costal nervure. - _g._ Sub-costal do. - _g_^{1-4}. Branches of do. - _h._ Median nervure. - _i._ Sub-median do. - _j._ Discoidal Cell. - _k._ Discoidal Veins.] - -In order fully to understand the bearing of the following remarks it is -necessary to know something of the anatomy and nomenclature of -butterflies. Fig. 3 is an ideal butterfly. The wing margins are -described as the _Costal_, which is the upper strong edge of the wing, -the _Hind_ margin, forming the outside, and the _Inner_ margin, forming -the base. The nervures consist of four principal veins; the _Costal_, a -simple nervure under the costa, the _Sub-costal_, which runs parallel to -the costal and about halfway to the tip emits branches, generally four -in number; the _Median_ occupying the centre of the wing and sending off -branches, usually three in number, and the _Sub-median_ below which is -always simple. There are thus two simple nervures, one near the costal -the other near the inner margin, and between them are two others which -emit branches. Between these two latter is a wide plain space known as -the _discoidal cell_. Small veins called the _discoidal_ pass from the -hind margin towards the cell, and little transverse nervures, known as -sub-discoidal, often close the cell. By these nervures the wing is -mapped out into a series of spaces of which one, the discoidal cell, is -the most important. - -The nervures have two functions, they support and strengthen the wing, -and being hollow serve to convey nutritive fluid and afterwards air to -the wing. - -The wings are moved by powerful muscles attached to the base of the -wings close to the body and to the inside of the thorax, all the muscles -being necessarily internal. "There are two sets which depress the wings; -firstly a double dorsal muscle, running longitudinally upwards in the -meso-thorax;[28] and, secondly, the dorso-ventral muscles of the meso- -and meta-thorax,[29] which are attached to the articulations of the -wings above, and to the inside of the thorax beneath. Between these lie -the muscles which raise the wings and which run from the inner side of -the back of the thorax to the legs."[30] When we consider the immense -extent of wing as compared with the rest of the body, the small area of -attachment, and the great leverage that has to be worked in moving the -wings, it is clear that the area of articulation of the wing to the body -is one in which the most violent movement takes place. It is here that -the waste and repair of tissue must go on with greatest vigour, and we -should, on our theory, expect it to be the seat of strong emphasis. -Accordingly we commonly find it adorned with hairs, and in a vast number -of cases the general hue is darker than that of the rest of the wing, -and so far as we have been able to observe, never lighter than the body -of the wing. Even in the so-called whites (Pieris) this part of the wing -is dusky, and instances are numerous on Plate IV. - -The scales, which give the colour to the wings, deserve more than a -passing notice. They are inserted by means of little stalks into -corresponding pits in the wing-membrane, and overlap like tiles on a -roof; occasionally the attachment is a ball and socket (_Morphinæ_), in -which case it is possible the insect has the power of erecting and -moving its scales. The shapes are very numerous, but as a rule they are -short. To this there is a remarkable exception on the wings of the males -of certain butterflies, consisting of elongated tufted prominences which -appear to be connected with sense-organs. They are probably -scent-glands, and thus we find, even in such minute parts as scales, a -difference of function emphasized by difference of ornamentation, here -showing itself in variety of forms; but, as we have said, ornamentation -in form is often closely allied to ornamentation in colours. In some -butterflies, indeed, these scales are aggregated into spots, as in -_Danais_, and have a different hue from the surrounding area. - -The scales are not simple structures, but consist of two or more plates, -which are finely striated. The colouring matter consists of granules, -placed in rows between the striæ, and may exist upon the upper surface -of the upper membrane (epidermal), or the upper surface of the under or -middle plate (hypodermal), or the colour may be simple diffraction -colour, arising from the interference of the lightwaves by fine striæ. - -Dr. Haagen, in the admirable paper before mentioned, has examined this -question thoroughly, and gives the results set forth in the following -table:-- - - _Epidermal Colours._ - Metallic blues and greens } - Bronze } - Gold } - Silver } Persistent after death. - Black } - Brown } - Red (rarely) } - - _Hypodermal Colours._ - Blue } - Green } - Yellow } - Milk-white } Fading after death. - Orange and } - shades between } - Red } - -The hypodermal colours are usually lighter than the epidermal, and are -sometimes changed by a voluntary act. Hypodermal and epidermal colours -are, of course, not peculiar to insects; and, as regards the former, it -is owing to their presence that the changing hues of fishes, like the -sole and plaice, and of the chameleon are due. - -The great order Lepidoptera, including butterflies and moths, seems to -the non-scientific mind to be composed of members which are pretty much -alike, the differences being of slight importance; but this is not in -reality the case, for the lepidoptera might, with some accuracy, be -compared to the mammalia, with its two divisions of the placental and -non-placental animals. Comparing the butterflies (Rhopalocera) to the -placental mammals, we may look upon the different families as similar to -the orders of the mammalia. Were we as accustomed to notice the -differences of butterflies as we are to remark the various forms of -familiar animals, we should no longer consider them as slight, but -accord to them their true value. When in the mammalia we find animals -whose toes differ in number, like the three-toed rhinoceros and the -four-toed tapir, we admit the distinction to be great, even apart from -other outward forms. So, too, the seal and lion, though both belonging -to the carnivora, are readily recognized as distinct, but the seals may -easily be confounded by the casual observer with the manatees, which -belong to quite a different order. - -Thus it is with the Lepidoptera, for from six-legged insects, whose pupæ -lie buried beneath the soil, like most moths, we pass to the highest -butterflies, whose fore-legs are atrophied, and whose pupæ hang -suspended in the open air; and this by easy intermediate stages. Surely, -if six-legged mammals were the rule, we should look upon four-legged -ones as very distinct; and this is the case with the butterflies. It is -necessary to make this clear at starting, in order that we may -appreciate to its full value the changes that have taken place in the -insects under study. - -Butterflies (_Rhopalocera_) are grouped into four sub-families, as -under:-- - - 1. _Nymphalidæ_, having the fore-legs rudimentary, and the pupæ - suspended from the base of the abdomen. - - 2. _Erycinidæ_, in which the males only have rudimentary fore-legs. - - 3. _Lycænidæ_, in which the fore-legs of the males are smaller than - those of the females, and terminate in a simple hook. - - 4. _Papilionidæ_, which have six perfect pairs of legs, and in - which the pupæ assume an upright posture, with a cincture round the - middle. - -It may, at first sight, appear curious that the imperfect-legged -_Nymphalidæ_ should be placed at the head of the list, but this is based -upon sound reasoning. The larva consists of thirteen segments, and, in -passing to the mature stage, the second segment alone diminishes in -size, and it is to this segment that the first pair of legs is attached. -Looking now to the aerial habits of butterflies, we can understand how, -in the process of evolution towards perfect aerial structure, the legs, -used only for walking, would first become modified; and, naturally, -those attached to the segment which decreases with development would be -the first affected. When this is found to be combined with an almost -aerial position of the pupæ, we see at once how such insects approach -nearest to an ideal flying insect. It is a general law that suppression -of parts takes place as organisms become specialized. Thus, in the -mammalia, the greatest number of toes and teeth are found in the lowest -forms and in the oldest, simplest fossil species. - -A butterfly is, indeed, little more than a beautiful flying machine; for -the expanse of wing, compared with the size of the body, is enormous. - - - [Illustration] - - - [28] The middle division of the thorax. - [29] Hinder division of thorax. - [30] Dallas in Cassell's Nat. Hist., vol. vi., p. 27. - - - - - CHAPTER XI. - - THE COLOURATION OF INSECTS. - - (_Continued._) - - -_General Scheme of Colouring._ So various are the patterns displayed -upon the wings of butterflies, that amidst the lines, stripes, bars, -dots, spots, ocelli, scalloppings, etc., it seems at first hopeless to -detect any general underlying principle of decoration; and this is the -opinion that has been, and is still, held by many who have made these -insects a special study. Nevertheless, we will try to show that beneath -this almost confused complexity lie certain broad principles, or laws, -and that these are expressed by the statement that decoration is -primarily dependent upon structure, dependent upon the laws of emphasis -and repetition, and modified by the necessity for protection or -distinction. - -To render this subject as plain as possible, British species will be -selected, as far as possible, and foreign ones only used when native -forms do not suffice. - -The body of by far the greater number of species is either darker or of -the same tint as the mass of the wings; and only in rare cases lighter. -When the body has different tints, it is generally found that the thorax -and abdomen differ in colour, and in many cases the base of the thorax -is emphasized by a dark or light band. - -On the wings the functional importance of the parts attached to the body -is generally darker, perhaps never lighter, than the ground of the wing, -and is frequently further emphasized by silky hairs. This has already -been sufficiently pointed out. - -The wing area may be divided into the strong costal margin, the hind -margin, the nervules, and the spaces; and, however complex the pattern -may be, it is always based upon these structure lines. - -In the majority of insects the costal margin is marked with strong -colour. This may be noticed in _Papilio Machaon_, _P. merope_, _Vanessa -antiopa_, and the whites in Plate IV. The extreme tip of the fore-wings -is nearly always marked with colour, though this may run into the border -pattern. This colour is dark or vividly bright, and we know no -butterfly, not even dark ones, that has a light tip to the wings. -Sometimes, it is true, the light bead-border spots run to the tip, but -these are not cases in point. The development of tips has been traced in -Chapter VI., and need not be repeated. - -The hind margin of both wings is very commonly emphasized by a border, -of which _V. Antiopa_, Pl. III. Fig. 3, is a very perfect example. - -The border pattern may consist of one or more rows of spots, lines, -bands, or scallops;[31] and there is frequently a fine fringe, which in -many cases is white, with black marks, and to which the term -bead-pattern may be applied. - -A definite relation subsists in most cases between the shape of the hind -margin and the character of the border-pattern. The plain or simple -bordered wings have plain border patterns, and the scalloped wings have -scalloped borders; or rather scalloped borders are almost exclusively -confined to scalloped wings. In our English butterflies, for instance, -out of the 62 species:-- - - 33 have plain margins to the wings. In all the border is plain, or - wanting. - - 20 have the fore-wings plain, and the hind-wings scalloped, and in - all the hind-wings are scalloped and the fore-wings plain, or with - slightly scalloped border-patterns. - - 9 have scalloped margins and scalloped border-patterns. - -Another relation between structure and pattern is found in those insects -which have tailed hind-wings, for the tail is very frequently emphasized -by a spot, often of a different colour from the rest of the wing as in -the Swallow-Tails, Plates IV. and V. - -Yet another point may be noticed. In each wing there is a space, the -discoidal cell, _j_ Fig. 3, at the apex of which several nervures join, -forming knots. These are points at which obstacles exist to the flow of -the contents, and they are almost always marked by a distinct pattern. -We thus have a discoidal spot in very many butterflies, in nearly all -moths; and in the other orders of winged insects the decoration is even -more pronounced, as any one may see who looks at our dragon-flies, -wasps, bees, or even beetles. - -In some insects the decoration of the body is very marked, as in our -small dragon-flies, the Agrions. In one species, for example, _A. -Puella_, the male is pale blue banded with black, and the female bronze -black, with a blue band on the segment, bearing the sexual organ; the -ovipositors are also separately decorated. The male generative organs -are peculiar, in that the fertilizing fluid is conveyed from one segment -to a reservoir at the other end of the abdomen. Both the segments -bearing these organs are marked by special decoration. The peculiar -arrangement of the sexual organs in dragon-flies is very variable, and -certain segments are modified or suppressed in some forms, as was shown -by J. W. Fuller.[32] In every case the decoration follows the -modification. In the thorax of dragon-flies, too, the principal muscular -bands are marked out in black lines. This distinct representation of the -internal structure is beautifully shown in _Æschna_ and _Gomphina_, and -in the thorax of _Cicada_, as shown by Dr. Haagen in the paper quoted in -the last chapter. - -We may, then, safely pronounce that the decoration of insects is -eminently structural. - -_Simple Variation._ Cases of simple variation have been already cited in -our description of spots and stripes, and it only remains to show that -in this, as in all other cases, the variation is due to a modification -of original structural decoration. - -To take familiar examples. Newman, in his British Butterflies, figures -the varieties of the very common Small Tortoiseshell (_Vanessa urticæ_). -In the normal form there is a conspicuous white spot on the disc of the -fore-wings, which is absent in the first variety, owing to the spreading -of the red-brown ground colour. This variety is permanent on the -Mediterranean shores. In variety two, the second black band, running -from the costa across the cell, is continued across the wing. The third -variety, Mr. Newman remarks, is "altogether abnormal, the form and -colouring being entirely altered." Still, when we examine the insect -closely, we find it is only a modification of the original form. The -first striking difference is in the margin of the wings, which in the -normal form is scalloped with scallop-markings, whereas, in the variety -the margins are much simpler, and the border pattern closely corresponds -with it, having lost its scalloping. In the fore-wing some of the black -bands and spots are suppressed or extended, and the extensions end -rigidly at nervules. The dark colouring of the hind-wings has spread -over the whole wing. We thus see that the decoration, even in varieties -called abnormal, still holds to structural lines, and is a development -of pre-existing patterns. - -No one can have examined large series of any species without being -impressed with the modification of patterns in almost every possible -way. For instance, we have reared quantities of _Papilio Machaon_, and -find great differences, not only in the pattern, but in the colour -itself. A number of pupæ from Wicken Fen, Cambridgeshire, were placed in -cages, into which only coloured light could fall, and though these -experiments are not sufficiently extended to allow us to form any sound -conclusions as to the effect of the coloured light, we got more -varieties than could be expected from a batch of pupæ from the same -locality. The tone of the yellow, the quantity of red, the proportion of -the yellow to the blue scales in the clouds, varied considerably, but -always along the known and established lines. - -The variations in the colour of Lepidoptera has been most admirably -treated by Mr. J. Jenner Weir in a paper, only too short, read before -the West Kent Natural History Society.[33] He divides variations into -two sections, Aberrations or Heteromorphism, and constant variations or -Orthopæcilism, and subdivides each into six classes, as under:-- - - _Heteromorphism._ - - Albinism ... ... white varieties. - - Melanism ... ... black do. - - Xanthism ... ... pallid do. - - Sports ... ... or occasional variations not included - in the above. - - Gynandrochomism ... females coloured as males. - - Hermaphroditism ... sexes united. - - _Orthopæcilism._ - - Polymorphism ... variable species. - - Topomorphism ... local varieties. - - Atavism ... ... reversion to older forms. - - Dimorphism ... ... two constant forms. - - Trimorphism ... ... three do. do. - - Horeomorphism ... seasonal variation. - - - -In some cases, he remarks, variations are met with which may with equal -propriety be classed in either section. - -Albinism he finds to be very rare in British species, the only locality -known to him being the Outer Hebrides. This reminds us of Wallace's -remark upon the tendency to albinism in islands. Xanthism, he finds to -be more plentiful, and quotes the common Small Heath (_Cænonympha -pamphilus_) as an illustration. In these varieties we have simply a -bleaching of the colouring matter of the wings, and therefore no -departure from structural lines. Melanism arises from the spreading of -large black spots or bars, or, as in _Biston betularia_, a white moth -peppered with black, dots by the confluence of small spots; for this -insect in the north is sometimes entirely black. It is singular that -insects have a tendency to become melanic in northern and alpine places, -and this is especially the case with white or light coloured species. -(_See_ Plate IV., Fig. 17) It has recently been suggested that this -darkening of these delicate membranous beings in cold regions is for the -purpose of absorbing heat, and this seems very probable.[34] - -Of ordinary spots it is merely necessary to remark, that they are all -cases in our favour. Thus, in _Satyrus hyperanthus_ we have "the -ordinary round spots ... changed into lanceolate markings"; this takes -place also in _C. davus_. The other cases of aberration do not concern -us. - -When, however, we come to the cases in which a species has two or more -permanent forms, it is necessary to show that they are in all cases -founded on structure lines. The patterns, as shown in Plate V., Figs. -1-13, are always arranged structurally, and the fact that not only are -intermediate forms known, as in _Araschnia porima_, Plate V., Fig. 6, -but that the various forms are convertible into one another, would in -itself be sufficient to show that in these cases there is no departure -from the general law. In _Grapta interrogationis_, Plate V., Figs. 8-10, -we see in the central figure one large spot above the median nervure, in -the left-hand form this is surmounted by another spot above the lowest -sub-costal branch, and in the right-hand figure this latter spot is very -indistinct. We have here a perfect gradation, and the same may be said -of the colouration of the lower wings. Take again the three forms of -_Papilio Ajax_ in the same plate, Figs. 11-13, and we have again only -modifications of the same type. - -In local varieties, as in seasonal forms, we have again nothing more -than developments of a given type, as is well shown in Plates IV. & V., -Figs. 13-18 & 1-13. - -When, however, we come to mimetic forms, whether they mimic plants, as -in Plate I., or other species, as in Plates II. & III., a difficulty -does seem to arise. - -The leaf butterfly (_Kallima inachus_), Plate I., offers no trouble when -we view the upper surface only with its orange bands, but its under -surface, so marvellously like a dead leaf that even holes and -microscopic fungi are suggested, does seem very like a case in which -structure lines are ignored. Take, for instance, the mark which -corresponds to the mid-ribs, running from the tail to the apex of the -upper wing; it does not correspond to any structure line of the insect. -But if we take allied and even very different species and genera of -Indian and Malayan butterflies, we shall find every possible -intermediate form between this perfect mimicry and a total lack of such -characters. To cite the most recent authority, the various species of -the Genera Discophora, Amathusia, Zeuxidia, Thaumantis, Precis, &c., -figured so accurately in Distant's Rhopalocera Malayana, will give all -the steps. - -In the cases of true mimicry, as in Figs. 1-3, Plates II. & III., where -insects as different as sheep from cats copy one another, we find that -of course structure lines are followed, though the pattern is vastly -changed. The _Papilio merope_, Fig. 1, Plate II., which mimics _Danais -niavius_, Fig. 3, does so by suppressing the tail appendage, changing -the creamy yellow to white--a very easy change, constantly seen in our -own Pieridæ--and diffusing the black. A similar case is seen in Figs. -4-5, Plate III., where a normally white butterfly (_Panopoea hirta_) -mimics a normally dark one of quite a different section. Here again the -change is not beyond our power of explanation. Where a Papilio like -_merope_ mimics a brown species like _Danais niavius_, we have a still -greater change in colour, but not in structural pattern. - -If we ascribe to these insects the small dose of intelligence we believe -them to possess, we can readily see how the sense of need has developed -such forms. - -Local varieties present no difficulty under such explanation. The -paramount necessity for protection has given the Hebridran species the -grey colour of the rocks, and the desert species their sandy hue. - - [Illustration: Plate VII. - CATERPILLARS.] - -Finally, to take the case of caterpillars, Weismann has admirably worked -out the life history of many forms, and shows how the complex markings -have arisen by development. Broadly, a caterpillar consists of 13 -segments, the head being one. The head is often marked with darker -colour, and the last segment with its clasping feet is also very -frequently emphasized, as in Figs. 1 & 3, Plate VII. The spiracles are -generally marked by a series of spots, and often connected by a line. -Here the tendency to repetition shows itself strongly, for not only the -spiracles themselves, but the corresponding points in the segments -without spiracles are frequently spotted, and, moreover, these spots are -frequently repeated in rows above the spiracular line. Of this, -_Deilephila galii_ and _D. Euphorbiæ_, Figs. 1-5, Plate VII., are good -examples. - -The segmentation is also generally emphasized, as shown in all the -examples on the plate, but in its simplicity in Fig. 10. - -Running down the centre of the back a more or less distinct line is -often seen, as shown in the figures. This corresponds with the great -dorsal alimentary canal lying just below the skin, and Weismann has -shown that in young larvæ this line is transparent, and the green food -can be seen through the skin. We have here, perhaps, a relic of the -direct colouration noticed in the transparent coelenterata. - -Where larvæ possess horns either upon the head, as in _Apatura iris_ and -_Papilio machaon_, or on the tail, as in many of the sphyngidæ, like -Figs. 1-5, Plate VII., these appendages are always emphasized in colour. -As they are frequently oblique, we often find that this obliquity is -continued as a slanting spot, as in _D. galii_ and _euphorbiæ_, and -sometimes repeated as a series of oblique stripes, as in Fig. 4. - -It must be admitted that in insects we have strong evidence of -structural decoration. - - - [Illustration] - - - [31] In the true scallop pattern the convexity is turned towards the - body of the insect. - [32] J. W. Fuller on the Breathing Apparatus of Aquatic Larvæ. Proc. - Bristol Nat. Soc. - [33] Entomologist, vol. xvi., p. 169, 1883. - [34] Nature. R. Meldola on Melanism, 1885. - - - - - CHAPTER XII. - - ARACHNIDA. - - -The Arachnida include the scorpions and spiders, and as the former are -tolerably uniform in colour, our remarks will be confined to the latter. - -The thorax is covered with a horny plate, while the abdomen only -possesses a soft skin, and neither show any traces of segmentation. From -the thorax spring four pairs of legs, and a pair of palpi, or feelers. -Immediately beneath the skin of the abdomen lies the great dorsal -vessel, which serves as a heart. This vessel is divided into three -chambers, the general aspect of which is shown in Fig. 9, Plate VIII., -taken from Gegenbaur's Comparative Anatomy.[35] - -From this heart the blood passes by vessels to each of the limbs, the -palpi, etc., as offsets from the double-branched aorta. The shape of -this dorsal vessel is peculiar, and its importance in respect to -colouration will be immediately apparent. - -The primary scheme of colouration in the Arachnida seems to be the -distinguishing of the cephalothorax from the abdomen by a different -colour. Thus, of the 272 species of British spiders represented in -Blackwell's work,[36] no less than 203 have these parts differently -coloured, and only 69 are of the same hue, and even in these there is -often a difference of tint. So marked is this in certain cases that the -two parts form vivid contrasts. Of this cases are given in the following -list. - - Cephalothorax. Abdomen. - _Eresus cinnabarinus_, Black, Bright Red. - _Thomisus floricolens_, Green, Brown. - ---- _cinereus_, Brown, Blue. - ---- _trux_, Red, Brown. - _Sparassus smaragdulus_, Green, Red and yellow. - -As a rule the abdomen is darker than the cephalothorax, and many species -have the former red-brown and the latter black. - -The legs, usually, take the colour of the cephalothorax, and are, hence, -generally lighter than the abdomen, but to this there are exceptions. -Where the individual legs differ in colour, the two first pairs are the -darkest, and the dark hue corresponds in tint with the dark markings on -the cephalothorax. The joints of the legs are in many species emphasized -with dark colour, which is often repeated in bands along the limb. - -The most remarkable point is, however, the pattern on the abdomen, -which, though varied in all possible ways, always preserves a general -character, so that we might speak with propriety of a spider-back -pattern. This pattern is fairly well illustrated in the genus _Lycosa_, -but is seen to perfection, and in its simplest form in _Segestria -senoculata_, Plate VIII., Fig. 1, and in _Sparassus smaragdulus_, Plate -VIII., Fig. 2. - -This peculiar pattern is so like the dorsal-vessel that lies just -beneath, that it is difficult to avoid the conclusion that we have here -an actual case of the influence of internal organs on the integument, -and this we believe to be the case. No matter how curious the abdominal -markings may seem to be, they never so far depart from this fundamental -pattern as to appear independent of it. - -Thus, in the genus _Lycosa_, which is by no means the best for the -purpose, but is chosen as illustrating Gegenbaur's diagram, Pl. VIII., -we have the dorsal-vessel well marked in _L. piscatoria_, Plate VIII., -Fig. 3, from which may be developed the other forms. In _L. -andrenivora_, Plate VIII., Fig. 4, the male shows the vessel-mark -attenuated posteriorly; and in the female, Fig. 5, the hinder part has -become broken up into detached marks, still preserving the original -shape, while the upper part remains practically unchanged. In _L. -allodroma_ the disintegration of the mark has further advanced, for in -the male, Fig. 6, the upper portion has lost something of its shape, and -the lower part is a series of isolated segments. This process is carried -still further in the female, Fig. 8, where the upper portion is -simplified, and the lower almost gone. In _L. campestris_, Fig. 10, the -mark is reduced to a stripe, corresponding with the upper part of the -vessel-mark only: and, lastly, in the male _L. agretyca_, Fig. 7, this -upper part is represented by two spots, though even here traces of the -original form can be seen. - -A simplification of marking of another sort is seen in _L. rapax_, Fig. -13, where the chamber-markings are almost obliterated, and merely an -irregular stripe left. The stages by which this modification is arrived -at are too obvious to need illustration. - -In some species the lower portion of the vessel-mark is reduced to small -dots, as in _L. cambrica_, _fluviatilis_, _piratica_, and others; and -the stages are very clear. Starting with the isolated chamber-marks, as -in _L. allodroma_, Fig. 5, we get, firstly, a set of spots, as in _L. -picta_, which, in the female, Fig. 16, are still connected with the -chamber-marks, but in the male, Fig. 17, are isolated. This leads us, by -easy steps, to such forms as _L. latitans_, Fig. 14, which consists of a -double row of spots upon dark stripes. - -The intimate connection thus shown to subsist between the characteristic -decoration of the abdomen of spiders, and the shape of the important -dorsal organ beneath, seems to be strong evidence of effect that -internal structure may have upon external decoration.[37] - -The cephalothorax of spiders, being covered with a hardened membrane, -does not show such evidence clearly, for it appears to be a law that the -harder the covering tissue, the less does it reflect, as it were, the -internal organs. The hard plates of the armadillo are thus in strong -contrast to the softer skins of other animals. - -Nevertheless, there does appear, occasionally, to be some trace of this -kind of decoration in the cephalothorax of certain spiders, though it -would be hard to prove. The blood vessels of this part (see Fig. 9), -though large, are not nearly so prominent as the great dorsal vessel. -The chief artery enters the cephalothorax as a straight tube, forks, and -sends branches to the limbs, palpi, and eyes. In many species, notably -in the genus _Thomisus_, a furcate mark seems to shadow the forked -aorta. This is best shown in _T. luctuosus_, Plate VIII., Fig. 11. -Moreover, in this and other genera, lines frequently run to the outer -pair of eyes, which alone are supplied with large arteries, see Fig. 9. - -However this may be, it is certain that the entire decoration of spiders -follows structural lines, and that the great dorsal vessel has been -emphasized by the peculiar pattern of the abdomen. - - [Illustration: Plate VIII. - SPIDERS.] - - - [35] Elements of Comparative Anatomy, by C. Gegenbaur. Translated by - Jeffrey Bell and Ray Lankester, 1878, p. 285. - [36] Spiders of Great Britain and Ireland, J. Blackwell. Ray. Soc., - 1861. - [37] The decoration of many of the Hoverer flies and wasps is of a - similar character. - - - - - CHAPTER XIII. - - COLOURATION OF INVERTEBRATA - (_Continued_). - - -Of the Arthropoda, including the lobsters, crabs, shrimps, etc., little -can be said here, as we have not yet been able to study them with -anything like completeness. Still, we find the same laws to hold good. -The animals are segmented, and we find their system of colouration -segmental also. Thus, in the lobsters and crabs there is no dorsal line, -but the segments are separately and definitely decorated. The various -organs, such as the antennæ and eyes, are picked out in colour, as may -be beautifully seen in some prawns. - -When we come to the Mollusca, we meet with two distinct types, so far as -our subject is concerned; the naked and the shelled. In the naked -molluscs, like the slugs, we have decoration applied regionally, as is -shown to perfection in the _Nudibranchs_, whose feathery gills are often -the seat of some of the most vivid hues in nature. - -The shell-bearing mollusca are proverbial for their beauty, but it is -essential to bear in mind that the shell does not bear the same relation -to the mollusc that the "shell" of a lobster does to that animal. The -lobster's shell is part of its living body; it is a true exo-skeleton, -whereas the shell of a mollusc is a more extraneous structure--a house -built by the creature. We ought, on our view, to find no more relation -between the decoration of a shell and the structure of its occupant, -than we do in the decoration of a human dwelling-house to the tenant. - -The shell consists of carbonate of lime, under one or both of the forms -known to mineralogists as calcite and aragonite. This mineral matter is -secreted by an organ called the mantle, and the edge, or lip, of the -mantle is the part applied to this purpose. The edge of the mantle is -the builder's hand, which lays the calcareous stones of the edifice. -The shell is built up from the edge, and the action is not continuous -but seasonal, hence arise the markings known as lines of growth. In some -cases the mantle is expanded at times into wing-like processes, which -are turned back over the shell, and deposit additional layers, thus -thickening the shell. - -In all the forms of life hitherto considered the colouring matter is -deposited, or formed, in the substance of the organ, or epidermal -covering, but in the mollusca this is not the case. The colouring matter -is entirely upon the surface, and is, as it were, stencilled on to the -colourless shell. This is precisely analogous to the colouring of the -shells of birds' eggs. They, too, are calcareous envelopes, and the -colouring matter is applied to the outside, as anyone can see by rubbing -a coloured egg. In some eggs several layers of colouring matter are -superimposed. - -In no case does the external decoration of molluscan shells follow the -structure lines of the animal, but it does follow the shape of the -mantle. The secreting edge may be smooth, as in _Mactra_, regularly -puckered, as in most _Pectens_, puckered at certain points, as in -_Trigonia_, or thrown into long folds, as in _Spondylus_. In each of -these cases the shell naturally takes the form of the mantle. It is -smooth in _Mactra_, regularly ribbed in _Pecten_, tubercled in -_Trigonia_, and spined in _Spondylus_. Where the inside of the shell is -coloured as in some Pectens, regional decoration at once appears and the -paleal lines, and muscular impressions are bounded or mapped out with -colour. - -It is a significant fact that smooth bivalves are not so ornate as -rugose ones, and that the ridges, spines, and tubercles of the latter -are the seats of the most prominent colour. - -Similar remarks apply to univalve shells, which are wound on an -imaginary vertical axis. They may be smooth, as in _Conus_ and _Oliva_, -rugose, as in _Cerithium_, or spined, as in _Murex_. The structure of -these shells being more complex than that of bivalves, we find, as a -rule, they are more lavishly ornamented, and the prominent parts of the -shell, and especially the borders, are the seat of strongest colour. In -some cases, as in adult Cowries (_Cypræa_), the mantle is reflexed so as -to meet along the median line, where we see the darkest colour. - -The rule amongst spiral shells is to possess spiral and marginal -decoration, and this is what we should expect. The Nautilus repeats in -the red-brown markings of its shell, the shape of the septa which -divide the chambers, though, as is often the case, they are generally -more numerous than the septa. - -The naked Cephalopoda, or cuttle-fishes, often possess a distinct dorsal -stripe, and when our views were first brought before the Zoological -Society, this fact was cited as an objection. To us it seems one of the -strongest of favourable cases, for these animals possess a sort of -backbone--the well-known cuttle-bone--and hence they have a dorsal line. - -Some shells, as _Margarita catenata_, have a chain-pattern, and in this -case the action of the pigment cells takes place at regular and short -intervals. Others, as _Mactra stultorum_, the stencilling forms a series -of lines and spots, generally enlarging into rays. - -The whole subject of the decoration of shells deserves much more time -than we have been able to give to it as yet. - - - [Illustration] - - - - - CHAPTER XIV. - - COLOURATION OF VERTEBRATA. - - -The vertebrata, as their name implies, are distinguished by the -possession of an internal skeleton, of which the backbone is the most -essential part, and the general, but not universal, possession of limbs -or appendages. - -Consequently we find that the dorsal and ventral surfaces are almost -invariably coloured differently, and the dorsal is the darker in the -great majority of instances. Generally the spine is marked by a more or -less defined central line, and hence this system of colouration may be -termed axial, because it is in the direction of the axes, or applied -about the axes. - -_Fishes._ Where fishes have not been modified out of their original -form, as are the soles, plaice, and other flat fish, we find the dorsal -region darker than the ventral, and even here the under surfaces are the -lightest. Even in cases like the Char, Fig. 1, Plate IX., where vivid -colour is applied to the abdomen, the dorsum is the darker. The dorsum -is often marked by a more or less well-defined dark band, as in the -mackerel and perch, Fig. 2, Plate IX. There are sometimes parallel bands -at right angles to the above, as in the perch and mackerel; and this is -a common feature, and apparently a very old one, as we find it in the -young of fishes whose adults are without these rib-like marks, such as -the trout and pike. - -It is only necessary to inspect any drawings of fishes to see that their -colouration is on a definite principle, although rather erratic. -Important functional parts, like the gills, fins, and tail, are -generally marked in colour more or less distinctly, as may be seen, for -instance, in our common fresh-water fishes, like the roach and perch. -The line of mucus-secreting glands running along the sides is usually -marked by a dark line. These facts point distinctly to structural -decoration. - - [Illustration: Plate IX. - CHAR AND PERCH.] - -There are in some fishes, like the John Dory, curious eye-like dark -spots, which we cannot refer to a structural origin, though a better -acquaintance with the class might reveal such significance. - -The Amphibia have not been well studied by us, and we must leave them -with the remark that they seem to bear out the view of structural -decoration, as is seen in our English newts. Some are, however, modified -out of all easy recognition. - -_Reptiles._ Among the reptiles, the snakes, Fig. 4, may be selected for -illustration. Snakes are practically little more than elongated -backbones, and are peculiar from the absence of limbs. The colouring -matter does not reside so much in the scales as in the skin beneath, so -that the sloughs do not illustrate the decoration. Hence, we might -expect to find here a direct effect of morphological emphasis. - -The ornamentation of snakes is very similar throughout the class, both -in water and land snakes; as may be seen by Sir W. Fayrer's work on -Venomous Snakes. This ornamentation is of a vertebral pattern, placed -along the dorsal surface, with cross lines, which may represent ribs. - -Where the ribs are wanting, as in the neck, the pattern changes, and we -get merely longitudinal markings. - -In the Python, Fig. 4, there are, near the central line, numerous round -spots, which apparently emphasize the neural processes. There are -diagonal markings on some species which illustrate the development of -colour-spots already alluded to. - -This snake-pattern is very singular and striking. The markings are fewer -in number than the vertebræ, yet their true vertebral character is most -obvious. - -In Snakes, again, we find the dorsal region is darker than the ventral. - -In the Lizards there are patches of colour placed axially, while each -patch covers a number of scales. - -_Birds._ Birds have their whole economy modified to subserve their great -functional peculiarity of flight. - -Immense muscles are required for the downward stroke of the wing, and to -give attachment to these the sternum has a strongly developed keel. To -bring the centre of gravity low, even the muscles which raise the wing -are attached to the sternum, or breastbone, instead of to the dorsal -region, as might be expected; and to brace the wings back a strong -furculum--the merry-thought--is attached. The breast, then, is the seat -of the greatest functional activity in birds, and, consequently, we find -in a vast number of birds that the breast is the seat of vivid colour. - -As many birds are modified for protective purposes, the brightest -species were selected to test our views, namely, the Birds of Paradise -(Paradisea), Humming Birds (Trochilidæ), and Sun Birds (Nectarinidæ). In -these birds it is clear that colour has had full sway, untramelled by -any necessity for modification. - -Nothing is more striking than the mapping out of the surface of these -birds into regions of colour, and these regions are always bounded by -structural lines. - -Take, for instance, _Paradisea regia_. In this bird we find the -following regions mapped in colour:-- - - Sternum brown. - Clavicle yellow. - Pelvis yellow. - Band brown. - Frontal bone black. - Parietal bones green. - Occiput yellow. - -A beautiful ruff emphasizes the pectoral muscles, and the tail -appendages emphasize the share-like caudal vertebræ. - -If we turn to the other species of this genus, we find in _P. Papuana_ -the claret breast suddenly change to green at the furculum; and similar -changes take place in _P. speciosa_, while in _P. Wallacei_ and -_Wilsoni_ this region is decorated with a wonderful apron of metallic -green. - -The region of the furculum is equally well marked in the Toucans and -Sun-birds. - -If now we observe the back of a bird, and view the skeleton with the -wings at rest, we shall find it falls into three morphological tracts. -First, the shoulder, or scapular track; second, the thigh, or pelvic; -third, the tail, or caudal region; and in all these birds the several -tracts are beautifully marked by sudden and contrasted change of colour. -In _P. Wilsoni_ all the tracts are brilliant red, but they are separated -by jet-black borders. In _Nectarinea chloropygia_ the scapular region is -red, the pelvic yellow, and the caudal green. - - [Illustration: Plate X. - SUN BIRDS.] - -In _P. Wilsoni_ we have a wonderful example of morphological emphasis. -The head is bare of feathers, and coloured blue, except along the -sutures of the skull, where lines of tiny black feathers map out the -various bones. - -But morphological emphasis exists everywhere in birds. The -wing-primaries, which attach to the hand, are frequently differently -decorated from the secondaries, which feathers spring from the ulna; and -the spur-feathers of the thumb, or pollux, are different in shape, and -often in colour, from the others, as every fly-fisher who has used -woodcock spur-feathers knows full well. The wing-coverts and -tail-coverts are frequently mapped in colour; and the brain case is -marked by coloured crests. The eye and ear are marked by lines and -stripes; and so we might go on throughout the whole bird. We may remark -that these very tracts are most valuable for the description and -detection of species, and among ornithologists receive special names. - -Now, this distribution of colour is the more remarkable inasmuch as the -feathers which cover the surface--the contour feathers--are not evenly -distributed over the body, but are confined to certain limited tracts, -as shown by Nitzsch; and though these tracts have a morphological -origin, they are rendered quite subsidiary to the colouration, which -affects the whole bird, and not these regions in particular. In fact, -the colouration is dependent upon the regions on which the feathers lie, -and not upon the area from which they spring. In other words, we seem to -have in birds evidence of the direct action of underlying parts upon the -surface. - -In more obscurely coloured birds, and those which seem to be evenly -spotted, close examination shows that even here the decoration is not -uniform, but the sizes and axes of the spots change slightly as they -occupy different regions; as may be seen in Woodpeckers and Guinea-fowl. - -Although the same tone of colour may prevail throughout the plumage, as -in the Argus Pheasant, great variety is obtained by the fusion of spots -into stripes. A symmetrical effect is produced by the grouping of -unsymmetrical feathers; as is so often seen in plants, where irregular -branches and leaves produce a regular contour. - -Sometimes, especially on the breast and back, the feathers of one region -seem to unite so as to form one tract, so far as colour is concerned. -Thus, if in _P. Wilsoni_ the black borders of the dorsal regions were -suppressed, all three areas would be of one hue. This seems to have -been the case in the breast region of Humming Birds, where only the -throat is highly coloured. In the Toucans the breast and throat regions -are often marked with colour; but sometimes the hue is the same and the -boundaries of the regions marked with a band of another colour; if this -boundary band be increased, the regions do not seem so well shown, for -the boundary becomes as broad as the area; yet, in all these cases the -dependence upon regional decoration is manifest. No doubt the few -uniformly coloured birds were derived from species which were once -variously hued; the gradation of colour being lost in transmission. - -_Mammalia._ The axial decoration of the mammalia is very definite, and -nearly all species have a dorsal tract marked with colour. The dark -bands on the back of the horse, ox, and ass, are cases in point. In -nearly every case the dorsal is darker than the ventral surface. - -If we take highly decorated species, that is, animals marked by -alternate dark and light bands, or spots, such as the zebra, some deer, -or the carnivora, we find, first, that the region of the spinal column -is marked by a dark stripe (Figs. 9 & 16); secondly, that the regions of -the appendages, or limbs, are differently marked; thirdly, that the -flanks are striped, or spotted, along or between the regions of the -lines of the ribs; fourthly, that the shoulder and hip regions are -marked by curved lines; fifthly, that the pattern changes, and the -direction of the lines, or spots, at the head, neck, and every joint of -the limbs; and lastly, that the tips of the ears, nose, tail, and feet, -and the eye are emphasized in colour. In spotted animals the greatest -length of the spot is generally in the direction of the largest -development of the skeleton. - -This morphological arrangement can be traced even when the decoration -has been modified. Thus, in the carnivora we have the lion and puma, -which live in open country, with plain skins, the tiger with stripes, an -inhabitant of the jungle, and the leopard, ocelot, and jaguar with -spots, inhabiting the forests. - -But the lion has a dark dorsal stripe, and the nose, etc., are -emphasized in colour, and, moreover, the lion has probably lost its -marked decoration for protective purposes, for young lions are spotted. -The tiger's stripes start from the vertebræ, and still follow the lines -of the ribs. In the tiger the decoration changes at the neck, and on the -head, and the cervical vertebræ are often indicated by seven stripes. -See Fig. 5. - -The markings over the vertebræ are not in continuous lines, as in many -mammals, but form a series of vertebra-like spots. This plan of -decoration is continued even on the tail, which is coloured more on the -upper than on the lower surface. - -The spotted cats have their spot-groups arranged on the flanks in the -direction of the ribs, at the shoulder and haunch in curves, at the neck -in another pattern, on the back of the head in another; and the pattern -changes as each limb-joint is reached, the spots decreasing in size as -the distance is greater from the spine. See Figs. 9-15. - -There is in tigers, and the cat-tribe generally, a dark stripe over the -dental nerve; and the zygoma, or cheek-bone, is often marked by colour. -Even the supraorbital nerve is shown in the forehead, and there are dark -rings round the ears. In dissecting an ocelot at the Zoological Gardens -in 1883, a forked line was found immediately over the fork of the -jugular vein. - -The colouration in these animals seems often to be determined by the -great nerves and nerve-centres, and the change from spots, or stripes, -to wrinkled lines on the head are strikingly suggestive of the -convolutions of the brain, falling, as they do, into two lateral masses, -corresponding with the cerebral hemispheres, separated by a straight -line, corresponding with the median fissure. This is well shown in the -ocelot, Fig. 15, and in many other cats. - -That the nerves can affect the skin has already been pointed out in -Chapter VI., in the case of herpes, and that it can affect colour is -shown in the Hindoo described in the same place. - -So marked, indeed, is this emphasis of sensitive parts that every hair -of the movable feelers of a cat is shown by colour to be different in -function from the hairs of the neck, or from the stationary mass of hair -from which the single longer hair starts. - -In the Badger, Fig. 16, there is a bulge-shaped mass of coloured hair -near the dorsal and lumbar regions, but it is axially placed. The -shoulder and loins are well marked, although in a different manner from -other species. In some species of deer, and other mammalia, there are -white or coloured lines parallel to the spine, and also, as in birds, -spots coalesce and form lines, and lines break up into spots. - -The great anteater has what at first seems an exceptional marking on the -shoulder, but a careful examination of the fine specimen which died at -the Zoological Gardens in 1883, we were struck with the abnormal -character of the scapula, and we must remember that, as Wallace and -Darwin have pointed out, all abnormal changes of the teeth are -correlated with changes in the hair. Moreover the muscles of the -shoulder region are so enormously developed as to render this otherwise -defenceless animal so formidable that even the jaguar avoids an embrace -which tightens to a death-grip. This region is, therefore, precisely the -one we should expect to be strongly emphasized. This being the case, we -have really no exception in this creature. - -Certain mammals are banded horizontally along their sides, thus losing -most of their axial decoration, and this is well shown among the -Viverridæ, and smaller rodents. Now, however conspicuous such animals -may appear in collections, they are in their native haunts very -difficult to detect. In all cases there is a marked dorsal line; and we -suggest that the mature decoration is due to a suppression of the axial -decoration for protective purposes, and a repetition of the dorsal -decoration according to the law before enunciated. Indeed, in one case -we were able to trace this pretty clearly, in the beautiful series of -_Sus vittatus_ in the museum at Leyden. This pig, an inhabitant of Java, -when mature is a dark brown animal, but in the very young state it is -clearly marked in yellow and brown, with a dark dorsal stripe, and -spots, taking the line of the ribs, and over the shoulder and thigh. As -the animal grows older, the spots run into stripes, and it becomes as -clearly banded horizontally as the viverridæ. Finally the dark bands -increase in width, until they unite, and the creature becomes almost -uniformly brown. - -We have not been able to see young specimens of the viverridæ, but a -similar change may there occur, or it may have occurred in former times. -We must also remember that these creatures are long-bodied, like the -weasels, and hence they may have a tendency to produce long stripes. - -In the case of our domestic animals, especially the oxen, the decoration -seems often to have become irregular, but even here the emphasis of the -extremities is generally clearly made out, and that of the limbs can -often be traced. In horses this is better shown, and dappled varieties -often well illustrate the points. Most horses at some time show traces -of spots. - -Sufficient has now been said to point out the laws we believe to have -regulated the decoration of the animal kingdom. The full working out of -the question must be left to the future, but it is hoped that a solid -groundwork has been laid down. - - [Illustration: Plate XI. - LEAVES.] - - - - - CHAPTER XV. - - THE COLOURATION OF PLANTS. - - -The general structure of plants is so simple in comparison with that of -animals that our remarks upon this sub-kingdom need only be short. - -With regard to leaves, especially such as are brightly coloured, like -the Begonias, Caladiums, Coleus, and Anoechtochilus, Plate XI., the -colour follows pretty closely the lines of structure. We have border -decoration, marking out the vein-pattern of the border; the veins are -frequently the seat of vivid colour, and when decolouration takes place, -as in variegated plants, we find it running along the interspaces of the -veins. These facts are too patent to need much illustration; for our -zonale geraniums, ribbon grasses, and beautiful-leaved plants generally, -are now so common that everyone knows their character. When decay sets -in, and oxidation gives rise to the vivid hues of autumn, we find the -tints taking structural lines, as is well shown in dying vine and -horse-chestnut leaves, Fig. 1, Plate XI. This shows us that there is a -structural possibility of acquiring regional colouration. - -We must remember, too, that the negative colouration of these dying -leaves is of very much the same character as the positive colouration of -flowers, for flowers are modified leaves, and their hues are due to the -oxidation of the valuable chlorophyll. - -In leaves the tendency of spots to elongate in the direction of the leaf -is very marked, as may be well seen in Begonia. Fig. 17, drawn to -illustrate another point, shows this partly. When leaves are -unsymmetrical, like the begonias, the pattern is unsymmetrical also. - -Among parallel veined leaves we find parallel decoration. Thus, in the -_Calatheas_ we have dark marks running along the veins. In _Dracæna -ferrea_ we have a dark green leaf, with a red border and tip, the red -running downwards along the veins. This action may be continued until -the leaf is all red except the mid-rib, which remains green. In long -net-veined leaves we may cite _Pavetta Borbonica_, whose dark green -blade has a crimson mid-rib. Of unsymmetrical leaves those in the plate -may suffice. - -When we come to flowers, the same general law prevails, and is generally -more marked in wild than in cultivated forms, which have been much, and -to some extent unnaturally, modified. Broadly speaking, when a flower is -regular the decoration is alike on all the parts; the petals are alike -in size, the decoration is similar in each, but where they differ in -size the decoration changes. Thus, in _Pelargoniums_ we may find all -five petals alike, or the two upper petals may be longer or shorter than -the lower three. In the first case each is coloured similarly, in the -other the colour pattern varies with the size of the petal. The same may -be seen in Rhododendron. - -Where the petals are united the same law holds good. In regular flowers, -like the lilies, the colouration is equal. In irregular flowers, like -the snapdragon and foxglove, the decoration is irregular. In Gloxinia -the petals may be either regular or irregular, and the decoration -changes in concert. - -A very instructive case was noticed by one of us in _Lamium -galeobdolon_, or yellow Archangel. This plant is normally a labiate with -the usual irregular corolla, but we have found it regular, and in this -instance the normal irregular decoration was changed to a regular -pattern on each petal. - -In gamopetalous flowers the line of junction of the petals is frequently -marked with colour, and we know of no case in which a pattern runs -deliberately across this structure line, though a blotch may spread from -it. - -When we remember that flowers are absolutely the result of the efforts -of plants to secure the fertilizing attention of insects, and that they -are supreme efforts, put forth at the expense of a great deal of -vegetable energy--that they are sacrifices to the necessity for -offspring--it does strike us forcibly when we see that even under these -circumstances the great law of structural decoration has to be adhered -to. - - [Illustration: Plate XII. - FLOWERS.] - - - - - CHAPTER XVI. - - CONCLUSIONS. - - -We have now, more or less fully, examined into the system of colouration -in the living world, and have drawn certain inferences from the facts -observed. - -It appears that colouration began--perhaps as a product of digestion--by -the application of pigment to the organs of transparent creatures. -Supposing that evolution be true--and, if we may not accept this theory -there is no use in induction whatever--it must follow that even the -highest animals have in the past been transparent objects. This was -admirably illustrated by Prof. Ray Lankester in a lecture on the -development of the eyes of certain animals, before the British -Association meeting at Sheffield, in which it was shown that the eyes -commenced below the surface, and were useful even then, for its "body -was full of light." - -Granting this, it follows that the fundamental law of decoration is a -structural one. Assuming, as we do, that memory has played a most -important part in evolution, it follows that all living matter has a -profound experience in decorating its organs--it is knowledge just as -anciently acquired, and as perfectly, as the power of digestion. This -colour was produced under the influence of light--so it is even in -opaque animals. - -With a knowledge so far reaching, we might expect that even in opaque -animals the colouring would still follow structural lines, and there -should still be traces of this, more or less distinct. - -This is precisely what we do find; and, moreover, we sometimes get a -very fair drawing of the important hidden parts, even where least -expected, as in a cat's head, a snake's body, a dragon-fly's thorax, a -spider's abdomen, a bird's skull. - -But if animals thus learned to paint themselves in definite patterns, we -might expect that when called upon to decorate _for the sake of beauty_ -certain parts not structurally emphatic, they would adopt well-known -patterns, and hence arose the law of repetition. - -But with wider experience came greater powers, and the necessity for -protection arising, the well-known patterns were enlarged, till an -uniform tint is produced, as in the Java pig, or some repeated at the -expense of others, as in the civets. But so ingrained is the tendency to -structural decoration that even where modification has reached its -highest level, as in the leaf-butterflies, some trace of the plan that -the new pattern was founded on is recognisable, just as the rectangular -basis can be traced in the arabesque ornaments of the Alhambra. - -The pointing out of this great fact has seemed to us a useful addition -to the great law of evolution. It supplements it; it gives a reason why. - -Could he who first saw these points have read these final pages, it -would have lightened the responsibility of the one upon whom the -completion of the work has fallen. But he died when the work was nearly -finished. The investigation is of necessity incomplete, but nothing -bears such misstatements as truth, and though specialists may demur to -certain points, the fundamental arguments will probably remain intact. - - - [Illustration: FINIS.] - - - - - GLOSSARY. - - - ACETABULA. Lat. _acetabulum_, a little vessel. Sucking discs as on - the tentacles of _Physalia_. - - AORTA. Gr. The chief artery. - - CEPHALOTHORAX. Gr. _kephale_, head; _thorax_, chest. The anterior - division of the body in Crustacea and Arachnida, composed of the - amalgamated segments of the head and thorax. - - CILIA. Lat. _cilium_, an eyelash. Microscopic filaments having the - power of vibratory movement. - - C[OE]NOSARC. Gr. _Koinos_, common; _sarx_, flesh. The common stem - uniting the separate animals of compound hydrozoa, &c. - - CORPUSCLE. Lat. _corpusculum_, a little body. Small coloured - bodies, as in the endoderm of hydra, p. 59. - - DIFFERENTIATED. Modified into definite organs, or parts; as - distinct from structureless protoplasm. - - ECTODERM. Gr. _ektos_, outside; _derma_, skin. The internal layer - or skin of the Coelenterata. - - EFFERENT. Lat. _effero_, to carry out. A vessel which carries - fluids out of the body is said to be efferent. - - ENDODERM. Gr. _endon_, within; _derma_, skin. The inner layer or - skin of Coelenterata. _See_ ECTODERM. - - ENDOSARC. Gr. _endon_, within; _sarx_, flesh. The inner layer of - sponges. - - EPIDERMAL. Gr. _epi_, upon; _derma_, skin. Relating to the outer - layer of skin. As applied to colour, surface pigment as distinct - from hypodermal, or deep-seated colour. - - GASTROVASCULAR CANAL. Gr. _gaster_, belly; Lat. _vasculum_, a - little vessel. The canals or vessels in the umbrella (_manubrium_) - of hydrozoa. - - GONIDIA. Gr. _gonos_, offspring; _oidos_, like. Reproductive bodies - in Sea-anemones. - - HYDRANTH. Gr. _hudor_, water; _anthos_, flower. The bodies or - polypes of hydroids which exercise nutritive functions. They were - called polypites by Huxley. - - HYDROPHYLLIA. Gr. _hudor_ and _phyllon_, a leaf. Leaf-like organs - protecting the polypites of hydrozoa. - - HYDROSOMA. Gr. _hudor_ and _soma_, body. The entire organism of a - hydrozöon. - - HYPODERMAL. Gr. _hypo_, beneath; _derma_, skin. In colour, such as - lies beneath the surface, as distinct from epidermal. - - LYTHOCYSTS. Gr. _lythos_, stone, _kystis_, a bladder. Sense organs - in hydroids, consisting of transparent capsules inclosing round - transparent concretions. - - MANUBRIUM. Lat. a handle. The central polypite suspended from the - interior of the umbrella of hydroids. - - MESODERM. Gr. _mesos_, intermediate; _derma_, skin. The middle - layer of sponges, &c. - - MESOTHORAX. Gr. _mesos_ and _thorax_. The middle division of the - thorax in insects, carrying the second pair of legs. - - PERISTOME. Gr. _peri_, about; _stoma_, a mouth. The area - surrounding the mouth in sea-anemones. - - PNEUMATOCYST. Gr. _pneuma_, air; _kystis_ a bladder. The air-sac - contained in the pneumatophore, see below. - - PNEUMATOPHORE. Gr. _pneuma_; _phero_, to carry. The float of - certain hydrozoa (_Physophoridæ_.) - - POLYPITE. Gr. _polus_, many; _pous_, foot. The separate animal or - zöoid of a hydrozöon. _See_ HYDRANTH. - - PROTOPLASM. Gr. _protos_, first; _plasso_, I mould. The jelly-like - matter which forms the basis of all tissues. It is identical with - the _sarcode_ or flesh of protozoa. - - SAC. Lat. _saccus_, a bag, a small cell. - - SARCODE. Gr. _sarx_, flesh; _eidos_, form. The protoplasm of - protozoa, &c., which see. - - SPADIX. Lat. _spadix_, a broken palm branch. In zoology a hollow - process occupying the axis of the generative buds of hydrozoa. - - SPOROSAC. Gr. _spora_, a seed, and _sac_. The body containing the - ova of hydrozoa. - - SOMATIC FLUID. Gr. _soma_, the body. The fluid which contains - digested food, and taking the place of blood, circulates through - the body of hydrozoa. - - TENTACLES. Lat. _tentaculus_, a little arm. The arms or prehensile - organs of Sea-anemones, &c. - - THREAD CELLS. Cells containing an extensible microscopic thread, - possessing stinging properties, common among the _Coelenterata_. - - THORAX. Gr. a breastplate. The chest. - - - - - INDEX. - - - PAGE - - _Abyla_ 63 - - _Acanthometra_ 57 - - _Actinea Cari_, varieties of 66 - - ---- _mesembryanthemum_ 54 - - _Acanthostratus_ 57 - - _Actinozoa_ 51, 52 - - _Æschna_ 77 - - _Agalma breve_ 64 - - _Agrion puella_ 77 - - _Aiptasia mutabilis_ 67 - - Albinism in butterflies 79 - - _Alcyonariæ_ 54 - - Allman, Prof., on Hydroids 59, 60 - - "Alps and Sanctuaries" quoted 36 - - _Amoeba_ 56 - - Amphibia 89 - - _Amphilonche_ 57 - - Andres, Dr., on Hydrozoa 65 - - _Anemonia sulcata_ 67 - - Anemones, Sea 52 - - Animals and Plants, origin of 36 - - ---- classification of 49 - - _Anoechtochilus_ 95 - - Anteater 93 - - _Anthocaris belemia_ 41 - - ---- _belia_ 42 - - ---- _cardamines_ 41, 42 - - ---- _euphemoides_ 43 - - ---- _eupheno_ 42 - - ---- _simplonia_ 42 - - _Apatura iris_ 46 - - ---- larvæ of 81 - - _Arachnida_ 82 - - _Araschnia Levana_ 43, 45 - - ---- _porima_ 43, 45, 79 - - ---- _prorsa_ 43, 45 - - _Arctia_ 69 - - _Arachnocorys_ 57 - - Argus Pheasant 6, 39, 91 - - _Argynnis Lathonia_ 69 - - Armadillo 84 - - Arthropoda, colouration of 85 - - Ascidians 35 - - Automatic habits 9 - - _Arthorybia rosacea_ 64 - - - Badger 93 - - _Begonia_ 95 - - Birds, colouration of 89 - - ---- of Paradise 90 - - _Biston betularia_ 79 - - Black and White, production of 28 - - Blackwell, J., on British Spiders 82 - - _Blatta_ 14 - - Bougainvillea 16 - - Bower Birds 5 - - _Bunodes crassicornis_ 54 - - ---- _gemmaceus_, varieties of 66 - - ---- _rigidus_ 67 - - Burnet Moths 5, 69 - - Butler S., on inherited memory 9, 10, 11, 15 - - ---- on origin of animals and plants 36 - - Butterflies, albinism in 79 - - ---- classification of 74 - - ---- sense organs of 30 - - ---- varieties of 77 - - - _Caladium_ 95 - - _Calathea_ 96 - - _Calycophoridæ_ 63 - - _Carcinus moenas_ 4 - - _Carpocanium_ 57 - - Cats, colouration of 17, 92 - - ---- recognising form 32 - - Caterpillars, colours of 81 - - ---- spiracular markings 22 - - _Cephalopoda_ 87 - - _Cerithium_ 86 - - Char 88 - - Chlorophyll in hydra 59 - - Cicada 77 - - _Cladococeus_ 57 - - Classification of animals 49 - - ---- of butterflies 74 - - _Coelenterata_ 20 - - ---- colouration in 51 - - _Coelodendrum_ 57 - - _Coenonympha davus_ 79 - - ---- _pamphilus_ 79 - - Coenosarc 55 - - _Coleus_ 95 - - Colour and form 32 - - ---- and transparency 53 - - ---- epidermal 72 - - ---- following structure 83, 91 - - ---- hypodermal 53, 73 - - ---- nature of 25 - - ---- of day-and-night flying insects 47, 69 - - ---- opaque 53 - - ---- perception of 5, 23, 25, 32 - - ---- uniform, why rare 28 - - Colouration 3 - - ---- laws of 21, 51 - - ---- of desert animals 4 - - ---- of arthropoda 85 - - ---- of coelenterata 51, 59 - - ---- of insects 68 - - ---- of invertebrata 49 - - ---- of molluscs 85 - - ---- of plants 94 - - ---- of protozoa 51 - - ---- of spiders 82 - - ---- of vertebrata 88 - - ---- sexual 5 - - ---- varieties of 3 - - Contour feathers 91 - - _Conus_ 86 - - _Coppinia arcta_ 60 - - _Corallium rubrum_ 54 - - Corals 54 - - Correlation of teeth and hair 94 - - _Corynida_ 52 - - Cowries 86 - - Crab, shore 4 - - Croton 46 - - Cuttle-fishes 19, 87 - - _Cyllo leda_ 45 - - _Cynthia cardui_ 68 - - _Cypræa_ 86 - - _Cyrtidosphæra_ 57 - - - Dallas, W. S., on butterflies 71 - - _Danais_ 72 - - ---- niavius 30, 80 - - Darwin, C. 1, 2, 5, 9, 11, 14, 45, 47, 94 - - Darwin, Dr. E., cited 37 - - Deer 92 - - Deformity, antipathy to 32 - - _Deilephila Euphorbiæ_ 81 - - ---- _galii_ 81 - - Descent with modification 1 - - Desert animals, colour of 4 - - _Dictyoceras_ 57 - - _Dictyophimus_ 57 - - _Diphyes_ 63 - - Disease, markings in 39, 44 - - Distant, W. L., on Malayan butterflies 80 - - Distinctive Colouration 3 - - Dogs recognising portraits 32 - - _Dracæna ferrea_ 96 - - - Elephant, increase of 2 - - Engelmann on _Euglena_ 34 - - Epidermal colour 72 - - _Eresus cinnabarinus_ 82 - - _Eucecryphalus_ 57 - - _Eucrytidium_ 57 - - _Euglena viridis_ 34 - - Evolution 1-98 - - Eye-spots 45, 47 - - - Fayrer, Sir W., on snakes 89 - - Feathers 91 - - Fishes, colours of 88 - - Foal, stripes on 46 - - _Foraminiferæ_ 56 - - Fuller, W. J., on aquatic larvæ 77 - - - Gamopetalous flowers 96 - - Gegenbaur's "Comparative Anatomy" cited 82 - - General colouration 3 - - _Gloxinia_ 96 - - _Gomphina_ 77 - - _Gonepteryx Cleopatra_ 41, 42 - - ---- _rhamni_ 40, 42 - - Gonophores 52 - - _Grapta interrogationis_ 79 - - _Gregarinidæ_ 56 - - Guinea-fowl 91 - - - Haagen, Dr., on colour 53, 72 - - Habits 8 - - Haeckel, Prof., on _Radiolaria_ 57 - - Hair and teeth, correlation of 94 - - Hawk moths 69 - - Hebrides, colours of insects in 80 - - Heredity 2 - - Herpes 40, 93 - - Heteromorphism 78 - - Higgins, Rev. H. H. 39 - - Hoverer flies 84 - - Humming birds 90, 92 - - Hutchinson, Mr., on herpes 40 - - Huxley, Prof., on hydrozoa 63 - - _Hydra viridis_ 59 - - _Hydrida_ 59 - - Hydrozoa 51, 59 - - Hypodermal colour 53, 72 - - - Identity of offspring and parent 11 - - Identity, personal 10 - - Inherited memory 8 - - Insects, colour in 68, 75 - - - John Dory 89 - - - _Kallima inachus_ 30, 80 - - Kentish Glory Moth 30 - - - _Lamium galeobdolon_ 96 - - Lankester, Prof. Ray, on development of eyes 97 - - Large Copper Butterfly 68 - - Larvæ, colours of 45, 81 - - Laws of emphasis 21 - - ---- exposure 18 - - ---- heredity 2 - - ---- multiplication 2 - - ---- repetition 21, 22 - - ---- structure 18 - - ---- variation 2 - - Leaf-butterfly 16, 30 - - Leidy, Prof., on _Rhizopoda_ 56 - - Leopard 17, 92 - - _Leucophasia diniensis_ 41 - - ---- _sinapis_ 41 - - "Life and Habit" cited 9 - - Light, reflected 26 - - ---- sensibility to 33 - - ---- waves 25 - - _Liminitis sibilla_ 43 - - Lion 17, 92 - - ---- stripes on young 46 - - Lithocysts of hydroids 62 - - _Lucernaria auricula_ 65 - - _Lycæna dispar_ 68 - - _Lycosa agretyca_ 83 - - ---- _allodroma_ 83 - - ---- _andrenivora_ 83 - - ---- _cambria_ 84 - - ---- _campestris_ 83 - - ---- _latitans_ 84 - - ---- _picta_ 84 - - ---- _piratica_ 84 - - ---- _rapax_ 83 - - - Mackerel 88 - - _Mactra_ 86 - - ---- _stultorum_ 87 - - Madrepores 54 - - Mammalia, colouration in 92 - - _Margarita catenata_ 87 - - Measles 39 - - Medusæ 52, 65 - - Melanism in insects 79 - - Meldola, Prof. R., on Melanism 79 - - _Melitæa artemis_ 43 - - ---- _athalia_ 43 - - Mimicry 3, 4 - - Mollusca 21 - - ---- colouration in 85 - - Monstrosities, antipathy to 32 - - _Morphinæ_ 72 - - _Morpho_ 4 - - _Murex_ 86 - - Muscles of insects 71 - - - _Nectarinea chloropygea_ 90 - - Newman, Mr., on varieties of butterflies 77 - - Newts 89 - - Nitzsch on feather-tracts 91 - - Nudibranchs 85 - - _Nymphalidæ_ 74 - - - Oak Egger Moth 30 - - Ocelli 47 - - Ocelot 93 - - _Oliva_ 86 - - Opaque colouring 53 - - Organ-pipe coral 54 - - Origin of animals and plants 36 - - ---- -- species 1 - - Orthopoecilism 78 - - Oxen 94 - - - Painted Lady Butterfly 68 - - Pangenesis 12 - - _Papilio Ajax_ 79 - - ---- _machaon_ 43, 68, 76, 78 - - ---- ---- larva of 81 - - ---- _merope_ 30, 76, 80 - - ---- _nireus_ 14 - - ---- _podalirius_ 43 - - _Paradisea Papuana_ 90 - - ---- _regia_ 90 - - ---- _speciosa_ 90 - - ---- _Wallacei_ 90 - - ---- _Wilsoni_ 90, 91 - - _Pavetta Borbonica_ 96 - - _Pecten_ 86 - - Pelargonium 96 - - Perch 88 - - Personal identity 10 - - _Physalia_ 63 - - ---- _caravilla_ 64 - - ---- _pelagica_ 64 - - ---- _utriculus_ 64 - - _Physophoridæ_ 63 - - Plaice 88 - - Plants and animals, origin of 36 - - ---- colour in 95 - - Pneumatophores 63 - - Portuguese Man o' War 63 - - Protective resemblance 3 - - _Protista_ 34 - - Protozoa 20 - - ---- colouration in 51, 56 - - Python 89 - - - _Radiolaria_ 57 - - Rarity of uniform colour 28 - - Ray Lankester, Prof., on Ascidians 35 - - Red Admiral Butterfly 29 - - Repetition, effects of 8 - - Reptilia, colouration in 89 - - Resemblance, Protective 3 - - _Rhizophora filiformis_ 64 - - _Rhizopoda_ 56 - - Rhododendron 96 - - Ringlet Butterflies, eye-spots of 47 - - Roach 88 - - Romanes, Prof., cited 33, 34 - - - _Satyrus hyperanthus_ 79 - - Scales of insects, structure of 72 - - Scarlet Tiger Moth 5 - - Sea anemones 52 - - ---- ---- colours of 67 - - Seasonal dimorphism 70 - - Sea squirts 35 - - _Segestria senoculata_ 83 - - Selection, sexual 5 - - Self-coloured flowers 28 - - Sense organs of Butterflies 30 - - _Sertularidæ_ 63 - - Sexual colours 4 - - ---- selection 5 - - ---- dimorphism 70 - - Shell, Structure of 85 - - Shore Crab 4 - - Simple variation in Butterflies 77 - - _Siphonophora_ 63 - - Small pox 39 - - Snakes, patterns of 89 - - Sollas, Prof., on Sponges 58 - - Soles 88 - - _Sparassus smaragdulus_ 82 - - Species, origin of 1 - - _Sphæronectes_ 63 - - _Sphingidæ_ 45, 69 - - Spiders, structure and colour of 82 - - Spiracles of larvæ 22 - - _Spondylus_ 86 - - Sponges 57 - - _Spongida_ 57 - - _Spongocyclia_ 57 - - Spots and Stripes 39 - - _Stephanomia amphitridis_ 63 - - Struggle for existence 2 - - Sun-birds 90 - - _Sus vittatus_ 46, 94 - - Sutton, Mr. Bland, on Herpes 40 - - Swallow-tailed Butterflies 68 - - _Syncoryne pulchella_ 62 - - Systems of colouration 51 - - - Teeth and Hair, correlation of 94 - - _Thomisus cinereus_ 82 - - ---- _floricolens_ 82 - - _Thomisus luctuosus_ 84 - - ---- _trux_ 82 - - Thrush, increase of 2 - - Tiger 17, 92 - - ---- Moths 69 - - _Tipula_ 33 - - Toucans 90, 92 - - Transparency and colour 53 - - _Trigonia_ 86 - - _Tubipora musica_ 54 - - _Tubularida_ 59 - - Tylor, A., on Specific change 10 - - - _Vanessa Antiopa_ 76 - - ---- _atalanta_ 29, 43, 69 - - ---- _urticæ_ 77 - - Variation in insects 70 - - ---- law of 2 - - ---- simple, in Butterflies 77 - - _Velella_ 52, 65 - - Vertebrata, colouration of 88 - - _Viverridæ_ 94 - - - Wallace, A. R., on sexual selection 5, 6, 14, 15 - - ---- on colour 29 - - ---- on abnormal structures 94 - - Warning colours 4 - - Wasps 84 - - Weir, J. Jenner, on variation in insects 78 - - Weismann, Dr., on Caterpillars 81 - - Wing of Butterfly, typical 70 - - ---- patterns of 76 - - Woodpecker 91 - - - Yellow Archangel 96 - - - Zebra 92 - - _Zygæna_ 69 - - - [Illustration] - - - - - [Illustration: Fig. 4.--PYTHON. - _Showing vertebra-like markings._] - - [Illustration: Fig. 5.--TIGER. - _The pattern changes at the points lettered._] - - [Illustration: Fig. 6.--TIGER.] - - [Illustration: Fig. 7.--TIGER. - _Showing supra-orbital nerve mark._] - - [Illustration: Fig. 8.--TIGER. - _Showing cerebral markings, and markings over - nerves near the eyes._] - - [Illustration: Fig. 9.--LEOPARD. - _The pattern changes at the points lettered._] - - [Illustration: Fig. 10.--LEOPARD. - _The pattern changes at the points lettered._] - - [Illustration: Figs. 11, 12.--LEOPARDS' HEADS.] - - [Illustration: Fig. 13.--LYNX. - _The colour changes at the points lettered._] - - [Illustration: Fig. 14.--LYNX.] - - [Illustration: Fig. 15.--OCELOT. - _Showing changes of pattern at the joints, &c., - with enlargement of head-pattern._] - - [Illustration: Fig. 16.--BADGER. - _The colour changes at the points lettered._] - - [Illustration: Fig. 17.--BEGONIA LEAF.] - - - - - Transcriber's Notes: - -Variations in spelling, punctuation and hyphenation have been retained -except in obvious cases of typographical error. - -"Haeckel" and "Hæckel" were used interchangeably and have been -standardized to "Haeckel". - -Image tags interrupting paragraphs have been moved. - -Footnotes have been moved to end of chapters. - - - - - - - - -End of Project Gutenberg's Colouration in Animals and Plants, by Alfred Tylor - -*** END OF THIS PROJECT GUTENBERG EBOOK COLOURATION IN ANIMALS AND PLANTS *** - -***** This file should be named 44849-8.txt or 44849-8.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/4/4/8/4/44849/ - -Produced by Chris Curnow, Nicole Henn-Kneif, Tom Cosmas -and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - -Updated editions will replace the previous one--the old editions -will be renamed. - -Creating the works from public domain print editions means that no -one owns a United States copyright in these works, so the Foundation -(and you!) can copy and distribute it in the United States without -permission and without paying copyright royalties. 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