diff options
| author | nfenwick <nfenwick@pglaf.org> | 2025-03-03 18:01:22 -0800 |
|---|---|---|
| committer | nfenwick <nfenwick@pglaf.org> | 2025-03-03 18:01:22 -0800 |
| commit | 50da17f03d5c6902876d89c725dba240b1fa940a (patch) | |
| tree | a4d5f0f124c3386e7e86e970733a6f774b88cc2c /44849-0.txt | |
| parent | 6630e79d1e601ea516b37a433a06d5cae80c39a5 (diff) | |
Diffstat (limited to '44849-0.txt')
| -rw-r--r-- | 44849-0.txt | 5328 |
1 files changed, 5328 insertions, 0 deletions
diff --git a/44849-0.txt b/44849-0.txt new file mode 100644 index 0000000..0df33f8 --- /dev/null +++ b/44849-0.txt @@ -0,0 +1,5328 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 44849 *** + +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 THE PROJECT GUTENBERG EBOOK 44849 *** |