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Here too, as with the pupa of Papilio It is evident, however, that these two Nireus, colours such as scarlet or blue, tints have been acquired for concealwhich do not occur in the immediate ment and protection. Looking down environment of the animal, cannot be on the dark back of a fish it is almost produced. Somewhat similar changes invisible, while to an enemy looking of colour occur in some prawns and up from below the light undersurface flat-fish, according to the colour of the would be equally invisible against the bottom on which they rest. This is light of the clouds and sky. Again, very striking in the Chameleon Shrimp the gorgeous colours of the butterflies (Mysis Chamæleon), which is grey when which inhabit the depths of tropical on sand, but brown or green when forests bear no relation to the kind among sea-weed of these two colours. of light that falls upon them, coming Experiment shows, however, that when as it does almost wholly from green blinded the change does not occur, so foliage, dark brown soil, or blue sky; that here too we probably have a and the bright underwings of many voluntary or reflex sense-action. Many moths which are only exposed at night, cases are known among insects in contrast remarkably with the sombre which the same species has a different tints of the upper wings which are tint according to its surroundings, this or less exposed to the various being particularly marked in some colours of surrounding nature. South African locusts which corre- We find, then, that neither the spond with the colour of the soil general influence of solar light and wherever they are found ; while several heat, nor the special action of variously caterpillars which feed on two or more tinted rays, are adequate causes for the plants vary in colour accordingly. wonderful variety, intensity, and comSeveral such changes are quoted by plexity, of the colours that everywhere Mr. R. Meldola, in
meet us in the animal and vegetable Variable Protective Colouring in world. Let us therefore take a wider Insects (Proceedings of the Zoological view of these colours, grouping them Society of London, 1873, p. 153), and into classes determined by what we some of them may perhaps be due to know of their actual uses or special a photographic action of the reflected relations to the habits of their poslight. In other cases, however, it has sessors. This, which may be termed been shown that green chlorophyll the functional or biological classificaremains unchanged in the tissues of tion of the colours of living organisms, leaf-eating insects, and being discern- seems to be best expressed by a diviible through the transparent integu- sion into five groups as follows: ment produces the same colour as that of the food plant.
(1. Protective colours.
a. Of creatures speThese peculiar powers of change of
2. Warning colours. colour and adaptation, are however rare
ing a. and quite exceptional. As a rule there
3. Sexual colours. is no direct connection between the
4. Typical colours,
Plants. colours of organisms and the kind of light to which they are usually The nature of the two first groups, exposed. This is well seen in most Protective and Warning colours, has fishes, and in such marine animals as been so fully detailed and illustrated porpoises, whose backs are always in my chapter on “Mimicry and other dark, although this part is exposed to Protective Resemblances among Anithe blue and white light of the sky mals,” (Contributions to the Theory of and clouds, while their bellies are very Natural Selection, p. 45), that very generally white, although these are little need be added here except a few constantly subjected to the deep blue words of general explanation.
Proor dusky green light from the bottom. tective colours are exceedingly preva
b. Ordefenceless crea.
5. Attractive colours.
lent in nature, comprising those of all the need of protection has played a the white arctic animals, the sandy- very important part in determining coloured desert forms, and the green the actual coloration of animals. birds and insects of tropical forests. The second class — the warning It also comprises thousands of cases of colours -- are exceedingly interesting, special resemblance-of birds to the because the object and effect of these surroundings of their nests, and is, not to conceal the object, but to especially of insects to the bark, leaves, make it conspicuous. To these creaflowers, or soil, on or amid which they tures it is useful to be seen and recog. dwell. Mammalia, fishes, and reptiles, nised, the reason being that they have as well as mollusca and other marine a means of defence which, if known, invertebrates, present similar pheno- will prevent their enemies from attackmena ; and the more the habits of them, though it is generally not suffianimals are investigated,
the more cient to save their lives if they are numerous are found to be the cases in actually attacked. The best examples which their colours tend to conceal of these specially protected creatures them, either from their enemies or consist of two extensive families of from the creatures they prey upon. One butterflies, the Danaidæ and Acræidæ, of the last-observed and most curious comprising many hundreds of species of these protective resemblances has inhabiting the tropics of all parts of been communicated to
me by Sir the world. These insects are generally Charles Dilke. He was shown in large, are all conspicuously and often Java a pink-coloured Mantis, which, most gorgeously coloured, presenting when at rest, exactly resembled a pink almost every conceivable tint and orchis-flower. The Mantis is a carni- pattern; they all fly slowly, and they vorous insect which lies in wait for
never attempt to conceal themselves : its prey, and by its resemblance to a yet no bird, spider, lizard, or monkey flower the insects it feeds on would be (all of which eat other butterflies) ever actually attracted towards it. This touch them. The reason simply is that one is said to fced especially on they are not fit to eat, their juices butterflies, so that it is really a having a powerful odour and taste living trap and forms its own bait ! that is absolutely disgusting to all All who have observed animals, these animals. Now, we see the reason and especially insects, in their native of their showy colours and slow flight. haunts and attitudes, can understand It is good for them to be seen and how it is that an insect which in a recognised, for then they are never cabinet looks exceedingly conspicuous, molested; but if they did not ditler may yet, when alive in its peculiar in form and colouring from other attitude of repose and with its habitual butterflies, or if they flew so quickly surroundings, be perfectly well con- that their peculiarities could not be cealed. We can hardly ever tell by easily noticed, they would be captured, the mere inspection of an animal, and though not eaten would be maimed whether its colours are protective or or killed. As soon as the cause of the not. No one would imagine the ex- peculiarities of these butterflies was quisitely beautiful caterpillar of the recognised, it was seen that the same Emperor-Moth, which is green with explanation applied to many other pink star-like spots, to be protectively groups of animals. Thus bees and coloured ; yet when feeding on the wasps and other stinging insects are heather it so harmonises
the showily and distinctively coloured; foliage and flowers as to be almost in
many soft and apparently defenceless visible. Every day fresh cases of pro- beetles, and many gay-coloured moths, tective colouring are being discovered were found to be as nauseous as the even in our own country, and it is above-named butterflies; other beetles, becoming more and more evident that whose hard and glossy coats of mail
render them unpalatable to insect- purpose it would be necessary that eating birds, are also sometimes they should have the same colours, showily coloured; and the same rule form, and habits. Strange to say, was found to apply to caterpillars, all wherever there is an extensive group the brown and green (or protectively- of directly-protected forms (division a coloured species) being greedily eaten of animals with warning colours), there by birds, while showy kinds which are sure to be found a few otherwise never hide themselves—like those of defenceless creatures which resemble the magpie-, mullein, and burnet
them externally so as to be mistaken moths were utterly refused by in- for them, and which thus gain protecsectivorous birds, lizards, frogs, and tion as it were on false pretences, spiders. (Contributions to Theory of (division b of animals with warning Natural Selection, p. 117.) Some few colours). This is what is called “mimicanalogous examples are found among ry," and it has already been very fully vertebrate animals. I will only mention treated of by Mr. Bates (its discoverer), hero a very interesting case not given by myself, by Mr. Trimen, and others. in my
former work. In his delightful Here it is only necessary to state that book entitled The Naturalist in Nicar- the uneatable Danaidæ and Acræidæ agua, Mr. Belt tells us that there is
are accompanied by a few species of in that country a frog which is very other groups of butterflies (Leptalidæ, abundant, which hops about in the Papilios, Diademas, and Moths) which day-time, which never hides himself, are all really eatable, but which escape and which is gorgeously coloured with attack by their close resemblance to red and blue. Now frogs are usually some species of the uneatable groups green, brown, or earth-coloured, feed found in the same locality. In like mostly at night, and are all eaten by manner there are a few eatable beetles snakes and birds. Having full faith which exactly resemble species of unin the theory of protective and warn- eatable groups, and others which are ing colours, to which he had himself soft, imitate those which are uneatable contributed some valuable facts and through their hardness. For the same observations, Mr. Belt felt convinced reason wasps are imitated by moths, that this frog must be uneatable. He and ants by beetles; and even poisontherefore took one home, and threw it ous snakes are mimicked by harmless to his ducks and fowls; but all refused snakes, and dangerous hawks by deto touch it except one young duck, fenceless cuckoos. How these curious which took the frog in its mouth, but imitations have been brought about, dropped it directly, and went about and the laws which govern them, have jerking its head as if trying to get rid been discussed in the work already of something nasty. Here the un- referred to. eatableness of the frog was predicted The third class -Sexual Colours from its colours and habits, and we comprise all cases in which the colours can have no more convincing proof of of the two sexes differ. This difference the truth of the theory than • such is very general, and varies greatly in previsions.
amount, from a slight divergence of tint The universal avoidance by car- up to a radical change of coloration. nivorous animals of all these speci- Differences of this kind are found ally protected groups, which are thus among all classes of animals in which entirely free from the constant per- the sexes are separated, but they are secution suffered by other creatures much more frequent in some groups not so protected, would evidently than in others. In mammalia, reptiles, render it advantageous for any of and fishes, they are comparatively rare these latter which
were subjected and not great in amount, whereas to extreme persecution to be mis- among birds they are very frequent taken for the former, and for this and very largely developed. So among insects, they are abundant in butterflies, male are represented by red on the while they are comparatively uncommon female; and in several species of the in beetles, wasps, and hemiptera. genus Epicalia, orange bands in the
The phenomena of sexual variations male are replaced by blue in the of colour, as well as of colour generally, female, a similar change of colour as are wonderfully similar in the two in the small parrot above referred to. analogous yet totally unrelated groups For fuller details of the varieties of birds and butterflies; and as they of sexual coloration we refer our both offer ample materials, we shall readers to Mr. Darwin's Descent of confine our study of the subject chiefly Man, chapters x. to xviii., and to to them. The most common case of chapters iii. iv. and vii. of my Contridifference of colour between the sexes, butions to the Theory of Natural Selection. is for the male to have the same The fourth group of Typicallygeneral hue as the females, but deeper coloured animals—includes all species and more intensified; as in many which are brilliantly or conspicuously thrushes, finches, and hawks ; and coloured in both sexes, and for whose among butterflies in the majority of particular colours we can assign no our British species. In cases where function or use.
It comprises an imthe male is smaller the intensification mense number of showy birds, such of colour is especially well pronounced, as Kingfishers, Barbets, Toucans, as in many of the hawks and falcons, Lories, Tits, and Starlings; among and in most butterflies and moths in insects most of the largest and handwhich the coloration does not mate- somest butterflies, innumerable brightrially differ. In another extensive coloured beetles, locusts, dragon-flies, series we have spots or patches of and hymenoptera; a few mammalia, vivid colour in the male which are as the zebras; a great number of represented in the female by far less marine fishes; thousands of striped brilliant tints or are altogether want- and spotted caterpillars; and abuning; as exemplified in the gold-crest dance of mollusca, star-fish, and other warbler, the green woodpecker, and marine animals. Among these we most of the orange-tip butterflies have included some, which like the (Anthocharis). Proceeding with our gaudy caterpillars have warning survey we find greater and greater colours ; but as that theory does not differences of colour in the sexes, till explain the particular colours or the we arrive at such extreme cases as varied patterns with which they are some of the pheasants, the chatterers, adorned, it is best to include them tanagers, and birds-of-paradise, in also in this class. It is a suggestive which the male is adorned with the fact, that all the brightly coloured most gorgeous and vivid colours, while birds mentioned above build in holes the female is usually dull brown, or or form covered nests, so that the olive green, and often shows no ap- females do not need that protection proximation whatever to the varied during the breeding season, which I tints of her partner. Similar pheno- believe to be one of the chief causes mena occur among butterflies; and in of the dull colour of female birds when both these classes there are also a their partners are gaily coloured. considerable number of cases in which This subject is fully argued in my both sexes are highly coloured in a Contributions, &c., chapter vii. different
way. Thus many woodpeckers have the head in the male As the colours of plants and flowers red, in the female yellow; while some are very different from those of animals parrots have red spots in the male, both in their distribution and functions, replaced by blue in the female, as in it will be well to treat them sepaPsittacula diopthalmu. In many South rately: we will therefore now conAmerican Papilios green spots on the sider how the general facts of colour
here sketched out can be explained. the sensation of all the varied colours We have first to inquire what is and tints we are capable of perceiving. colour, and how it is produced; what When all the different kinds of rays is known of the causes of change of reach us in the proportion in which colour ; and what theory best accords they exist in the light of the sun, they with the whole assemblage of facts. produce the sensation of white. If
The sensation of colour is caused the rays which excite the sensation by vibrations or undulations of the of any one colour are prevented from etherial medium of different lengths reaching us, the remaining rays in and velocities. The whole body of combination produce a sensation of vibrations caused by the sun is termed colour often very far removed from radiation, and consists of sets of waves white. Thus green rays being abwhich vary considerably in their di- stracted leave purple light; blue, mensions and their rate of vibration, orange - red light; violet, yellowish but of which the middle portion green light, and so on.
These pairs only is capable of exciting in us sen- are termed complementary colours. sations of light and colour. Begin- And if portions of differently coloured ning with the largest and slowest rays lights are abstracted in various degrees, or wave-vibrations, we have first those we have produced all those infinite which produce heat-sensations only; gradations of colours, and, all those as they get smaller and quicker, we varied tints and hues which are of perceive a dull red colour ; and as the such use to us in distinguishing exwaves increase in rapidity of vibration ternal objects, and which form one and diminish in size, we get succes- of the great charms of our existence. sively sensations of orange, yellow, Primary colours would therefore be green, blue, indigo, and violet, ali as numerous as the different wavefading imperceptibly into each other. lengths of the visible radiations if Then come more invisible rays, of we could appreciate all their differshorter wave-length and quicker vi- ences, while secondary or compound bration, which produce, solely or colours caused by the simultaneous chiefly, chemical effects. The red action of any combination of rays of rays, which first become visible, have different wave-lengths must be still been ascertained to vibrate at the rate more numerous. In order to account of 458 millions of millions of times in for the fact that all colours
to a second, the length of each wave being us capable of being produced by comsobooth of an inch ; while the violet binations of three primary coloursrays, which last remain visible, vibrate red, green, and violet—it is believed 727 millions of millions of times per that we have three sets of nerve fibres second, and have a wave-length of in the retina, each of which is capable 81318th of an inch. Although the of being excited by all rays, but that waves vibrate at different rates, they one set is excited most by the larger are all propagated through the ether or red waves, another by the medium with the same velocity (192,000 miles or green waves, and the third set per second), just as different musical chiefly by the violet or smallest waves sounds, which are produced by waves of light; and when all three sets are of air of different lengths and rates excited together in proper proportions of vibration, travel at the same rate, we see white. This view is supported so that a tune played several hundred by the phenomena of colour-blindness, yards off reaches the ear in correct which are explicable on the theory time. There are, therefore, an almost that one of these sets of nerve-fibres infinite number of different colour- (usually that adapted to perceive red) producing vibrations, and these may has lost its sensibility, causing all be combined in an almost infinite colours to appear as if the red rays variety of ways, so as to excite in us were abstracted from them. It is