ANIMAL COLOURING.
THE conclusions of naturalists as to the laws which govern the colouring of animals must, it seems, be modified. There is no reason, however, to fear any loss of interest in one of the prettiest and most attractive sides of natural history. The collection and comparison of the wonderful analogies in colour between animals and their environment, and between one animal and another, will still be guided by the leading principles which Bates and Wallace detected ; and the delight and surprise with which the non-scientific world welcomed those discoveries need neither be regretted nor diminished. But without wishing to grudge one iota of the praise awarded to explanations, the dexterity and aptness of which would alone entitle them to admiration, it is still possible to doubt whether some of the minor hypotheses framed to account for facts which seemed to stand outside the explanation of colour mimicry by the general law of the survival of the fittest, are not almost too ingenious. The fascination of the subject is so great that it seems to develop an over-keenness of scientific insight. The facts of resemblance themselves are so wonderful, and the contrast between the colours of the sexes in birds so startling, that the temptation to make a great principle like that of natural selection fit the exact requirements of each case, and to explain the complexity of Nature in a sentence, is almost irresistible. It is quite possible that the principle of natural selection, which gives a perfect explanation of the wonderful phenomena of "protective mimicry," may also be the master-key to the remaining problems of animal hues. The chief difficulties which remain, after accounting for protective coloration, are, first, the extraordinary differences between the tints and plumage of male and female in many birds ; and, secondly, the conspicuous colours of certain creatures by which the at- tention of their enemies must necessarily be attracted. The first of these obvious difficulties has been explained by what is called "sexual selection," which is an auxiliary to the general law of natural selection. The female pheasants, or birds of paradise, or pigeons, as the case may be, by an enduring good taste in choosing for their mates those with the brightest plumage and finest wattles and spurs, have played their part in the general scheme of evolution so well, that their progeny have in time• developed all the beauties which they now possess. That theory is obviously quite consistent with the general law. It accounts logically in part, if not entirely, for the perilous beauties of the stronger sex. But there are creatures in gorgeous attire for which "sexual selection" could give no justification.— caterpillars, for instance, which run additional risks by their conspicuous hues. "That," said the naturalist, "is in order to advertise their inedible qualities !" "They require," writes Mr. Wallace, "some signal, or danger flag, which shall serve as a warning to would-be enemies not to attack them, and they have usually obtained this in the form of conspicuous or brilliant coloration, very distinct from the protective tints of the defenceless animals allied to them." There is one obvious objection to this explanation. It is really too clever. It fits the case so perfectly that, in the absence of further experi- ment and observation, one is reluctantly obliged to pause before yielding entirely to such a brilliant surmise, and to welcome the note of warning which Mr. Beddard, the Prosector of the Zoological Society, utters in his admirable work on "Animal Coloration." It is evident, from the space given to the two points of "Sexual Selection" and "Warning Colours" in this work, which aims only at furnishing a general notion of the facts and theories relating to animal coloration, that room exists for doubt as to the value to be attached to either theory. The contribution which Mr. Beddard makes towards solving the difficulty is threefold. He presents as alternatives to the theories of sexual selection and warning coloration, the ingenious speculations of Mr. Stoltzman and Dr. Eiaig, neither of which have yet found their way into works of a popular character; and he gives an account of numerous and careful experiments made at the Zoo, with insects of brilliant colouring and reputed evil flavour, as food for birds and reptiles. No care or pains was omitted to get at the truth of these supposed instances of warning colour- ing. No augurs, with the purest motives to guide their interpretation of the omens, ever watched the feeding of the sacred chickens in the Capitol with a more ardent desire to mark the real appetite of the prophetic fowls, than did Mr. Beddard and his predecessors, in observing the practical results of "warning coloration" when making trial of the birds at the Zoo. But the list of experiments does not give any clear line of refusal or acceptance between the "pro- tectively coloured" insects and their more sober relations, and Mr. Beddard's conclusion is that "the experiments which have been made might be taken to prove anything." That is, so far, disappointing. But it is probable that with time and patience a body of evidence will be accumulated which will throw more light on the vexed question of the palatability of these gaudy insects or reptiles. Meantime, the discoveries of Dr. Eisig, to which Mr. Beddard introduces us, throw light on the question from a different point of view. If his surmises are confirmed, the fact will be additional evidence in favour of that minute and laborious specialisation which so often goes without reward. His researches were devoted to the history of a small group of sea-worms. One of these he found living parasitically upon a marine sponge in the Bay of Naples. The sponge was of a yellow colour, caused by the presence of small particles of colouring-matter. The worm was of the same colour, with bright orange spots, and the pigment which coloured the sponge was found to be the same which coloured the worm, having been simply transferred from the tissues of the sponge to the skin of the worm, after going through part of the alimentary canal. Dr. Eisig is of opinion that the " pigments " so transferred from the alimentary canal to the skin is itself the cause of the creature being distasteful, which suggests the conclusion that the brilliant colour—that is, the secretion of a quantity of colouring-matter —has itself caused the inedibility of species, rather than that the inedibility has made necessary the production of bright colour as an advertisement. "This explanation," Mr. Beddard remarks, 4' is not entirely contrary to the views of Wallace, Poulton, and others; for wa may still suppose that the bright colours are actually 'warning' colours, although they have not been evolved for this purpose." But the weakness, as well as the attraction, of the unmodified theory really lies in the supposi- tion of the creation in the creature of colour, for the express purpose of advertisement. The modest conjecture of Dr. Eisig transfers the explanation to safer ground.
The mode by which, in the simple organisms which he observed, the colour was transferred from the food to the feeder, also suggests the existence of some simple and natural relation between the tints in the skin, or hair, and external conditions of food and temperature, to account for the strange changes of colour to suit outside conditions in animals exposed to the rigours of a northern winter. The mountain hare of Ireland does not always change its colour to white in winter, though in the colder climate of Scotland and Norway the change is the rule. So the Arctic fox seems always to be " bleached " in the extreme north, though often retaining its darker dress throughout the year when further south. Yet, exactly the same effects are found in connection with want of food as with want of warmth. The rats in a large iron ship which was recently wrecked off the coast of Northumberland, and remained stranded for many weeks without connection with the shore, turned quite white ; a change due apparently to starvation.
In strong contrast with the modifications of the part played by evolution in animal colouring, suggested by Dr. Eisig, is the alternative which Mr. Stoltzmann proposes to the theory of sexual selection. It is not a change which will flatter the masculine imagination. Contrasted with the view which accounted for the predominance of male strength, and in some cases of masculine beauty, over the weaker sex by a long course of discerning feminine selection, it has an unconscious irony. Going quite outside the merits of the male sex per se, Mr. Stoltzmann weighs its worth in view of the survival of a species. So considered, an excess of males is an evil, which the law of natural selection is under obligations to remedy. The tendency of nature is to produce a superabundance of males, observations on the origin of sex having shown that the per-centage of male births among birds is greater than that of females. Further inquiries into the influence of nutrition on sex go to show that badly nourished eggs produce males, while well-nourished eggs produce females ; and scarcity of food is a more common condition than its abundance. The fine feathers which "make line birds," have therefore been given to the males with a view to exposing them to the attacks of their enemies, and so reducing their numbers, always—be it observed—in accordance with the law of the survival of the
fittest, but by a curiously different line of argument from that which lent its weight to the theory of sexual selection. Probably neither the one nor the other should stand alone ; nor is this result to be feared. Bigotry seems almost unknown to the spirit of the natural history research of to-day ; the only danger of the open mind °flits followers is in the con- structive ingenuity of theory which it seems to foster.
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