December 17, 1886.1 



SCIENCE. 



561 



tion from the animals that prey upon them, and 

 to approach their own prey unobserved. The most 

 striking characteristic of natural scenery is its 

 color. Accordingly we find that protective color- 

 ing is the most widely distributed mode of mim- 

 icry, though the forms of natural objects are not 

 infrequently imitated by animals. In a general 

 way the animals in cold climates are more liable to 

 be white, like the ice and snow among which they 

 live, while those of tropical habitat present the 

 wealth of color for which southern scenery is 

 famous. The animals of the desert are quite gen- 

 erally of a sandy appearance, and many marine 

 animals of a limpid, transparent tint. To account 

 for this general correspondence between climate 

 and color, the direct action of sunlight has been 

 brought in as a sufficient cause. But apart from 

 the fact that this cause has little explanatory 

 power, it is inconsistent w^ith the fact that many 

 very tamely colored species abound near the 

 equator, and attractive color is not infrequent in 

 northern forms of animal life. Local influences 

 are obviously of great importance. The theory 

 that a direct photo-chemical action takes place, is 

 in some instances undoubtedly true. Caterpillars, 

 in passing into the chrysalis stage, have been ob- 

 served to spin a dusky red cocoon when on a brick 

 wall, a green one when on a twig, or a white one 

 when on a white fence-paling. In these cases the 

 change of color has been observed to take place 

 within the few hours of spinning the cocoon, and 

 is probably not analogous with the usual origin of 

 protective coloring. In such unique cases as the 

 chameleon, when the change of color is under 

 voluntary control, the imitation of the environ- 

 ment is impossible if the creature be blinded. 

 But, apart from these exceptional cases, the only 

 sufficient explanation of color in the animal world 

 is, that it must be a useful trait. In what way it 

 is useful has already been stated. It is impossible 

 to convey in a few words the cumulative effect 

 of the instances of imitative coloring which Dr. 

 Wallace presented. The stripes of the tiger, re- 

 sembling the strong contrasts of light and shade 

 caused by the shadow of dry grasses under a burn- 

 ing sun ; the remarkable list of caterpillars aping 

 the tint of the petals, and the curl of the tendrils, 

 of the flowers and plants on which they live ; and, 

 more wonderful still, the leaf-butterfly of India, 

 which even has the pink circles due to fungi on 

 the leaves, which it imitates so closely that the 

 lecturer had to point out on the screen which were 

 leaves and which were butterflies, — these and 

 many more give evidence of the great role that 

 color plays in nature. And the evidence was still 

 more remarkable, because it was largely taken 

 from a work written many years before Darwin- 



ism and natural selection were mucE thought 

 of. 



Dr. Wallace next called attention to the facts that 

 certain exceptions to this color-adaptation were 

 apparent only, and that color had also other fxmc- 

 tions. The raven, for example, though living in 

 the highest latitudes, is entirely black. But it is 

 to be noted that there the raven is not preyed upon, 

 and that its own prey is dead matter : hence it 

 has no need of protection, and acquires no color- 

 adaptation. 



Again : color is sometimes assumed as a means 

 of CKciting terror in an attacking enemy. Certain 

 harmless caterpillars have acquired the reputation 

 of being deadly on account of such variegated ap- 

 pendages. Finally, Dr. Wallace pointed out the 

 use of color as a means of recognition. The fact 

 that a rabbit, when pursued, raises its tail, and 

 shows its conspicuous white under surface, seems 

 the opposite of a useful act. But by this means it 

 is enabled to recognize its fellows, and run 

 straight to its burrow, with the white tails of the 

 others as a guide. And it often happens that 

 defenceless animals, whose only defence is in 

 flight, possess similar marks for recognizing one 

 another. 



In his third lecture. Dr. Wallace continued the 

 discussion of color in the animal world with 

 special reference to the facts of animal mimicry. 

 Color is a normal feature of animal life, and it 

 will be absent or subdued only when it is kept 

 down by outside influences. For example : those 

 insects that are strong, or protected by a sting, are 

 very apt to be showy and conspicuous. They 

 can afford to be so, because their hard shell (as in 

 beetles) or the sting (as in bees and wasps) is af suffi- 

 cient protection against attack. 



A very peculiar and yet widely current mode of 

 protection is by becoming distasteful and inedible 

 to the attacking animal. A very large class, 

 especially of tropical, butterflies have acquired an 

 extremely disagreeable taste, so that birds and 

 other insectivorous creatures soon learn to avoid 

 them. And the remarkable point is, that such 

 insects are almost invariably conspicuously marked 

 (it is evidently well that they should be), and are 

 usually slow of flight and without other protec- 

 tion. The direct experiment has been tried by 

 Mr. Belt, of feeding birds with these insects, and 

 they are invariably refused. In beetles the same 

 phenomena occur. A great many species with a 

 soft shell, that invites attack, are protected by 

 their inedibility, and are usually lustrous and 

 bright. A tame monkey refused one of these 

 beetles at once, though greedily eating all others. 



We see, then, that the acquisition of certain 

 superficial forms and markings will be a protec- 



