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TEE POPULAR SCIENCE MONTELY.— SUPPLEMENT. 



to the rapidity of their motion, and when startled 

 they dart away with the rapidity of a flash of 

 light. Such active creatures would not be an 

 easy prey to any rapacious bird ; and if one at 

 length was captured, the morsel obtained would 

 hardly repay the labor. We may be sure, there- 

 fore, that they are practically unmolested. The 

 immense variety they exhibit in structure, plu- 

 mage, and color, indicates a high antiquity for the 

 race, while their general abundance in individuals 

 shows that they are a dominant group, well adapt- 

 ed to all the conditions of their existence. Here 

 we find everything necessary for the development 

 of color and accessory plumes. The surplus vital 

 energy shown in their combats and excessive ac- 

 tivity has expended itself in ever-increasing de- 

 velopments of plumage, and greater and greater 

 intensity of color, regulated only by the need for 

 specific identification which would be especially re- 

 quired in such small and mobile creatures. Thus 

 may be explained those remarkable differences of 

 color between closely-allied species, one having a 

 crest like the topaz, while in another it resembles 

 the sapphire. The more vivid colors and more 

 developed plumage of the males, I am now in- 

 clined to think, may be wholly due to their greater 

 vital energy, and to those general laws which 

 lead to such superior developments even in do- 

 mestic breeds ; but in some cases the need of 

 protection by the female while incubating, to 

 which I formerly imputed the whole phenome- 

 non, may have suppressed a portion of the orna- 

 ment which she would otherwise have attained. 



Another real though as yet inexplicable cause 

 of diversity of color is to be found in the influ- 

 ence of locality. It is observed that species of 

 totally distinct groups are colored alike in one 

 district, while in another district the allied species 

 all undergo the same change of color. Cases of 

 this kind have been adduced by Mr. Bates, by 

 Mr. Darwin, and by myself, and I have collected 

 all the more curious and important examples in my 

 "Address to the Biological Section of the British 

 Association'' at Glasgow in 18*76. The most 

 probable cause for these simultaneous variations 

 would seem to be the presence of peculiar ele- 

 ments or chemical compounds in the soil, the 

 water, or the atmosphere, or of special organic 

 substances in the vegetation ; and a wide field is 

 thus offered for chemical investigation in connec- 

 tion with this interesting subject. Yet, however 

 we may explain it, the fact remains, of the same 

 vivid colors in definite patterns being produced in 

 quite unrelated groups, which only agree, so far 

 as we yet know, in inhabiting the same locality. 



Let us now sum up the conclusion at which 

 we have arrived, as to the various modes in which 

 color is produced or modified in the animal king- 

 dom. 



The various causes of color in the animal 

 world are, molecular and chemical change of the 

 substance of their integuments, or the action on 

 it of heat, light, or moisture. It is also produced 

 by interference of light in superposed transpar- 

 ent lamellae, or by excessively fine surface striae. 

 These elementary conditions for the production 

 of color are found everywhere in the surface- 

 structures of animals, so that its presence must be 

 looked upon as normal, its absence as exceptional. 



Colors are fixed or modified in animals by nat- 

 ural selection for various purposes : obscure or 

 imitative colors for concealment — gaudy colors 

 as a warning — and special markings either for 

 easy recognition by strayed individuals females, 

 or young, or to direct attack from a vital part, as 

 in the large, brilliantly-marked wings of some but- 

 terflies and moths. 



Colors are produced or intensified by pro- 

 cesses of development — either where the integu- 

 ment or its appendages undergo great extension 

 or modification, or where there is a surplus of 

 vital energy, as in male animals generally, and 

 more especially at the breeding-season. 



Colors are also more or less influenced by a 

 variety of causes, such as the nature of the food, 

 the photographic action of light, and also by 

 some unknown local action probably dependent on 

 chemical peculiarities in the soil or vegetation. 



These various causes have acted and reacted 

 in a variety of ways, and have been modified by 

 conditions dependent on age or on sex, on compe- 

 tition with new forms, or on geographical or cli- 

 matic changes. In so complex a subject, for 

 which experiment and systematic inquiry have 

 done so little, we cannot expect to explain every 

 individual case, or solve every difficulty; but it 

 is believed that all the great features of animal 

 coloration and many of the details become expli- 

 cable on the principles we have endeavored to 

 lay down. 



It will perhaps be considered presumptuous 

 to put forth this sketch of the subject of color 

 in animals, as a substitute for one of Mr. Dar- 

 win's most highly elaborated theories — that of 

 voluntary or perceptive sexual selection; yet I 

 venture to think that it is more in accordance 

 with the whole of the facts, and with the theory 

 of natural selection itself: and I would ask such 

 of my readers as may be sufficiently interested in 

 the subject to read again chapters xi. to xvi. of 



