ORIGIN OF COLOR IN ANIMALS. 99 



Mr. Kicholas Wagner, using an exceedingly sensitive galvanometer, 

 has discovered fixed currents in the wings of butterflies ; and, with 

 the aid of electric currents, has succeeded in producing changes in the 

 color and disposition of their pigments. What part electricity may 

 play in this matter is still, however, unsettled. 



In regard to the effects of feeding, Darwin cites cases of complete 

 changes in the color of birds brought about by modifications of their 

 alimentation. Bullfinches, fed with hemp-seed, turned black. The 

 common green paroquet, fed with the fat of certain fishes, became 

 striped with red and yellow. 



Volumes have been written on the influence of natural selection 

 upon color, and have elucidated the subject so fully that we need not 

 dwell on it at length. The principal aspect in which the influence 

 asserts itself is that in which the prevailing color among animals gives 

 them a kind of resemblance to the ground on which or the medium in 

 which they live, or to the objects by which they are surrounded, so 

 that they are more readily hidden from their enemies. In other cases 

 they are made conspicuous in color or to resemble disagreeable objects, 

 so that their enemies, mistaking them for something else, shall avoid 

 them. Such cases belong to the classes of phenomena which Mr. 

 Wallace has grouped under the designation of protective mimicry. 

 In other cases, certain colors may be associated with peculiarities that 

 render the animal more capable of resisting peculiar conditions to 

 which it may be exposed ; when natural selection, aided by selection 

 by the breeder, may contribute to preserve this color to the exclusion 

 of others. Thus, according to Darwin, in Virginia, black hogs alone 

 can endure a course of feeding consisting largely of the roots of 

 Lachnantes tinctoria / so a race of black hogs became established in 

 that country. 



Much more might be said on this subject. We might consider the 

 phenomena of sexual selection to which male birds largely owe their 

 bright plumage ; the heredity of colors, correlative variations, and the 

 complex and obscure action of domestication ; the action of moisture 

 and of some secreted principles ; and the distribution of colors as 

 related to geographical regions. What I have said has been really 

 only introductory to the subject, and for the purpose of reminding 

 investigators what a full field of work they might find in exhaustively 

 following it up. — Translated for the Popular Science Monthly from 

 the Revue Scientifique. 



