DIMINISHING ENVIRONMENTAL INFLUENCE 327 



cerned with questions of their plumage, and especially with the colora- 

 tion of the same. A good summary of this knowledge is contained in 

 Vernon. 32 



The effects of certain foods on the plumage of birds is well known to bird 

 fanciers. Thus, hemp-seed causes bull-finches and certain other birds to become 

 black. Cayenne pepper mixed with the food changes the yellow color to an 

 orange red. This color change can only be effected by feeding the very young 

 birds; with adults there is no effect whatever. Sauermann found that all races 

 are not equally susceptible to the abnormal diet, some being changed to crimson, 

 others to a beautiful orange, whilst others remain absolutely unaffected. He 

 found also that canaries are not alone in their susceptibility, for on feeding 

 some white Italian fowls, eight weeks old, with the pepper, orange stripes 

 appeared on the breast feathers, and the breast had become red. One other 

 fowl also developed a red breast, but the remaining ten showed no change what- 

 ever. The doses of Cayenne pepper given were enormous (50 gm. daily), so 

 that the conditions were absolutely unnatural. 



More remarkable than these observations are the facts ascertained 

 by A. E. Wallace, and communicated by him to Darwin. Thus he 

 states that 



The natives of the Amazonian region feed the common green parrot (Chrys- 

 otis festiva) with the fat of large Siluroid, fishes, and the birds thus treated 

 become beautifully variegated with red and yellow feathers. In the Malayan 

 archipelago the natives of Gilolo alter in an analogous manner the colors of 

 another parrot, namely, the Lorius garrulus, and thus produce the Lori rajah 

 or King Lory. 



Artificially produced alterations in the pigmentation of American 

 birds are shown by the experiments of C. W. Beebe. 33 These experi- 

 ments demonstrate that the effect of a very humid atmosphere is to 

 increase the dark pigment in the three species studied, namely, the 

 wood thrush, the white-throated sparrow and the inca dove. Beebe 

 mentions that in a state of nature, where the dark forms have been 

 isolated by geographical barriers (and where, of course, natural selec- 

 tion, or other adaptive forces, have been at work for generations), 

 other structural differences are to be found. " With this darkening 

 of the skin structure is frequently correlated a distinction in point of 

 size, either of the body and skeleton as a whole or superficially, as of 

 larger or shorter feathers of the wings or tail." Since Beebe men- 

 tions no structural changes of the body as a result of his artificially 

 produced humidity, one infers that the changes were confined to the 

 pigmentations. 



In the early stages of embryogeny, heat and light, especially heat, 

 affect the rate of development, 34 but there is nothing, as far as I know, 



32 " Variation in Animals and Plants," pp. 293-294. 

 ^Amer. Breeders' Assn., Vol. V., 1909, pp. 392-394. 



34 Morgan, "Exp. Zool.," pp. 261, 262, 459; and Davenport, "Exp. Morph.," 

 p. 459. 



