cerned with questions of their plumage, and especially with the coloration of the same. A good summary of this knowledge is contained in Vernon.[1]
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 whatever. 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 (Chrysotis 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.[2] These experiments 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 selection, 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 mentions 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,[3] but there is nothing, as far as I know,
