226 



Biology in America 



to the time of the fall molt the birds were put in a darkened 

 room and their food supply slightly increased. On this regi- 

 men the birds grew fat and lazy and ceased to sing. Most of 

 them passed the winter thus in full summer plumage, but 

 one of the tanagers molted into the winter plumage as a 

 result of a siidden change of temperature. In the spring 

 the birds were brought under normal conditions again and 

 promptly molted into the spring plumage, the winter molt 

 having been entirely suppressed, a beautiful example of 

 environmental control of an hereditary trait. 



The Scarlet Tanager, Male and Female (Right) 



A striking example of sexual difference in birds. The winter dress 

 of the male is similar to that of the female. From Cooke, "Bird 

 Migration," in Bulletin Bureau Biological Survey. 



The Bobolink (Left) 



A bird of many aliases, admired in the North, detested in the South. 

 From a drawing liy Louis Agassiz Fuertes in Cooke, "Bird Migration," 

 Bulletin Bureau Biological Survey. 



The effects of light on the color of animals are clearly 

 marked in some instances, and in others seemingly negligible. 

 The typical fauna of caves comprises animals, which have 

 little or no pigment, and either partly or wholly degenerate 

 eyes. The amphipod Eucrangonyx gracilis occurs both in 

 the open and in caves. In the latter situation its eyes alone 

 are pigmented, while in the former, other parts of the body 



