296 



R. M. STRONG. 



appear in the feather germs, and they resemble early stages in 

 the development of the chromatophores which are found in the 

 feather germs of most birds, except that they possess pigment 

 distributing processes. Relatively small and light-colored 

 melanin granules are formed. It is the intention of the writer 

 to discuss these chromatophores more fully in another paper. 



Minute traces of pigment are usually to be found in the 

 plumage of the white bird, especially in the rectrices, but the 

 feathers are practically pure white. 



FIG. 2. Cells from the pigment epithelium of the retina, X 1000. The 

 birds were in strong diffused sunlight when killed so that the light condition existed. 

 A, blond ring-dove cells; B, white ring-dove cells. The peculiar form of the cell 

 processes seems to have been due to the shrinking of the pigment epithelium from 

 the rods and cones layer in the preparations of white ring-dove eyes used for 

 drawing. 



The exposed portions of the eyes as seen in the live bird do not 

 differ much in their general appearance for the two forms. An 

 examination of the entire eye removed from its orbit, however, 

 reveals a great difference in pigmentation. The eye of the white 

 bird shows dark pigment in the iris region only, whereas the 

 whole eye ball is dark in the case of the blond bird. A histological 

 comparison was made with the following results. Spherical 

 granules of what appears to be so-called melanin pigment occur 

 in the iris of both birds in considerable quantities so that this 

 region has a black appearance in fixed preparations. These 

 granules vary greatly in size, the largest being about .0005 mm. 



