298 R. M. STRONG. 



2, B). These were observed with difficulty when a 1.5 mm. oil 

 immersion objective and a No. 6 Zeiss ocular were employed. 

 The microscopic picture which one of these pigment epithelium 

 cells in the eye of the white bird presents, so far as its contained 

 pigment is concerned, suggests strongly the appearance of a 

 developing feather-germ chromatophore in a very early stage 

 when pigment first appears. Various stages in the development 

 of feather-germ chromatophores are figured by me in another 

 paper (Strong, '02, Plate 6, note Fig. 30, especially). 



The nestlings are decidedly different, even at hatching (see 

 Fig. 3). It will be noticed that the down plumage of the white 

 bird is much scantier than that of the blond dove nestling, and 

 it is also somewhat whiter than the yellowish-white down of the 

 blond nestling. The skin color is very different, though the 

 contrast does not appear in the photograph which was used for 

 making Fig. 3. The blond nestling has a rather dark skin which 

 is about No. 93, whereas the white nestling has a light flesh- 

 colored skin about No. 53C. The color of the latter is about 

 that of the beak of the adult white bird. 



The blond ring-dove seems to be somewhat more vigorous 

 than the white ring-dove, and its voice is stronger. Professor 

 Whitman was especially impressed with these points of difference. 

 Unfortunately, no precise data for a comparison of the relative 

 vigor of the two forms are at hand, and the above statements are 

 based mostly on general impressions. The comparison for voice 

 is easier to make as this is distinctly different in the two birds. 



Melanin pigment appears in the iris region earlier in the blond 

 nestlings than in the white birds. Thus, when the eyes have 

 just become fully open, about one week after hatching, the 

 whole visible eye in the live blond bird appears black. The 

 white ring-dove nestling, on the other hand, shows only a dusky 

 ring about the pupil, and a considerable amount of the eye still 

 appears pink. This phenomenon will be referred to again in 

 connection with the discussion of the observations which have 

 been made by Miss Durham on canaries. 



White ring-dove stock is not easy to obtain, and the birds are 

 expensive. It is a curious fact that I found it hard to get 

 female white ring-doves. Some of the stock both of blonds and 

 of whites was imported. 



