568 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1910. 



plumes do not reach their full size until the next stage or even later. 

 As a result of the highly stimulating conditions of artificial feeding, 

 it is found, however, that the plumes tend to attain maturity at the 

 Juvenal stage, and advance but little afterwards. This is more es- 

 pecially the case in some strains than in others. 



- The Juvenal tail quills of the cock are now white or tinged with 

 light or dark brown ; those of the hen are usually a darker or lighter 

 mottled gray. The ju venal upper and under wing coverts are, like 

 the body feathers, gray or blackish, darker in the cock than in the 

 hen. The small black feathers of the neck and head now disappear 

 to a large extent in both sexes, so that the dark longitudinal bands 

 of the chick are scarcely recognizable. The covering of the head and 

 neck becomes a pale gray, almost white in some strains, and often a 

 pure white ring intervenes between the neck and the body feathers. 



With the Juvenal plumage slight sexual distinctions begin to mani- 

 fest themselves. Generally the body feathers are darker in the cocks 

 than in the hens ; the ventral or under feathers are white in the latter 

 but change to black in the former; the wing quills of the cock are 

 pure white, usually tipped with black, while those of the hens are 

 nearly always tipped or tinged throughout with gray. The plumage 

 distinction between the sexes is, however, by no means so decided 

 at the Juvenal stage as later on, when the true blacks appear in the 

 cock while the body feathers of the hen retain the dark gray or drab. 



ADULT PLUMAGE. 



The adult plumage in the cock ostrich is altogether different from 

 that of the hen; even at a glance the two sexes are conspicuously 

 unlike (pi. 3, fig. 2). The full distinction is reached when the birds 

 are about 2 years old, but great variation occurs, some strains com- 

 pleting their changes much before others. The adult cock bird is 

 characterized by the possession of black body feathers and coverts, 

 the hen by drab body feathers and coverts (pi. 4, fig. 1). The differ- 

 ence may perhaps be better appreciated by saying that the hen retains 

 throughout life the same dull gray color which she had in the juvenal 

 plumage, while the cock passes through the juvenal to a stage where 

 the feathers are black. Both sexes are practically alike in color as 

 far as the juvenal plumage, and the hen retains the somber color 

 throughout life while the cock goes a stage further in which he is 

 more conspicuous. Similar sexual relationships hold in many other 

 animals, the female remaining at an earlier developmental stage 

 which is common to both, while the male assumes another more showy 

 garb, differences which may perhaps have a bearing upon questions 

 of sexual selection and protective resemblance. 



In young cocks there is a marked contrast between the gray or 

 drab feathers of the juvenal plumage and the first black feathers 



