SOME RESULTS OF OSTRICH INVESTIGATIONS. 25/ 



of the same age the difference is most marked, and no one would 

 hesitate in regarding them as pure Cape birds. Such a result is at 

 least suggestive that the distinctive sizes of the northern and 

 southern ostrich will undergo segregation in the F2 generation^ 

 but further chicks will be necessary before the real nature of the 

 segregation can be determined. 



Colour. 



The skin, or body, colours of the ostrich, as distinct from 

 those of the plumage, vary from the chick to the adult stage, are 

 different in the hen and the cock, and change in the latter with 

 the breeding state. They also vary with the physiological con- 

 dition of the bird, according as the surface of the skin is clean or 

 covered v/ith scurf. When low in condition, the skin becomes 

 dry and scaly, thereby masking the true colours ; but as a higher 

 ])hysiological state is reached, the scurf peels oft' or is preened 

 off, and the true fresh colour is revealed. This is particularly 

 the case at the beginning of the breeding season, when the skin 

 colours are at their brightest. The colour is readily seen on the 

 naked legs and under the wings, around the eyes and beak, and 

 elsewhere by turning aside the overlapping feathers. Chicks of 

 both sexes are practically alike, and even young birds show little 

 distinctioiL The hen remains throughout of the same colour as 

 young birds, but the cock undergoes a change beyond, and in 

 places assumes a brilliant scarlet as the nuptial state is attained. 

 From the chick onwards the colour distinctions between the North 

 African and South African ostriches are strongly marked. 



The red and scarlet colouration of the cocks of both races, 

 as well as the rich dark blue of the Cape bird, are found to be 

 dependent upon the presence of the testes, while the black 

 ])lumage is dependent upon the absence of the ovaries. South 

 African cocks which have been castrated while young never 

 assume the red and scarlet skin colours, but retain the light or 

 dark grey of all young birds and mature hens. ( )n the other 

 hand tlie plumage of castrated cocks attains the normal blackness 

 of the sex. as contrasted with the greyness of the hens, from 

 which it may be inferred that the formation of the black pigment 

 of the feathers is not subject to any influence from the male 

 gonads. Spayed hens retain their ordinary body colour, but the 

 normally grev feathers are found to assume the blackness of the 

 cock, sliowing that ordinarily the secretions from the ovaries 

 exercise an inhibitory influence on the formation of black pigment 

 in the feathers of the hen, though having no action on the skin 

 colour.* 



* Prof. T. II. ^Morgan (Amcy. Nat. (1917) 51) has shown thai the 

 cock bird of the Sebright bantam is "hen-feathered," and has proved 

 experimentally that when castrated a complete change in their plumage 

 occurs, normal cock feathers appearing. He considers that as in the hen, 

 some internal secretion, acting tlirough the gonads, must inhibit the deve- 

 lopment of the secondary sexual characters in the hen-feathered cock. 



