J. E. DUKRDKN IfK] 



C0IX)lTR. 



The 8kin or body colours of the oHtrich, jus <liHtinct from those of the 

 plunmgi^, vary from the chick to the julult sta^e, an- (iirt'ereiit in the hen 

 ami the cock, am! change in the latti-r with the breeding' stjite. They 

 also vary with the physiolo^icnl condition of the bird, m-cordin^' as the 

 surfiwe of the skin is clean or covered with scMirf. When low in con- 

 <iition the skin bec<uues dry and scaly, thereby masking the true coiotii-s ; 

 but lis a higher physiological state is reached the scurf" peels off or is 

 preeniMi oft', and the true fresh colour is n^vealed. This is particularly 

 the Cixse at the beginning of the breeding season when the skin coloui-s 

 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 

 practiadly alike and even young birds show little distinction. The hen 

 remains throughout of the same colour us young birds, but the cock 

 undergoes a change beyond, and in places assumes a brilliant scarlet as 

 the nuptial state is attjiined. From the chick onwards the colour dis- 

 tinctions between the North African and South African ostriches are 

 strongly marked. 



The red and sciirlet 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 plumage 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. On the 

 other hand the 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 grey feathers are 

 found to assume the blackness of the cock, showing 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. H. Morgan, Amer. Nat. \o\. li. Sept. 1917, in the case of tlie cock bird of 

 the Sebright bantam which is "heu-feathered," has proved experimentally that when 

 castrated a complete change in the plumage occurs, normal cock feathers appearing. He 

 considers that, as in the hen, some internal secretion, acting through the gonad, must 

 inhibit the development of the secondary sexual characters in the hen-feathered cock. 

 Morgan also refers to certain experiments by Goodale who has found that when the hen of 



