164 Crossing the North and South African Ostrich 



The secondary sexual colours of the skin and plumage of the ostrich 

 are thus determined by altogether different influences ; the full attain- 

 ment of the one is dependent upon the presence of the testes and of the 

 other upon the absence of the ovaries. Two North African birds at 

 Grootfontein, although about six years old, have shown no signs of 

 sexual maturity ; they retain the cream yellow of all northern young 

 birds and mature hens, but have the black plumage of cocks. Evidently 

 some abnormality is connected with the internal gonads, but from the 

 external appearance of the birds it is impossible to say whether they 

 are cocks or hens. It may be noted that the removal of the ovaries or 

 testes, especially after a bird has attained maturity, has little or no 

 effect on certain of the sexual instincts. Thus a castrated hen will go 

 through the characteristic snapping of the beak and fluttering of the 

 wings as if broody, and will even crouch to receive the cock ; while the 

 castrated cock will perform his ordinary "rolling" display and even 

 mount a crouching hen. 



In determining the sexual colours of the male ostrich the testes 

 clearly give rise to some secretion, presumably of an enzyme nature. 

 This must be produced at first in small quantities, and the colour changes 

 come slowly ; but as the testes ripen and become functional more of the 

 enzyme must be forthcoming, for the colour intensity increases and 

 remains brilliant throughout the mating period. With the beginning 

 of the six weeks' period of incubation the testes become less active, 

 pairing ceases, less enzyme is produced and the colour fades. The 

 differences between the sexual colours of the northern and southern bird 

 are well defined, and must be germinal in the first instance; but the 

 factors must act through the gonads, and presumably these exert their 

 influence by means of specific enzymes. Even if we regard the germinal 

 factors as themselves enzymes, as Troland ^ and others would have us do, 

 those concerned with the sexual colours must express themselves through 

 the gonads. 



Though the scarlet colour of the cock is a secondary sexual character 

 it may well be doubted whether it has any influence on the mating of 

 the birds, or any preferential value in the eyes of the hen, as is so often 



ordinary breeds of fowls is spayed she develops the full male plumage, as is also proved 

 above for the hen ostrich. Seeing that the plumage of the cock ostrich is more valuable 

 than that of the hen the results from spaying the latter have an economic bearing and the 

 practice is followed by some farmers. 



1 Troland, L. T., "Biological Enigmas and the Theory of Enzyme Action," Amer. 

 Nat. Vol. LI. June, 1917. 



