THE LIVING BIRD 43 



be quite simply verified by castration, i.e. by surgical 

 removal of the testes. Provided the operation is 

 successful and complete, he never again exhibits 

 these characteristic male traits. He is permanently 

 sexless. In similar manner, after removal of the 

 ovary {ovariectomy) a female bird will drop its 

 normal female behaviour and (in poultry) will don 

 plumage resembling that of the male. When this 

 operation is performed, it frequently happens that 

 the ovary of the right side, hitherto vestigial, begins 

 to develope, but it frequently developes, not as an 

 ovary, but as a testis. The bird now comes under 

 the influence of testicular hormones. Theoretically 

 it should begin to exhibit male behaviour and this is 

 actually the case. The bird at its next moult 

 assumes male plumage, developes the head furnish- 

 ings of the male (in poultry), crows, and may actu- 

 ally attempt to mate with other hens. In one 

 extreme case such a sexually reversed bird, a good 

 egg producer till three years old and the mother of 

 chickens, began to crow at 3 J, took on all the male 

 characters (except that she retained her female 

 stance) and at 4J, on being mated to a virgin hen, 

 became the father of two chicks. 



In gonadectomized birds, originally of either sex, 

 male sexual behaviour can be called forth either by 

 grafting another testis in some part of the body, or 



