SEXUAL CHARACTERS OF SOME DOMESTIC BIRDS. 51 



RELATION BETWEEN THE GONADS AND THE SECONDARY SEXUAL 

 CHARACTERS IN OTHER GROUPS. 



The influence exerted by the gonads on the secondary sexual char- 

 acters varies from group to group. In insects, the secondary sexual 

 characters are independent of the gonads. In certain crustaceans 

 conditions are the reverse of those found in birds. In mammals, 

 removal of the testes produces an effect very similar to that on the male 

 bird . The female, however, undergoes very httle change in her secondary 

 sexual characters. Steinach, however, has shown that by transplanting 

 ovaries into the castrated male — rat or guinea-pig — he becomes femin- 

 ized. Bresca found in Triton that the crest of the tail did not develop 

 after castration, while Nussbaum found for the frog that the thumb pads 

 failed to develop, though Smith secured results opposed to Nussbaum's. 



On the whole, the relation between the gonads and the secondary 

 sexual characters appears to be specific and not general. Although 

 more striking, their relation is essentially of the same order as other 

 morphogenetic secretions, such as that of the thyroid. Indeed, the 

 morphogenetic activity of the gonads is by no means confined to the 

 secondary sexual characters, but produces other well-known effects. 



SUMMARY. 



1. If the ovary of a domestic bird be removed completely, many of 

 the secondary sexual characters of the male appear. Some individuals 

 become nearly complete replicas of the male, others imperfect imita- 

 tions of the male. 



2. If the testes be removed, the majority of the secondary sexual 

 characters of the male develop, though a few may remain in an infantile 

 condition. 



3. Castrated drakes lose the power of developing the summer 

 plumage. 



