80 THE GENETIC AND THE OPERATIVE EVIDENCE 



The influence of the ovary in suppressing the cock plumage has been 

 convincingly shown in an experiment of Goodale's, in which, after 

 removal of both testes from the young Leghorn cock, pieces of ovaries 

 were inserted into the body-cavity. As dissection showed later, several 

 of these implanted pieces grew onto the wall of the body-cavity. The 

 birds developed the plumage of a hen, although some traces of the male 

 plumage were at times present. The difference between the sexes is so 

 great in Brown Leghorns that the hen-feathering of the feminized 

 cockerels leaves no doubt that the presence of the ovary had produced 

 the female coloration. 



Geoffrey Smith and Mrs. Haig Thomas (1913) have examined a 

 number of hybrid pheasants, some of which were sterile. They found 

 that the ovary (and oviduct) was often small and degenerate. There 

 was a more or less corresponding tendency for such female hybrids to 

 show male feathering, at least in a part of the plumage. The degenera- 

 tion of the sex element, however, does not take place until after the 

 time of synapsis, so that the younger germ-cells may be normal. The 

 later degeneration of these cells is not likely to influence the secondary 

 sexual characters, but may be an index of changes in other parts of 

 the ovary. 



Geoffrey Smith had a breed of White Leghorns with cocks of two 

 classes — those that assumed cock plumage at 6 months, and those that 

 are like the hens for 8 months, after which they slowly assume the 

 cock-feathering. The difference is hereditary and appears to segregate. 

 Possibly this breed had one factor at least for hen-feathering that is 

 more effective for young birds than for older ones. 



Smith states that birds and crabs (see infra) appear to give opposite 

 results, since removal of the ovary in the former leads to development 

 of secondary male characters and removal of testes in the latter to 

 secondary female characters. But he adds that he thinks the results 

 are really the same, because in the crab it is not the suppression of the 

 testis but the feminization of the male by the Sacculina that causes the 

 change. 



There are a number of observations on ducks. Several cases have 

 been recorded where in old age the female assumed the male plumage 

 (Darwin, Shattock, and Sellheim). Also a few cases in which the testes 

 were removed. Those of Goodale are the most complete and striking. 

 The male duck has two characteristic plumages, one called the nuptial 

 also called the summer or breeding plumage that is assumed at 

 the molt in the autumn, and the other the eclipse plumage, which is 

 not identical with but much like that of the female. Here, then, we 

 find a new situation, and one that invites comparison with the con- 

 dition in Sebrights, in so far as the male becomes hen-feathered at 

 certain seasons. 



