46 Stet'ile and Hybrid Pheasants 



distinct methods by which an individual can assume secondary sexual 

 characters of the opposite sex, (1) by correlated differentiation, where 

 the abnormality of the gonad induces the developement of characters 

 proper to the other sex, (2) by hereditary transference, where the 

 secondary sexual characters are abnormally distributed in heredity 

 without the gonad being affected at all. 



It is on the basis of these two main subdivisions that a logical 

 classification of secondary sexual characters, both normal and abnormal, 

 should be founded, but it is not the intention in the present paper to 

 apply the principles of this classification any further than to the facts 

 under consideration. It is clear, at any rate, that the four female 

 "mule" pheasants described above are instances of the first phenomenon, 

 viz., correlated differentiation. Three other instances of this process 

 are afforded by the hybrid females, M, B and G, and the sterile pure- 

 bred female, K. The last-named bird, K, was a pure-bred Formosan 

 variety of the Chinese pheasant, P. torquatus, hatched by Mrs H. T. 

 May from stock obtained from Mr W. Trumperant Potts of Correen 

 Castle, Ballinasloe. This bird was hatched in May 1909, and in Sep- 

 tember of that year was observed to " feather up " like a cock, and 

 showed rather more of the red face-skin than a normal female. During 

 this year it also developed a few feathers of the male colour on the 

 inner part of the thigh. In July 1910 it began to tread the hens 

 placed with it and was heard to utter the male cry, though no male 

 plumage appeared until October when a few dark feathers were noticed 

 below the bill. These were lost however at the moult. In 1911 the 

 bird again developed male behaviour and at the September moult 

 began to assume male plumage to a marked degree. During October 

 it acquired a brown-tinted flush over the body, wings and tail, dark 

 feathers appeared on the breast, the white collar characteristic of the 

 male of this species appeared, and the throat and neck feathei-s were of 

 the lustrous green colour found in the male. It was dissected in the 

 summer of 1912, when it showed these characters, and it was found 

 that the ovary was a shrivelled body about six millimetres across, 

 consisting histologically of interstitial and stroma cells with a large 

 invasion of fibrous tissue, but no trace of oocytes at all. The oviduct 

 was in a remarkable condition, being greatly inflamed and hyper- 

 trophied, although the bird had never laid. 



The other three sterile females were all hybrids. M was a hybrid 

 between Reeve's $ and versicolor </. It never laid eggs, and on dis- 

 section during the breeding season at three years old, the ovary was 



