94 THE GENETIC AND THE OPERATIVE EVIDENCE 



connection, but as I have recently reviewed these results in the paper 

 on gynandromorphs written in collaboration with C. B. Bridges,^ I 

 need only refer to that account here. 



[Note added April 21, 1919.] 



Shortly after the preceding paper was finished a theses by A. P^zard on the 

 secondary sexual characters of birds reached me. In it the author gives an 

 account of a number of experiments that he has made with poultry and with 

 pheasants. His description of the changes that take place after castration 

 are more exact and more detailed than any other so far recorded; but in general 

 the results obtained by P^zard, through castration, are the same as those 

 that had been obtained by others. Castration of 4 male silver pheasants are 

 reported. No change in the plumage results, although the changes that take 

 place in the comb and wattles are the same in kind as those observed in fowls. 

 The sexual instincts and peculiarities of the voice and their belligerency are also 

 lost. Sunilarly 4 golden pheasants that were operated on gave the same results. 



Three pheasants with mixed plumage {Phasianus colchicus) were examined. 

 Their testes proved, on histological examination, to be imperfectly developed. 

 It is not evident what relation existed between the facts and the mixed plmn- 

 age. The suggestions made by P6zard seem inadequate to cover the cases. 



Testicular tissue transplanted into castrated cocks whose comb, wattles, 

 etc., had undergone retrogressive changes brought about a return to the normal 

 conditions after an interval during which the implanted nodules had begun 

 to regenerate. 



Testicular extract from the cryptorchid testes of swine was injected into 

 castrated cocks. In one case this resulted in a rapid growth in size of the 

 comb, which, after 2 months, had reached its full size. Cessation of the injec- 

 tions led immediately to a cessation of growth. Before injection the bird 

 exhibited the pacifistic characteristics of the capon, but the injections brought 

 out httle by httle the aggressive behavior of the normal male. The voice 

 reappeared and "nous assistons k une veritable crise de puberte." 



A histological study of the testes of the fowl and of pheasants showed that 

 much connective tissue is characteristic of young birds. In the adult cock, 

 and during the mating season of the pheasant, the connective tissue becomes 

 largely crowded out by the enlargement of the tubules. P^zard concludes 

 that the "interstitial" cells in birds have nothing to do with the secondary 

 sexual characters, but that these come rather under the influence of the ger- 

 minal cycle of cells of the testes. The submergence of the connective-tissue 

 cells of pheasants during the breeding-season and their reappearance during 

 the rest of the year might appear to have some relation to the facts that I 

 have recently described in Sebrights, but as the nuptial plumage of the male 

 remains the same throughout the year we can not ascribe any direct influence 

 to this tissue. Nevertheless, the different tissues of the testes in birds that 

 show seasonal dimorphism of plumage should be carefully examined. 



P^zard made a few observations on hens whose ovary had been removed. 

 His results are in accord with those of Goodale, except that he thinks that the 

 ovary has no influence on the erectile organs (comb, etc.) which acquire in the 

 spayed bird the same lengA as that of the normal female. 



Two hens showing male characteristics and a pheasant similarly affected 

 are described. In all three cases an examination of the ovary was foimd to 

 be imdeveloped or abnormal. 



' Carnegie Inst. Wash. Pub. No. 278, 1918. 



