EFFECTS OF GONAD GRAFTS IN CHICKS 3 



here. With reference to birds, it may merely be said that 

 Goodale ('16) and Pezard ('18) have demonstrated in the most 

 convincing manner that certain secondary sexual characters of 

 domestic birds are dependent on the secretions of the gonads. 



Varying degrees of reversal of certain sex characters have been 

 observed or experimentally obtained in both vertebrates and 

 invertebrates by several investigators. Thus Steinach ('12, '13) 

 described a reversal of several sex characters in the guinea-pig 

 and rat produced by transplanting the gonads of the opposite 

 sex into castrated or spayed individuals. His statements have 

 been partially verified by Moore ('19). These experiments show 

 that in these mammals certain sexual characters, both somatic 

 and psychic, are controlled by the internal secretions of the 

 gonads. Riddle ('16) found that in certain crosses between 

 pigeons intersexual forms arose in correlation with a certain 

 phase of the breeding cycle. Pearl and Boring ('18) investigated 

 several hermaphroditic fowls and found that they possessed 

 pathological gonads, which were probably responsible for the 

 hermaphroditic condition. Bond ('14) reported an interesting 

 case of a hermaphroditic pheasant of the Formosan variety which 

 displayed male secondary characters on the left side of its body 

 and female characters on the right side. The bird possessed a 

 single gonad, the left one, and this was in part testicular, in part 

 ovarian. Bond believed hormones secreted by the hermaphro- 

 ditic gonad were responsible for the external hermaphroditism. 



Among invertebrates the studies of Baltzer, Goldschmidt, and 

 Gould are of great interest. Baltzer ('14) found that in the 

 Gephyrean worm Bonellia, the indifferent larva becomes a male 

 only when it attaches itself to a female; otherwise it develops 

 into a female. A closely similar case was described by Gould 

 ('17, '19) for Crepidula. In this protandric gasteropod, male- 

 ness develops only when small individuals come in contact with 

 or remain within a short distance of a large female or transitional 

 form. Gould was convinced by his experiments that the devel- 

 opment of male characters is directly due to the effect on sexually 

 indifferent individuals of a certain substance produced by large 

 animals. Baltzer and Gould did not claim that the substances 



