RESULTS ^OF^ CASTRATION 7 1 



(b) It is probable that the somatic basis of mammals and 

 birds is sexually undifferentiated, i.e., it is asexual or bisexual 

 at the beginning, being changed during embryonic Hfe in the 

 male or female direction by the differentiating sexual gland. 

 In other words, we suggest that those sexual differences which 

 develop under the action of the sexual glands are really caused 

 by this action only. On the contrary, those sexual differences 

 which develop and exist independently of a formative or preserv- 

 ing action on the part of the sexual glands might be explained 

 as the result of the independent development of asexual charac- 

 ters common at the beginning to both sexes. These characters 

 merely become sexual owing to their being changed in one of the 

 sexes by the sexual glands, as, for instance, the bright plumage 

 and the spurs in the cock on the one hand, and the dull plumage, 

 and the lack of spurs in the hen on the other. The sexual 

 characters which are independent of the sexual glands must 

 not be mistaken for those which are only apparently inde- 

 pendent and which remain after castration, merely because 

 the formative action of the sexual glands has already taken 

 place and because the duration of this action was long enough 

 to fix these sexual characters in the asexual embryonic soma. 



The first three theses and the first part of the fourth are really 

 statements of ascertained facts on which it is only possible to 

 raise doubt in regard to details, whereas the second part of the 

 fourth thesis is a matter of hypothesis. It will be our purpose 

 in the latter part of this book to present further evidence in 

 support of this hypothesis. 



BIBLIOGRAPHY FOR CHAPTER 11, 



[* Not seen in the original.] 



Amantea. 1919. Sulla secrezione spermatica. VIII. Alcune os- 

 servazioni su cani castrati e su cani sottoposti a escissione 

 parziale dei deferenti. Atti della B. Acad, dei Linceif 28, 

 ser. 6a. 



Aron. 1921a. Sur le conditionnement des caracteres sexuels second- 

 aires chez les Batraciens Urodeles. C. R. de VAcad. d. Sc, 

 173, p. 482. 



— - 1921b. Sur r existence et le r61e d'un tissu endocrinien dans le 

 testicule des Urodeles. G. B. de VAcad. d. Sc.y 173, p. 57. 



