SEXUAL HORMONES AND MORPHOGENESIS 471 



but yet do not belong to the first group in our genetic system. 

 Zawadowsky refers here to the sex characters of insects, and 

 perhaps some characters in birds which are present in the male 

 but do not appear in the castrated female, such as possibly the 

 spurs and the red ring around the eye of the male pheasant. 



When we consider what we learned about the dependence of 

 the sex characters upon the sex glands it becomes clear that the 

 classification into primary and secondary sex characters must 

 be abolished as causing endless misunderstanding, since the 

 term secondary often implies genetic dependence. Whether 

 any sex character is genetically dependent upon the sex gland 

 can be shown only by thorough analysis, as in the case of the 

 plumage in birds. Further, the term " sex gland" may include 

 diverse tissues, and the question is still open as to which 

 part of the sex gland is involved in internal secretion and to 

 what extent. All parts of the sex gland are not to be considered 

 as genetically primary sex characters, ripe spermatozoa and 

 ripe ova not being necessary for the performance of the endo- 

 crine function of the gonad. Though different phases in the 

 development of the generative cells may be involved in the 

 processes of internal secretion (see "follicular theory," p. 176), 

 the generative cells, as we have seen, may be influenced by 

 hormones produced by the sex gland, i.e., the generative cells 

 may become genetically dependent upon sex specific hormones. 

 In view of these considerations it seems inadvisable to pre- 

 serve a classification which is capable of giving rise to so 

 much misunderstanding. 



For practical use we need a system similar to the old classifi- 

 cation into primary and secondary sex characters, but such as 

 at the same time will not cause the old confusion. 



Poll (1909, p. 347) was the first to make a step in this 

 direction. He classified the sex characters in the following way : — 



Differentiae Sexuales: 

 I. Essentiales s. germinales 

 2 Accidentales. 



(a) Genitales subsidiariae. 

 Internae. 

 Externae. 

 (h) Extragenitales. 

 Internae. 

 Externae. 



