THE GENERATIVE GLANDS 361 



characteristics are regarded as characteristics of species, then the 

 assumption of a primitive trace, which is equally developed in 

 individuals of both sexes and which undergoes secondary dif- 

 ferentiation through the agency of the genital gland, supplies a 

 more probable hypothesis than that of Tandler, who held that 

 the sexual nature of the secondary characteristics, like that of 

 the genital glands, is determined in the ovum. But even if we 

 accept the first hypothesis, we are compelled to concede that the 

 normal development of the modified characteristics of species is 

 dependent upon the existence of an active genital gland; and 

 that the sexual differentiation of new-born infants is the outcome 

 of the activity of the genital gland during fcetal life. 



We will now proceed to a closer examination of the tw r o 

 conflicting hypotheses concerning the origin of the sexual dimor- 

 phism of the somatic cells. 



The one theory assumes that all the primordial embryonal 

 cells are sexually differentiated, and that the differentiation of 

 the somatic cells takes place before that of the cells of the primi- 

 tive genital trace. The assumption is that the unknown factor, 

 which decides whether the indifferent genital beginning shall 

 develop into a testis or an ovary, also acts upon the somatic cells, 

 thus laying the foundation for those differences of body in the 

 case of the two sexes, which make their appearance at a later 

 developmental stage. 



The evidence in support of this view is supplied by the follow- 

 ing facts : 



In foetuses and new-born infants, a large number of tissues 

 are already sexually differentiated. That female babies have 

 smaller hands and feet and a lower average weight when born 

 than males, is well known. There is also a difference in the 

 brain of the two sexes and there is a very marked differentiation 

 of the bony framework of the pelvis. It is also known that certain 

 anatomical variations occur only in the male, certain others only 

 in the female. According to Rabl and Fischel, supernumerary 

 ribs and vertebrae are more frequently observed in males, while a 

 deficiency in the number of lumbar vertebrse is most frequent in 

 females. 



These observations cannot, however, be regarded as con- 

 clusive ; for differences between the tissues of male and female 

 foetuses do not make their appearance until after differentiation 

 of the genital glands, and the possible influence of the latter can- 

 not be excluded. Fehling was unable to observe female charac- 

 teristics in the pelvis before the fifth month of foetal life, while 

 the primitive genital trace undergoes differentiation in the fifth 

 week. 



The condition of pseudo-hermaphroditism has supplied a 

 large number of facts which point to the independence of the 

 sexual differentiation of the somatic cells from that of the ceils 



