SEX AND SEXUAL CHARACTERS 465 



In the lower Vertebrates there is direct evidence that the 

 primary female character is present in the males. Years ago 

 I showed (4) that in Myxine the gonad is hermaphrodite. 

 Schreiner (5) has recently maintained that even here the male and 

 female elements do not come to maturity in the same individual ; 

 but there is not the slightest doubt that ova are present in large 

 numbers in the functional males. It has also been shown that 

 ova occur frequently in the testes of Petromyzon, many Teleosts, 

 and many Amphibia. In toads an organ attached to the anterior 

 end of the testes, and known as Bidder's organ, is present in all 

 males, and contains ova which do not come to maturity. It 

 sometimes contains spermatozoa also, and it occurs also in 

 females : but here we are considering only the evidence of the 

 presence of ova in males. Perhaps it will be suggested that 

 there is no evidence of this kind with regard to reptiles, birds, 

 and mammals, and that in these the female sex is absent in the 

 males. It is true that the gonads seem more completely 

 differentiated in these higher Vertebrates ; but this applies to 

 males and females equally — so that we ought to conclude that 

 both sexes are sexually pure. But it is at least possible that 

 even in the higher classes of Vertebrates each gonad contains 

 reproductive cells of the opposite sex. In both ovary and testis 

 there are peculiar cells, known as the " interstitial cells," which 

 resemble epithelial cells, and differ from the elements of the 

 stroma. According to the researches of Miss Lane Claypon, these 

 interstitial cells are derived from the germinal epithelium, and 

 are therefore reproductive cells, or gametes which never come to 

 maturity ; and it is possible that they represent the gametes of 

 the opposite sex — a rudimentary ovary in the male, a rudi- 

 mentary testis in the female. The condition of the lower 

 Vertebrates suggests that these, and perhaps all animals — like 

 plants — were originally hermaphrodite, and that the differentia- 

 tion of sex was evolved by the reduction of one set of gametes 

 to the rudimentary condition. 



Where the evidence is obviously opposed to the conclusion 

 that the males are homozygous in sex, Bateson and Doncaster 

 suggest that the female is homozygous and the male hetero- 

 zygous, the conditions being different in different animals. 

 They accept the conclusion of Geoffrey Smith, from his observa- 

 tions on Sacculina, that the effect of parasitic castration on the 

 male crab is the assumption of the characters of the female, 



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