SEX AND SEXUAL CHARACTERS 469 



like the beard, develop only at puberty; and the same is true 

 of haemophilia, which shows itself even in infancy. It seems 

 evident then that there are two kinds of sexually-limited 

 characters : those which develop only at sexual maturity, and 

 are affected by castration, and (on the other hand) those which 

 are confined to one sex, but are independent of the presence and 

 functional activity of the gonads. The sexual dimorphism due 

 to the second kind may be explained on Mendelian principles, 

 and its origin may be that which is assumed by Mendelians for 

 all characters — that is to say, such sex-limited characters may 

 arise as mutations which (for reasons yet unknown) are coupled 

 with the primary sex-characters. The other kind of sexual 

 dimorphism cannot be explained on Mendelian principles, and 

 the special relation of the characters to which it is due to the 

 functional activity of the gonads can only be explained on the 

 hypothesis that these characters are of somatic origin. 1 



Bateson's theory of sex appears to have been originally pro- 

 posed in order to account for the heredity of the character of 

 the lacticolor variety of Abraxas grossulariata. The fact that in 

 nature this variety occurs only in the female sex indicates that 

 the colour-character is connected with that sex ; but it is scarcely 

 a secondary sexual character, because in artificial breeding 

 experiments male lacticolor were produced. Bateson's theory 

 is not the only one on which the peculiar facts of this case can 

 be explained ; for Doncaster himself previously explained them 

 by another, which seems more complicated, but is less open to 

 objection, in my opinion, than Bateson's. In Doncaster's theory 

 there are four assumptions : 



(1) Each sex gives off male-bearing and female -bearing 

 gametes in equal numbers. 



(2) In heterozygous females lacticolor is coupled with the 

 female character and grossulariata with the male, but in hete- 

 rozygous males there is no coupling. 



1 Another distinguishing characteristic of secondary sex-characters which are 

 dependent on the sexual hormones is that in the course of evolution they tend to 

 emancipate themselves from this restriction, and then develop equally in both 

 sexes. Examples of this change are afforded by the reindeer and by numbers of 

 ruminants in which the horns are developed in both sexes, and also by many breeds 

 of domesticated fowls in which the comb and wattles of the hens are no longer 

 rudimentary, as in the original species ; in some even the spurs are beginning to 

 appear in the hens. This shows that there is no close connection or coupling of 

 the character with the primary sex-character in the gamete. 



