castle: the heredity of sex. 193 



not occur at the formation of its gametes. Nevertheless a mosaic indi- 

 vidual does occasionally occur which produces a certain proportion of 

 segregated (that is, pure) gametes. Exceptionall}' a spotted mouse 

 when paired with a recessive mate produces pure recessive (white) 

 offspring as well as hybrid (dark) offspring. The peculiarity is inherent 

 in the parent and is manifested with uniformity by certain individuals, 

 but not at all by others. 



IV. Application of the Principles Stated. 



1. Dioecious and Hermaphrodite Organisms. 



Sex in dioecious animals and plants is inherited in accordance with 

 Mendel's law; that is, in accordance with the principles of dominance 

 and segregation. The ordinary dioecious individual is a sex-hybrid or 

 " heterozygote " (Bateson), in which the characters of both sexes are 

 present, one dominant, the other recessive. In the male, the female 

 character is recessive, and conversely in the female, the male character ; 

 but each sex transmits the characters of both. 



The existence of each sex (in a latent condition) in the other is 

 shown by the occurrence in each sex of rudimentar}^ organs peculiar 

 to the other. This evidence is supported by numerous observations 

 brought forward by Darwin ('76) to show that an animal in its old age, 

 or when its genital organs become diseased, often manifests characters of 

 plumage or of voice, or even instincts, which are characteristic of the 

 opposite sex. 



But perhaps the strongest evidence of the latency of each sex in the 

 other is afforded by the transmission through one sex of the characters 

 of the other. Thus, as Darwin states, when the domestic cock is crossed 

 with the hen pheasant, the male offspring have the secondary sexual 

 characters of the viale pheasant ; these, manifestly, must have been 

 inherited through the female pheasant. 



Again, in many animals which reproduce by parthenogenesis, the 

 female bears (without fertilization) both male and female offspring, 

 showing that she really possesses both sex-characters. 



Experimental evidence of the latency of one sex in the other in plants 

 has been produced by Bordage ('98). He cut back the apex of young 

 male plants of Carica papaya, just before the appearance of the first 

 male flowers. Lateral branches, two on each plant, then arose immedi- 

 ately below the cut, and these produced female flowers and fruit. 



