CASTLE : THE HEREDITY OF SEX, 195 



the normal hermaphrodite, probably produces mosaic gametes, ^ 9 , for 

 when in fertilization these unite in pairs, they invariably form hermaph- 

 rodite individuals, ^ 9 • K segregation occurred in the production of 

 the gametes, we should expect the occurrence also of its counterpart, 

 dominance, in fertilization. Since in hermaphrodites the latter does not 

 occur, it is probable that the former does not occur either. 



But in dioecious species sexual dominance almost invariably occurs ; 

 it is probable, therefore, that in such species segregation of sex-char- 

 actex's takes place in the formation of the gametes. If so, and if, as in 

 color heredity among mice, all possible combinations of gametes are 

 formed in fertilization, and in the frequencies demanded by the law of 

 chance, the sex of the oflfspring should be indicated by the product, — 



(? + 9 (ova) 



(? + 9 (spermatozoa) 



SS + -2^9 + 99 (zygotes). 



According to this, half the offspring, it will be observed, must be pxirely 

 of one sex or the other ; that is, must contain and transmit the characters ■ 

 of one sex only. But we have no reason to think that such sexually 

 "pure" individuals exist. On the contrary, when, as in the case of the 

 honey-bee, the individual apparently transmits uniformly the character 

 of one sex, that sex is invariably the opposite to its own. It is highly 

 probable, therefore, that an egg bearing the character of one sex can 

 unite in fertilization only with a spermatozoon bearing the character of 

 the opposite sex. Our present knowledge of the process of fertilization 

 indicates that in it a union is accomplished between elements strictly 

 equivalent to those which were separated in the formation of the 

 gametes. But there exist, as we have'seen, strong reasons for believing 

 tliat in the formation of the gametes, opposite sex-characters are sepa- 

 rated. Consequently, on a prio7-i grounds, we should expect only 

 opposite sex-characters to unite in fertilization. 



But, some one may object, if a ripe egg of one sex can be fertilized 

 only by a spermatozoon of the opposite sex, it follows that half the eggs 

 produced are infertile toward half the spermatozoa. This, however, is 

 not so serious an objection as it may at first thought seem to be. It 

 does not involve impotency of half the eggs and spermatozoa, nor of any 

 portion of them. All the eggs of one sex will be fertile toward all the 

 spermatozoa of the opposite sex ; the remaining eggs will be fertile 

 toward the remaining spermatozoa. The infertility which exists is only 



