DETERMINATION OF SEX. 903 



that the determination of sex resides in the maternal organism alone. 

 Some of the facts that support this view with more or less con- 

 clusiveness are as follows: (1) In certain worms (Dinophilus) eggs 

 of two sizes are produced; the large eggs on fertilization develop 

 always into females, the small ones into males. Similar facts are 

 recorded for other animals (Hydatina). (2) Many species of in- 

 vertebrates exhibit the phenomenon of parthenogenesis, that is, 

 the eggs of the mother develop without fertilization. In some 

 cases this method forms the only means of reproduction, and the 

 individuals of the race are all females. But in other animals re- 

 production is effected either by parthenogenesis or by fertilization 

 according to the conditions, change of seasons, etc. Among 

 these latter animals it may be shown, in some cases at least, that 

 the parthenogenetic eggs may give rise either to males or females, 

 a fact which accords with the hypothesis of the existence of male 

 and female eggs in the mother. (3) In man twins may be born. 

 These twins may be of two kinds. First, those that are developed 

 from two different eggs, each of which has its own chorion and 

 develops its own placenta. This kind may be designated as false 

 twins, and in the matter of sex they may be male and female, 

 or both male, or both female. The matter varies as in the statis- 

 tics of births in general. In the other group, however, of true 

 twins or identical twins, the two embryos are developed from a 

 single ovum and are included in a single chorion. In such cases 

 the sexes of the twins are always the same, they are both boys 

 or both girls. This fact favors the view that the sex may be pre- 

 determined in the ovum, which may be either male or female. 

 However, if we grant the fundamental fact, so far as the ova are 

 concerned, that they are either male or female at the time of forma- 

 tion or are made so during the process of growth and maturation, 

 it is still logically possible that there may also be male and female 

 spermatozoa, and that in the union of the two cells the sex of the 

 fertilized ovum may be referable either to the ovum or spermatozoon. 

 It is not justifiable to assert that the paternal organism is without 

 influence upon the sex of the offspring. In fact, in the case of 

 honey bees it is observed that if the egg of the queen bee is unfer- 

 tilized it develops into a male, but, if fertilized, into a female, thus 

 indicating a determining influence upon the part of the male ele- 

 ment. Moreover, Wilson * has obtained some interesting results 

 upon insects (hemiptera) which indicate that the determination of 

 sex in these animals is dependent upon or correlated with a visible 

 difference in the chromosomes of the spermatozoon. In some cases 

 one-half of the spermatozoa contain an unpaired or accessory 

 chromosome. Those showing this structure produce females on 

 * Wilson, "The Journal of Experimental Zoology," 1906, iii., 1. 



