castle: the heredity of sex. 197 



for example, produce both male and female offspring from unfertilized 

 eggs! (2) The eggs of Dinophilus, laid by the same mother, are 

 of two distinct sizes, one about three times as large as the other. 

 From the larger sort develop females, from the smaller, males (see 

 Korschelt, '87). (3) Similar morphological differences, though less 

 obvious ones, exist between the male and female eggs of the gypsy-moth, 

 Ocneria dispar, according to Joseph ('7l) and Cuenot ('99), and of 

 the silk-moth, Bombyx mori, according to Brocadello as quoted by 

 Cuenot. This case is supported by the observations of von Siebold 

 ('56) and others, which show that eggs of the two species mentioned 

 occasionally develop ivithout fertilization, and that in such cases normal 

 individuals of hotli sexes are produced. 



On the other hand, dimorphic spermatozoa exist in the case of 

 Paludina and some other animals, bat there is no adequate reason at 

 present for supposing that this dimorphism is related to sex. The 

 consensus of opinion on the part of those who have studied these cases 

 is that the more usual form of spermatozoon alone is functional, the 

 other being pathological. Nevertheless, the subject is one meriting 

 further investigation. 



The occasional occurrence of cases of true hermaphroditism, in species 

 normally dioecious, may be cited as evidence in favor of the hypothesis 

 of sex presented in this paper. Each dioecious individual, we have sup- 

 posed, is a potential hermaphrodite, but has tlie characters of one sex re- 

 cessive. The true hermaphrodite (I'are in dioecious species) is an animal 

 in which neither sex is recessive, but the characters of both sexes are devel- 

 oped together. Unilateral and mixed hermaphrodites are an exceptional 

 form of sex-mosaic : they may in some cases be animals in whose devel- 

 opment fusion of the pronuclei has not occurred, one side or region of 

 the body containing only nuclei derived from the male, the other from 

 the female gamete. A similar result might follow, if, even after fusion 

 of the pronuclei in the egg, segregation of sex-characters should occur in 

 cleavage, instead of the normal equation divisions. Or, thirdly, a mosaic 

 sex-character may exceptionally be possessed by the gametes themselves, 

 comparable with the mosaic character as to color possessed by the 

 gametes of spotted mice. 



Gynandromorphic individuals, not rare among arthropods, clearly 

 result from imperfect dominance of the characters of one sex over those 

 of the other. It is significant that such individuals are especially com- 

 mon among hybrids, which represent abnormal combinations of gametes 

 untried and uncertain as to their relative strength. One of the most 



