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 (71) and Cuénot (’99), and of 
the silk-moth, Bombyx mori, according to Brocadello as quoted by 
Cuénot. This case is supported by the observations of von Siebold 
(56) and others, which show that eggs of the two species mentioned 
occasionally develop without fertilization, and that in such cases normal 
individuals of both sexes are produced. 
On the other hand, dimorphic spermatozoa exist in the case of 
Paludina and some other animals, but 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 spermatozodn 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 the characters of one sex re- 
cessive. The true hermaphrodite (rare in dioecious species) is an animal 
in which nezther 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 ouly 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 
