CASTLE: THE HEREDITY OF SEX. 215 
11. Possibly the testis, in males of parthenogenetic species, contains 
the male character as well as the female. If so, these are doubtless 
segregated in spermatogenesis, but only the female spermatozoa can be 
functional, because only male fecundable eggs are produced by such 
species. 
12. The segregation of sex-characters takes place in most partheno- 
genetic animals, and doubtless in dioecious animals also, at the second 
maturation division (the “ reduction division”) of the egg, and probably 
at a corresponding stage in spermatogenesis. For (1) eggs which de- 
velop without fertilization and without undergoing a second maturation 
division contain both the male and the female characters, the former 
recessive, the latter dominant; but (2) in normally parthenogenetic 
species, eggs which, after undergoing a second maturation division, 
develop without fertilization, are always male (except in Rhodites). In 
such species the female character regularly passes into the second polar 
cell, the male character remaining in the egg. In dioecious animals, 
on the other hand, eether sex character may remain in the egg after 
maturation. 
13. In Hydatina senta there is no maturation division homologous 
with the first maturation division of the eggs of other animals. A single 
maturation division occurs in the male (or fecundable) eggs, but this is 
clearly homologous with the second maturation division of other parthe- 
nogenetic animals, for in it a segregation of sex-characters takes place. 
In the female parthenogenetic egg, no maturation division occurs. 
14. The parthenogenetic egg of Rhodites rosae undergoes two matura- 
tion divisions, but apparently without the occurrence of segregation in 
either of them. If segregation does occur in one of the two maturation 
divisions, the character retained in the egg must be regularly the female, 
because the offspring are uniformly of that sex. In that case, the geni- 
tal gland of Rhodites probably develops, as does the testis of the honey- 
bee according to Petrunkewitsch, from the fused polar cells. 
15, Abnormal sex-proportions among hybrids are capable of explana- 
tion, in some cases, on the ground that certain combinations of gametes 
are infertile. 
16. Sexual dimorphism, in a species, is the result of coupling, in 
the zygote and in the gametes, of certain form-characters with one or the 
other sex-character. <A similar explanation accounts satisfactorily for 
abnormal sex-distribution of the offspring, in the case of certain crosses, 
between the two parent forms. . 
