202 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
oping from such eggs must be almost invariably female, because males, as 
already stated, are extremely rare. Yet for the very reason that males 
are occasionally produced, we are forced to the conclusion that the male 
character is present, recessive, in the ordinary female of Rhodites. _ If so, 
the egg does not eliminate the character of that sex at the formation of 
the second polar cell, but retains the characters of both sexes, and so has a 
formula, ¢ 9, a supposition for which we have warrant in the mosaic 
gametes of spotted mice. In further support of this idea may be men- 
tioned the observation of Henking, that in the maturation of the egg of 
Rhodites no reduction division occurs ; the nucleus of the ovarian egg, the 
three polar nuclei, and the nucleus of the mature egg, all alike contain 
nine chromosomes each. It is probable, therefore, that normally the 
second maturation division in Rhodites is qualitatively like the first, an 
equation division, in which no segregation of sex characters takes place. 
But the occasional production of a male Rhodites indicates that the 
egg still retains a capacity to eliminate the dominant female character in 
maturation, and so to become male, as do the eggs of other partheno- 
genetic animals under appropriate conditions. 
B. HybDATINA SENTA. 
Hydatina senta differs from other parthenogenetic animals in the fol- 
lowing respects. Its female summer eggs, instead of forming one polar cell, 
form none. Its male summer eges and fecundable (winter) eggs (doubt- 
less at the outset one and the same sort), instead of forming two polar 
cells, form one. It is evident that one of the normal maturation 
divisions has in this species been omitted. Clearly it is not the normal 
second division, for the single one which occurs is a segregation (or 
reduction) division. Manifestly, then, the maturation division which 
is suppressed in Hydatina is the normal first maturation division of 
fecundable eggs, the sole maturation division of eggs not fecundable. 
Corroborative evidence of the correctness of this interpretation comes 
from an unexpected source, the mammals. Sobotta (99) finds that in 
the egg of the mouse there occurs usually only a single maturation 
division. This is the homologue of the second maturation division of 
other animals. When two maturation divisions occur in the same egg, 
the second is always of the same type as the single maturation division of 
other eggs, and it occurs in a like stage of maturity of the Graafian 
follicle. The single maturation division of one type of egg, and the 
second maturation division of the other type, are apparently alike 
reduction divisions, for the mitotic spindle, according to Sobotta’s figures, 
