46 CRUSTACEA—BRANCHIOPODA CHAP. 
devoured by the ovarian epithelium, one cell of the remaining 
vroup enlarging to form a winter-egg, fed during its growth not 
only by the three cells of its own set but also by the epithelial 
cells of the ovarian tube, which have devoured the germ-cells of 
other sets. An ovary never contains more than a single winter-_ 
eco at the same time, the number of germ-cells which are 
devoured during its formation varying in the different species; 
the Daphnia drawn in Fig. 15, C, has produced three groups of 
Fic. 16.—Sketch of a parthenogenetic Moina rectirostris, x 45, the brood-pouch being 
emptied and the side of the carapace removed, showing the dome of thickened 
epithelium on the thorax, by which nutrient material is thrown into the brood- 
pouch, and the ridge which fits against the carapace in the natural condition so as 
to close the brood-pouch. 
germ-cells, of which two (II, IIL), will die, while the cell W 
from the remaining group will develop into an ovum; in Moina, 
Weismann finds that as many as a dozen cell-groups may be 
thrown into the ovary before the production of a winter-egg, so 
that only one out of forty-eight germ-cells survives as an ovum. 
The summer-eggs are always carried until they are hatched 
by the parthenogenetic female which produces them. The 
brood-pouch is the space between the dorsal wall of the thorax 
and the carapace. This space is always more or less perfectly 
closed at the sides by the pressure of the carapace against the 
body, and behind by vascular processes from the abdominal 
segments (Figs. 10, 16, etc.). The presence of a large blood-sinus 
