148 GERM-CELL CYCLE IN ANIMALS 
whereas fertilized eggs give rise to females. First 
and second polar bodies are formed and the first 
divides, thus making three in all. The events of 
early cleavage are the same whether the nucleus 
consists of the female pronucleus only or of the 
female and male pronuclei fused. Unlike the eggs 
of monembryonic species, the cleavage nuclei here be- 
come separated from one another by cell walls and 
the “ nucleolo” from the very beginning is segregated 
at each division in a single cleavage cell (Fig. 45, D). 
This cell divides more slowly than the others; the 
“nucleolo” gradually becomes vacuolated, breaks 
down, and finally is evenly scattered throughout 
the entire cytoplasm. Just before the sixteen-cell 
stage is reached the cell containing the disintegrated 
“nucleolo” divides and the two daughter cells are 
provided with equal amounts of its substance (Fig. 
45, F). Silvestri was only able to trace the cells 
containing the remains of the “nucleolo” until 
four of these were present. Nevertheless, he con- 
cludes that these and these alone give rise to the 
germ cells. This conclusion seems well founded when 
the history of this ‘“nucleolo” is compared with 
that of similar bodies (keimbahn-determinants) 
in the eggs of certain other animals. 
Two regions develop in the eggs of these polyem- 
bryonic HyMENopTERA: (1) an anterior or polar re- 
gion containing the polar bodies, and (2) the posterior 
embryonicregion. The latter again becomes differen- 
tiated into two regions: (1) an anterior “‘massa germi- 
nigera,”’ which gives rise to normal larve, and (2) a 
