GERM CELLS IN THE ARTHROPODA 145 
could find no connection between the polar bodies and 
the cells Petrunkewitsch claims originate from the 
“ Richtungskopulationskern,” but considers these 
“Dotterzellen.” Nachtsheim (1913) agrees with 
Dickel, that these are yolk cells and have no relation 
to the polar bodies. He also finds these cells in both 
fertilized and unfertilized eggs, not as Petrunkewitsch 
states only in the latter. 
The investigations of Silvestri (1906, 1908) on 
parasitic Hymenoptera are of particular interest, 
since in both the polyembryonic species and those 
whose eggs produce a single individual, the keimbahn- 
determinant is considered by him to represent a 
plasmosome which escapes from the germinal vesicle. 
Silvestri (1906, 1908) has described the embryonic 
development of both monembryonic and polyem- 
bryonic hymenopterous parasites. Of the former 
Encyrtus aphidivorus and Oédphthora semblidis were 
studied; in both species the series of events were 
found to be similar. The egg at the time of deposi- 
tion is elongated and irregularly oval in shape (Fig. 
44, A); it contains a germinal vesicle (A) in the 
anterior region and a deeply staining body near the 
posterior end which is called by Silvestri the “ nu- 
cleolo” (N) and is stated to be derived from the 
nucleolus of the odcyte nucleus. The eggs may 
develop parthenogenetically or after fertilization ; 
the unfertilized eggs produce males, whereas the fer- 
tilized eggs develop into females. In either case 
two polar bodies are produced; these disintegrate 
later. The cleavage nucleus produces by a series 
L 
