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 Oophthora 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" (A 7 ") and is stated to be derived from the 

 nucleolus of the oocyte 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 



