146 GERM-CELL CYCLE IN ANIMALS 



of divisions a number of nuclei which migrate to 

 the periphery, as is the rule in insect development. 

 The " nucleolo" remains during this cleavage period 

 unchanged near the posterior end (Fig. 44, B) ; then, 

 when cell walls appear, it becomes distributed among 



several of the cells 

 thus formed. These 

 multiply less rapidly 

 than the other em- 

 bryonic cells and are 

 the only cells that 

 give rise to the germ 

 cells in the adult. 

 It is thus obvious 

 that there is here an 

 early segregation of 

 germ cells and that 

 these germ cells dif- 

 fer from the somatic 

 cells in the posses- 

 sion of part of the 



((?) at posterior end of an egg. (From disintegrated " nu- 

 Silvestri, 1908.) ^ 



cleolo." 

 The polyembryonic species described by Silvestri 

 are Copidosoma (Litomastix) truncatellus and Agenias- 

 pis {Encyrtus) fuscicollis. The eggs of these species 

 when laid are vase-shaped (Fig. 45), the posterior 

 end corresponding to the base of the vase. Here 

 also a germinal vesicle and "nucleolo" are present, 

 the latter almost always near the posterior end. 

 Parthenogenetic eggs were found to produce males. 



A B O 



Fig. 44. — Oophthora. A. Egg with germ- 

 inal vesicle (A) and "Nucleolo" (N). 



B. Egg containing many cleavage nuclei. 



C. Formation of primordial germ cells 



