642 



CLASS IV. INSECTA. 



larvae of moths of the genus Hyponomeuta, and it is in an egg of 

 the latter that the Encyrtus deposits its own egg. By a remark- 

 able process of nuclear fission a single egg of this parasite gives 

 rise to over a hundred embryos, arranged in the form of a con- 

 tinuous chain, and lying in the body cavity of the larval host. 

 The resulting larvae devour the organs of their host and pass 

 into pupae under its now empty skin, and after a short interval 

 the winged Chalcids emerge. 



Silvestri has studied another member of this family viz. 

 Litomastix truncatellus, which is similarly parasitic in the eggs 



FIG. 402. The formation of the blastoderm in Uydropltilus (after Heider). 6 developed 

 blastoderm; d food-yolk; / so-called cleavage-cells; k peripheral protoplasm; z yolk- 

 cells. 



of the Noctuid moth Plusia gamma. In this case it was dis- 

 covered that a single Litomastix egg produced about a thousand 

 "sexual" larvae and a hundred or more "asexual' larvae 

 within its host. The former alone are transformed into adults, 

 the latter subsequently perish. 



In the family Proctotrypidae Marchal has studied a species, 

 Polygnotus minutus, which is parasitic in the larva of the 

 " Hessian ' : fly (Cecidomyia destructor). In this instance the 

 embryos resulting from the fission of a single egg seldom reach 

 twelve in number. 



In both families it has been ascertained that the winged 

 parasites which emerge from a single host most often belong 



