34 



ON THE ORIGIN AND 



[CHAP. 



having collected some of the transparent eggs of 

 a small Beetle (Rhynchites betitleti], to his great 

 surprise found more than half of them attacked by 

 a parasite, which proved to be the larva of a minute 

 Hymenopterous in-sect belonging to the Pteromalidae. 

 Fig. 15 shows the egg of the Beetle, with the parasitic 



"A 



FIG. 14. Larva of Sirex (Westwood, loc. cit.) 15, Egg of Rhynchites, showing the 

 parasitic Larva in the interior. 16, the parasitic Larva more magnified. 



larva, which is represented on a larger scale in 

 Fig. 1 6. 



More recently this group has been studied by M. 

 Ganin, 1 who thus describes the development of Platy- 

 gaster. The egg, as in allied Hymenopterous families, 

 for instance in Cynips, is elongated and club-shaped 

 (Fig. 17). After a while a large nucleated cell ap- 

 pears in the centre (Fig. 18). This nucleated cell 

 divides (Fig. 19) and subdivides. The outermost cells 

 continue the same process, thus forming an outer 

 investing layer. The central, on the contrary, en- 

 larges considerably, and develops within itself a 

 number of daughter cells (Figs, 20 and 21), which 

 gradually form a mulberry-like mass, thus giving 

 rise to the embryo (Fig. 22). 



1 Zeits. fur Wiss. Zool. 1869. 



