DEVELOPMENT OF THICHOGRAMMA EVANESOENS. 157 
were a spermatozoon, though in some insects no clearing of 
the cytoplasm around the male pronucleus, or other event, 
takes place at this period. In the stage later, during the 
formation of the polar bodies, the granules which were 
present in PL 11, fig. 10, around the male pronucleus ( M.P.N .) 
cannot be seen, but the latter has penetrated further into the 
egg. In all the sections of newly laid eggs that I have found, 
the cytoplasm towards the central region of the egg has 
become partially vacuolated and thinner, while the germ cell 
determinant has become much more faintly staining. My 
collection of newly laid eggs is not complete enough to show 
whether this thinning out of the central region of the egg is 
the rule, and it should be observed that in PI. 11, fig. 11, 
which shows the formation of the polar bodies, this vacuolisa- 
tion was quite absent. In PI. 11. fig. 7, I have drawn a 
transverse section of an egg which shows the nucleus lying 
in a central clear region, and quite close a denser part 
of the cytoplasm containing a cloud of granules ( Q.G . ). 
The egg, when laid, lies almost always towards the top of 
the Donacia ovum, and it never has a definite orientation, for 
in a section of a group of the host's eggs one cuts across eggs 
in all directions. In a brood of parasites which I caught 
emerging, some had their heads downwards in the Donacia 
egg, some their abdomens. At the stage when the larva 
begins to feed, it is forced to lie lengthwise in the host’s egg; 
because it has by then become too long to lie in any other 
way. It is obvious that the orientation of the pupating 
Trichogramma larva in relation to the Donacia egg is not 
governed by any special circumstance. Nevertheless it is 
possible, though to my mind unlikely, that the larva may be 
able to turn around at will witbin the Donacia egg. 
The newly laid egg is provided with a vitelline membrane 
and a thin chorion ( G.H . ). 
Formation of the Polar Bodies. 
In the one egg I found at this stage there were two polar 
bodies (PI. 11, fig. 11). One polar body ( P.B b) has been 
