DEVELOPMENT OF TR1CHOGRAMMA EVANESCENS. 155 
the chorions of the neighbouring eggs, all of which were 
parasitised. 
It will be seen that when these eggs were attacked the 
contained embryos had become far advanced and were almost 
ready to hatch. Though one can observe a Donacia ovi- 
positing, and a parasite on the same mass piercing and 
depositing its eggs in the newly laid beetle's eggs, it is 
possible to find eggs parasitised at any stage. If one removes 
Donacia embryos from their chorion by means of fine needles 
and stains them in paracarmine, one can often find the 
developing parasites as in PI. 10. fig. 2, at _D.P. Now this 
embryo lies at the posterior pole of the embryo beetle, and is 
too far down to have been oviposited there. It may be that 
this egg was an outside one of the mass and that the parasite 
bored it from the side ; but such cases occur too frequently 
in sections of eggs in the middle of the mass, and I am 
inclined to think that in those Donacia eggs laid in a 
horizontal position the developing Trichogramma embryo 
may sink downwards. I cannot otherwise explain how 
parasites* eggs are found in this position, because the beetle's 
eggs seem too closely applied to one another to allow the 
parasite to get its ovipositor between them, and reference 
to PI. 10, fig. 1, will show how short the little insect's 
ovipositor is. (Both fig. 1 and 2 are drawn to the same 
scale: x 75.) 
The Effect of the Deposition of the Egg in the 
Developing Embryo's Body. 
Primarily the effect is to arrest further development of the 
host, but all life is not killed immediately, for living nuclei 
are to be found much later on as the parasite develops. As 
is well known, the nuclei in the yolk of an insect's egg are 
very large, and such vitellophags become larger than the 
other cells almost from the time they are established. I 
believe that it is the vitellophags which manage to live longest 
after the parasite has oviposited in the beetle's egg, and in 
