106 SOCIAL HABITATIONS. 
her to belong to the order hymenoptera, and to be 
closely allied to the ichneumon flies which have just been 
described. 
Running to and fro upon the leaf, she fixes upon one 
of the nervures, and there remains for a short time, 
evidently busy about some task, which is very important 
to her, but which her minute size renders impossible to 
be observed with the naked eye. If, however, a mag- 
nifying glass be applied very carefully to the leaf, the 
following process will be seen. 
From the abdomen there projects a tiny hair-like 
ovipositor, which is coiled in such a manner that it can 
be protruded to a considerable length, This ovipositor 
is thrust into the leaf; so as to produce a hole, which 
is widened by the action of the boring instrument. 
Presently, the blades of the ovipositor separate, and a 
single egg is seen to pass between them, so that it is 
lodged at the bottom of the hole. Into the same aperture 
is then poured a slight quantity of an irritating fluid, 
and the insect flies away, having completed her task. 
The whole proceeding, indeed, is, with the exception of 
the deposition of the egg, precisely the same as that 
which takes place when a wasp uses its sting, the 
ovipositor and sting being but two slightly different 
forms of the same organ, and the irritating fluid of the 
cynips being analogous to the poison of the wasp. 
The effect of the wound is very remarkable. The 
irritating fluid which has been projected into the leaf has 
a singular effect’ upon its tissues, altering their nature, 
and developing them into cells filled with fluid. As long 
as the leaf continues to grow, the gall continues to swell, 
until it reaches its full size, which is necessarily variable, 
being dependent on that of the leaf. I have, for example, 
many specimens of these galls, of different sizes, from 
