300 
STRANGE DWELLINGS . 
closely allied to the ichneumon flies which have just been 
described. 
Running to and fro upon the leaf, she fixes upon one of the t 
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 magnifying 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 which the insects have escaped, showing 
that they had attained their full size. On the juices of the gall ! 
the enclosed insect lives, until it reaches its full term of im- 
prisonment, when it eats its way through the gall and emerges 
into the world. In some cases, it undergoes the whole of its 
change within the gall, but in others, it makes its way out while 1 
