500 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 

 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 ^gg, precisely the same as that which takes 

 place when a wasp uses its sting, the ovipositor and sting 

 being but two slightly diff'erent 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 wcrld. In some cases, it undergoes the whole of its 

 change within the gall, but in others, it makes its way out while 



