CH. XII.] THE ICHNEUMON-FLY. 209 



sects either nourish their young themselves, or place 

 them in the midst of an element which contains the 

 food which they require ; but these present the ano- 

 maly of cradling their offspring in the living bodies 

 of other insects. 



They vary in size, from the minutest to the largest 

 among insects. They deposite their eggs some- 

 times on the outside, but mostly on the inside of the 

 insect which they attack ; and it is only to the three 

 first insect forms of egg, larva, and pupa that they 

 choose to commit their offspring. By means of their 

 long ovipositor they pierce the cell of the gall-fly, or 

 the nest of the solitary and the social humble bee ; in 

 short, when pressed to lay their eggs, nothing can 

 escape them. Neither the vigilance of the parent 

 nor the solidity of the habitation can defend the 

 young of other insects from their attacks. These 

 grow up just so long as is requisite to supply the 

 young ichneumon which is feeding on their vitals ; 

 and when it is ready to emerge, they die. 



Those which are obliged to pierce the nests of in 

 sects, in order to deposite their eggs, are provided 

 with a long ovipositor ; those which simply pierce 

 the insect itself have only short ones. 



Fig. 1. The ichneumon fly, with its ovipositor. 



2. The ovipositor, seen to consist of three pieces. 



3. The centre piece or tube through w hich the egg is trans- 



mitted. It is serrated at the end, and the two lines which 

 run from it ought to have represented a string of mucus, 

 which is lodged with the egg, wherever the latter is de- 

 posited. 



S2 



