OF THE SAW-FLIES (tENTHREDINID^). 129 



July. They are of a pale dull green colour, covered en- 

 tirely with minute white tubercles which gives them a 

 whitish appearance. The head is of a pale straw colour, 

 more orange on the crown, with a small black spot on each 

 side, in the middle of which is a single eyelet. The dis- 

 charges of green watery fluid from the pores of the sides of 

 the body can be repeated several times. The object is 

 evidently to deter parasitic enemies, in which, however, it 

 is often unsuccessful, as, not unfrequently, I have found the 

 interior of the cocoon filled with the smaller cocoons of 

 Ichneumon parasites, which have lived within the body of 

 the larva, the shrivelled remains of which might be seen 

 lying at one end of the cocoon. 



I have, in fact, obtained two distinct species of Ichneu- 

 monidce from one cocoon of the Trichiosoma, and from 

 another cocoon I have obtained specimens both of an Ich- 

 neumon and of a Pteromalus. On opening the cocoons 

 during the winter month, each is generally found to con- 

 tain a large green caterpillar rolled up, its head and tail 

 being brought almost into contact, but about the end of 

 April the insect assumes its pupa state, in which it is 

 generally reduced in its length, and exhibits all the parts 

 of the perfect insect, the antennae and legs lying upon the 

 breast, each enclosed in a distinct membranous case, and 

 the wings of a small size encased in oval sheaths at the sides 

 of the body. On comparing the pupa with the chrysalis 

 of any species of moth, we find there is a complete difference, 

 not only in the way in which the limbs are enclosed under 

 a general covering in the moths, while each has a distinct 

 covering in the Trichiosoina-\mp&, enabling the insect to 

 move each limb separately when ready to assume the 

 perfect state, but, also, that the head of the pupa of the 

 Trichiosoma is also distinct, and furnished with a pair of 



1858 K 



