to ON THE ORIGIN AND [CHAP. 



the sawfly, but resembling a needle. With this she 

 stings or punctures the surface of leaves, buds, stalks, 

 or even roots of various plants. In the wound thus 

 produced she lays one or more eggs. The effects of 

 this proceeding, and particularly of the irritating fluid 

 which she injects into the wound, is to produce a 

 tumour or gall, within which the egg hatches, and on 

 which the larva, a thick fleshy grub (Plate II., Fig. 7), 

 feeds. In some species each gall contains a single 

 larva; in others, several live together. The oak 

 supports several kinds of gallflies : one produces 

 the well-known oak-apple, one a small swelling on 

 the leaf resembling a currant, another a gall some- 

 what like an acorn, another attacks the root ; the 

 species making the bullet-like galls, which are now 

 so common, has only existed for a few years in this 

 country ; the beautiful little spangles so common 

 in autumn on the under side of oak-leaves are the 

 work of another species, the Cynips longipennis. 

 When the larva is full-grown, it eats through the gall, 

 falls to the earth, and turns into a chrysalis. One 

 curious point about this group is, that in some of 

 the commonest species the females alone are known, 

 no one yet having ever succeeded in finding a 

 male. 



Another great family of the Hymenoptera is that 

 of the ichneumons ; the females lay their eggs either 

 in or on other insects, within the bodies of which the 

 larvae live. These larvae are thick, fleshy, legless 

 grubs, and feed on the fatty tissues of their hosts, 

 but do not attack the vital organs. When full- 

 grown, the grubs eat their way through the skin of 



