6 



lies naked in that. A small minority of species feed on the- 

 outside of their prey, sucking the juices through the skin. 



The grubs of the Ichneumon Flies being for the great part 

 internal feeders, are naturally very seldom seen; the case most 

 often observed, perhaps, is when a large number of small white 

 maggots are found emerging through the skin of a Cabbage 

 Butterfly caterpillar to spin a bunch of white or yellowish- 

 white cocoons (Plate I., Fig. la) on the leaf near-by, from each 

 of which will emerge in due course a small black Ichneumon 

 (Braconid) (Plate I., Fig. 7). 



The Pupa is like the perfect insect to be, but covered with 

 a fine white skin on all its parts, the whole creature being white 

 until some days before emergence from this pupal covering, 

 when the colours it will eventually assume gradually appear, 

 starting with a darkening of the eyes. 



The Perfect Insect. On the pupal skin splitting and being 

 worked off backwards like a glove, the perfect insect is disclosed 

 with all its parts free. At first it is soft and does not come 

 forth like a butterfly to dry, but remains some time within the 

 cocoon until all its parts have hardened, when it eats a way 

 out, and, having paired, the female begins to hunt for the prey 

 to which she is attached and in or upon which she lays eggs. 

 The structure of the adult Ichneumon Fly varies according to 

 the kind of insect in which the early stages are spent. The 

 difference is most marked in the length of the egg-laying 

 apparatus or ovipositor. There are some species in which this 

 has been carried to an extreme degree, where it is necessary 

 to reach caterpillars in such places as their burrows in the 

 interior of a tree; in other species (Plate I., Fig. 9) it is of 

 medium length and stout for piercing through cocoons and 

 into the chrysalid contained therein. Parasites such as these 

 never see the hidden victim that is to contain their egg, but v 

 nevertheless, are marvellously acute in " sensing " all about it, 

 detecting at once its age, position, and whether it already 

 contains an egg from another individual. Parasites of cater- 

 pillars met with in the open, and directly upon which the insect 

 settles to lay its egg, naturally have quite short ovipositors 

 (Plate I., Fig. 6). 



Ichneumons, which are parasites of the eggs of other insects, 

 are, of course, very small, the tiny egg serving as a cocoon. 

 It is not uncommon for a small Ichneumon to emerge from 

 every egg in a batch of the Vapourer Moth. It was once thought 

 that every insect had its Ichneumon parasite attached to it 

 and that the Ichneumon confined itself to that one species,. 

 but now quite long lists of different victims are accredited to 

 single species of Ichneumon Flies. This does not mean that 

 any Ichneumon parasitises any other sort of insect it comes 

 across far from it. The parasite's life-history is very closely 

 bound up with that of its victim, and it is only such insects 

 as will so accord with its own life-history and its own peculiar 



