caterpillar of a butterfly is obliged to do.

[Illustration: Fig. 18. Young Larva (_FL_), Full-grown Larva (_SL_) and
Pupa (_N_) of Hive-bee (_Apis mellifica_). _co_, cocoon; _sp_,
spiracles; _ce_, eye; _an_, feeler; _m_, mandible; _l_, labium.
Magnified 4 times. After Cheshire, _Bees_.]

Among those saw-flies whose larvae feed throughout life in a concealed
situation, we find an interesting transition between the caterpillar
and the legless grub. For example, the giant saw-flies (so called
'Wood-wasps') have larvae that burrow in timber, and these larvae
possess relatively large heads, somewhat flattened bodies with pointed
tail-end, and very greatly reduced legs. The feeble legless grub,
characteristic of the remaining families of the Hymenoptera, is provided
for in a well-nigh endless variety of ways. The female imago among these
insects is furnished with an elaborate and beautifully formed
ovipositor, and the act of egg-laying is usually in itself a provision
for the offspring. Gall-flies pierce plant-tissues within which their
grubs find shelter and food, the plant responding to the irritation due
to the presence of the larva by forming a characteristic growth, the
_gall_, pathological but often regular and shapely, in whose hollow
chamber the grub lives and eats. Ichneumon-flies and their allies pierce
the skin of caterpillars and other insect-larvae, laying their eggs
within the victims' bodies, which their grubs proceed to devour
internally. Some very small members of these families are content to lay
their eggs within the eggs of larger insects, thus obtaining rich
food-supply and effective protection for their tiny larvae. In
Platygaster and other genera of the family Proctotrypidae, M. Ganin
(1869) showed the occurrence of hypermetamorphosis somewhat like that
already described as occurring among the Oil-beetles (Meloidae). The