either heat or cold, none having ever been found productive after remaining for a time in the vacuum of an air-pump.
When the whole of the fluid in the interior of the egg has been assimilated, and the young larva matured, it emerges either by rupturing the envelope, gnawing it asunder, or pushing open a kind of moveable lid at the end, constructed apparently for the express purpose of facilitating its exit.
Larva. Insects as often present themselves to our notice in this stage of their existence as in their perfect state, and not unfrequently attract our attention by their depredations on the produce of our fields and gardens. In consequence of being so familiarly known, they are distinguished by a variety of popular names. Grubs are the larvæ of coleoptera; maggots, mawks, and gentles, those of diptera; and caterpillars the larvæ of butterflies, moths and saw-flies: the larvæ of most of the other races not differing materially in appearance from the matured insects, do not require a distinctive appellation in ordinary language. Lepidopterous larvæ, or the caterpillars of butterflies and moths, we have already described at considerable length[1]; those of beetles also have been occasionally noticed,[2] and the particular history of the other kinds will be afterwards given under their respective orders and families. The pre-
