ts of different
orders, it is worthy of notice that in some cases all the members of an
order have larvae remarkably constant in their main structural features,
while in others there is great variety of larval form within the order.
For example, the caterpillars of all Lepidoptera are fundamentally much
alike, while the grubs of beetles of different families diverge widely
from one another. A review of a selected series of beetle-larvae will
therefore serve well to introduce this branch of the subject.

[Illustration: Fig. 12. _a_, Carrion-beetle (_Silpha_) with its larva,
_b_. Magnified, _a_ 3 times, and _b_ 4 times.]

[Illustration: Fig. 13. Larva of a Ground-beetle (_Aepus_). Magnified
6 times. After Westwood, _Modern Classification of Insects_.]

Beetles are as a rule remarkable among insects for the firm consistency
of their chitinous cuticle, the various pieces (_sclerites_) of which
are fitted together with admirable precision. In some families of
beetles the larva also is furnished with a complete chitinous armour,
the sclerites, both dorsal and ventral, of the successive body-segments
being hard and firm, while the relatively long legs possess well-defined
segments and are often spiny. Such a larva is evidently far less unlike
its parent beetle than a caterpillar is unlike a butterfly. Perhaps of
all beetle larvae, the woodlouse-like grub (fig. 12 _b_) of a
carrion-beetle (Silpha) or of a semi-aquatic dascillid such as Helodes
shows the least amount of difference from the typical adult, on account
of the conspicuous jointed feelers. The larval glow-worm, however, is of
the same woodlouse-like aspect, and in this case, where the female never
acquires wings, but becomes mature in a form which does not differ
markedly from that of the larva, the exceptional resemblance is closer
still. In all beetle-grubs the legs are simplified, there being only one
segment (a combined shin and foot) below the knee-joint, whereas in the
adult there is a shin followed by five, four, or at least three
distinct tarsal segments. The foot of an adult beetle bears two claws
at its tip, while the larval foot in the great majority of families has
only one claw. In one section of the order, however, the Adephaga
comprising the predaceous terrestrial and aquatic beetles, the larval
foot has, like that of the adult, two claws. Some adephagous larvae,
notably those of the large carnivorous water-beetles (Dyticus), often
destructive to tadp