e ancestral stock of all these insects must have been the
interior of plant tissues. He is thus forced to the necessity of
suggesting that the campodeiform larvae of ground-beetles or lacewings
must be regarded as due to secondarily acquired adaptations; 'they
resemble Thysanura and the larvae of Heterometabola only as whales
resemble fishes.' There are two considerations which render these
theories untenable. The Neuroptera and Coleoptera among which
campodeiform larvae are common, are less specialised than Lepidoptera,
Hymenoptera, and Diptera, in which they are unknown. And among the
Coleoptera which as we have seen (pp. 50 _f._) display a most
interesting variety of larval structure, the legless, eruciform larva
characterises families in which the imago shows the greatest
specialisation, while in the same life-story, as in the case of the
oil-beetles (pp. 56-7), the newly-hatched grub may be campodeiform,
changing to the eruciform type as soon as it finds itself within reach
of its host's rich store of food.

A certain amount of difficulty may be felt with regard to the theory of
divergent evolution between imago and larva, in the case of those
insects with complete transformation whose grubs and adults live in much
the same conditions. By turning over stones the naturalist may find
ground-beetles in company with the larvae of their own species. On the
leaves of a willow tree he may observe leaf-beetles (Phyllodecta and
Galerucella) together with their grubs, all greedily eating the foliage;
or lady-bird beetles (Coccinella) and their larvae hunting and devouring
the 'greenfly.' All of these insects are, however, Coleoptera, and the
adult insects of this order are much more disposed to walk and crawl and
less disposed to fly than other endopterygote insects. Their heavily
armoured bodies and their firm shield-like forewings render them less
aerial than other insects; in many genera the power of flight has been
altogether lost. It is not surprising, therefore, that many beetles,
even when adult, should live as their larvae do; since the acquirement
of complete metamorphosis they have become modified towards the larval
condition, and an extreme case of such modification is afforded by the
wingless grub-like female Glow-worm (Lampyris).

With most insects, however, the larva must be regarded as the more
specially modified, even if degraded, stage. Miall (1895) has pointed
out that the insect grub is not a precociously