two modes of development is furnished by the
position of the wing-rudiments. In all Ametabola and Hemimetabola these
are visible externally long before the penultimate instar has been
reached; in the Holometabola they are not seen until the pupal stage.

Attention has already been drawn to the contrast in outward form between
a butterfly and its caterpillar. As in the case of dragon-fly or
may-fly, the larval period is essentially a time for feeding and growth,
and during this period the larval cuticle is cast four or five, in some
species even seven or eight times. After each moult some changes in
detail may be observable, for example in the proportions of the
body-segments or their outgrowths, in the colour or the closeness of the
hairy or spiny armature. But in all main features the caterpillar
retains throughout its life the characteristic form in which it left
the egg. From the tiny, newly-hatched larva to the full-fed caterpillar,
possibly several inches in length, there is all along the same crawling,
somewhat worm-like body, destitute of any outward trace of wings. When
however the last larval cuticle has split open lengthwise along the
back, and has been worked off by vigorous wriggling motions of the
insect, the pupa thus revealed shows the wing-rudiments conspicuous at
the sides of the body, and lying neatly alongside these are to be seen
the forms of feelers, legs, and maxillae of the imago prefigured in the
cuticle of the pupa (fig. 1 _e_). The pupa thus resembles the imago much
more closely than it resembles the larva; even in the proportions of the
body a relative shortening is to be noticed, and the imago of any insect
with complete transformation is reduced in length as compared with the
full-fed larva. Now these wings and other structures characteristic of
the imago, appear in the pupa which is revealed by the shedding of the
last larval cuticle. From these facts we infer that the wing-rudiments
must be present in the larva, hidden beneath the cuticle; and until the
last larval instar, not beneath the cuticle only, but growing in
such-wise that they are hidden by the epidermis. For if they were
growing outwardly the new cuticle would be formed over them, so that
they would be apparent after the next moult. But it is clear that only
in the pupa, forming beneath the cuticle of the last larval instar, can
they grow outwards.

Anatomical study of the caterpillar at various stages verifies the
conclusions