adult; and the greater these differences, the more profound must be the
changes that mark the pupal stage.

From the prominence of imaginal structures in the pupa, it is at once
seen that the pupa of any insect must resemble the adult more nearly
than it resembles the larva. But in different groups of insects we find
different degrees of likeness between pupa and imago. In a beetle pupa
(see fig. 16 _c_), the appendages--feelers, jaws, legs, wings--stand out
from the body as do those of the perfect insect. This type is called a
_free_ pupa. The pupal cuticle has to be shed for the emergence of the
imago, but the pupa is already a somewhat reduced model of the final
instar, with abbreviated wings and doubled-up legs. A free pupa is
characteristic of the Coleoptera, Neuroptera, Trichoptera, Hymenoptera
and many Diptera. In some cases the pupa requires to be specially
adapted for a peculiar mode of life; for example, a special arrangement
of breathing organs may be necessary for life under water, and there
must needs be temporary pupal structures, not represented in the imago.

On the other hand, in the pupae of most Lepidoptera and of some Diptera,
there is more or less coalescence between the cuticle of the appendages
and the cuticle of the body generally, so that the appendages do not
stand out, but being, as it were, glued down to the body, are somewhat
masked (see fig. 1 _e_ and fig. 23). Consequently the _obtect_ pupa, as
this type is called, does not resemble its imago as fully as a free pupa
does. The outline of the wings for example in a butterfly's pupa can in
some cases be traced only with difficulty. T.A. Chapman has shown (1893)
that the completely obtect pupa characterises the more highly developed
families of Lepidoptera, while in the more primitive families the pupa
is incompletely obtect. If the pupa of a butterfly or moth be lifted and
held in the hand, a bending or wriggling motion of the abdomen can be