The pupa of a Lepidopterous insect is completely encased in a chitinous
envelope. With the exception of a slight twirling of the abdominal segments
it is incapable of any motion. In the pupa of _Micropteryx_ the mandibles
and labial palpi are said to be functionally active, but this is a very
exceptional though extremely interesting case. In conjunction with other
evidence it would appear to indicate that the _Lepidoptera_ originated from
insects with active pupæ. The number of free or movable segments of pupæ
varies considerably in different groups and genera, and by some modern
authors it is regarded as a character of much importance in the framing of
their classifications. The various organs of the perfect insect are
distinctly marked out on the otherwise uniform integument of the pupa. In
some groups, notably the _Micropterygina_, these organs are much more
distinctly indicated than in others.