twisted. Towards the end of the last larval stage, the cells of the
inner coat (epithelium) lining the stomach begin to undergo
degeneration, small replacing cells appearing between their bases and
later giving rise to the more delicate epithelium that lines the mid-gut
of the imago. The larval cells are shed into the cavity of the stomach
and become completely broken down. J. Anglas (1902), describing these
microscopic changes in the transformations of wasps and bees, has shown
that the tiny replacing cells can be recognised in sections through the
digestive canal of a very young larva; they may be regarded as
representing imaginal buds of the adult gastric epithelium. In the
transformations of two-winged flies of the bluebottle group, A.
Kowalevsky (1887) has shown that these replacing cells are aggregated in
little masses scattered at different points along the stomach and thus
corresponding rather closely to the imaginal discs of the legs and
wings.

The gullet, crop, and gizzard of an insect, which lie in front of the
stomach, are lined by cells derived from the outer skin (ectoderm) which
is pushed in to form what is called the 'fore-gut.' Similarly the
intestine and rectum, behind the stomach, are lined with ectodermal
cells which arise from the inpushed 'hind-gut.' The larval fore- and
hind-guts are broken down at the end of larval life and their lining is
replaced by fresh tissue derived from two imaginal bands which surround
the cavity of the digestive tube, one at the hinder end of the fore-gut,
and the other at the front end of the hind-gut. The larval salivary
glands in connection with the gullet are also broken down, and fresh
glands are formed for the imago.

A large part of the substance of an insect larva consists of muscular
tissue, surrounding the digestive tube, and forming the great muscles