relatively far-separated ganglia into the shortened, condensed
nerve-cord of the Tortoise-shell butterfly (_Vanessa urticae_) with
several of the ganglia coalesced. In many Diptera, on the other hand,
the nervous system of the larva is more concentrated than that of the
imago.

The tubular heart also of a winged insect is the directly modified
survival of the larval heart.

Similarly the reproductive organs undergo a gradual, continuous
development throughout an insect's life-story. Their rudiments appear in
the embryo, often at a very early stage; they are recognisable in the
larva, and the matured structures in the imago are the result of their
slow process of growth, the details of which must be reckoned beyond the
scope of this book. For a full summary of the subject the reader is
referred to L.F. Henneguy's work (1904) containing references to much
important modern literature, which cannot be mentioned here.

On the other hand, the digestive system of insects that undergo a
metamorphosis, passes through a profound crisis of dissolution and
rebuilding. This is not surprising when we remember that there is often
a great difference between larva and imago in the nature of the food.
The digestive canal of a caterpillar runs a fairly straight course
through the body and consists of a gullet, stomach (mid-gut),
intestine, and rectum; it is adapted for the digestion of solid food. In
the butterfly there is one outgrowth of the gullet in the head--a
pharyngeal sac adapted for sucking liquids; and another outgrowth at the
hinder end of the gullet (which is much longer than in the larva)--a
crop or food-reservoir lying in the abdomen. The intestine of the
butterfly also is longer than that of the larva, being coiled or