nown as 'moulting.' At each change of skin a
sudden and easily noticed increase of size takes place; and, before
further growth is possible, another moult must be undergone.

Directly after each moult the body will be found to be quite soft, but
the skin quickly hardens again.

The manner in which the 'old clo'' are cast off is curious. For some
time before the change takes place, the insect appears to 'sicken,'
taking no food and wearing a very mournful air. At last it wakes up into
something like activity. Now is the time to watch. If--in the case of a
silkworm, for example--the watching is begun a little earlier than this,
it will be found that the day before the change, the insect deliberately
binds its hinder legs to the leaf on which it rests by silken threads.
This done, it remains motionless. Soon after, through the transparent
skin, a second head, larger than the first, will be seen; then the body
is raised, and the skin is separated from it by the formation of a fluid
which circulates between the old skin and the body. Next, by a series of
vigorous movements, the old skin cracks along the back, and the insect
first pushes out its head and the fore-part of the body, and then
withdraws the hinder part. In a few minutes all is over, and the old
skin is left bound to the leaf by the silken threads. How complete this
change is may be seen from the fact that even the breathing tubes and
the inner lining of the digestive organs are cast off.

This process, in the case of the caterpillar, takes place no less than
four times--in some caterpillars five times. Ten days separate each of
the first four moults, and an interval of sixteen days elapses between
the fourth, or fifth, and last. This last moult is followed by a still
greater change, the caterpillar passing into a state of coma, or sleep,
during which it is turned into the butterfly or moth. For this purpose
it spins a winding-sheet of silk, or digs down into the ground and forms
a case, or cocoon; or else it hangs itself by the tail, and becomes
strangely transformed into what we call a 'chrysalis.' From the cocoon,
or chrysalis, as the case may be, the butterfly or moth sooner or later
makes its appearance.

[Illustration: Fig. 1.--Dragon-fly moulting.]

To give an idea of the great increase of growth in insects, let us take
the case of the silkworm. At the time of hatching, the little worm
weighs about the one-hundredth part of a grain; when fully grown, it