238 NATURAL HISTORY. 
their skins repeatedly. The Silkworm and other cater- 
pillars cast their skins about four times during their 
growth. 
409. Insects pass the time of their pupa state under 
various circumstances. Some, when about going into 
this state, crawl into some by-place away from intruders. 
Some work their way into the ground, and perhaps spin 
a silken lining for the earth-cells in which they are to 
sleep through their change. Some roll themselves up in 
leaves. Some construct for themselves a silken house, 
called a cocoon, attached to some leaf or twig. 
410. Among those that do this last is the Silkworm. 
The formation of the cocoon I will describe. When the 
worm has its silk factory, which is near its mouth, prop- 
erly stocked with the gummy pulp from which the silk 
is to be spun, it seeks a good place where it can have a 
sort of scaffolding for its cocoon. It first spins some 
loose floss, attaching it to things around. Next it be- 
gins to wind its silk round and round, making a cocoon 
at length, shaped much like a pigeon’s egg, being smaller 
at one end than the other. It thus gradually shuts itself 
up in a silken prison. The last of the silk which it spins 
is the most delicate of all, and it is well glued together, 
making a very smooth surface next to the Silkworm’s 
body. The silken house being constructed, it now pre- 
pares itself for its sleep and its change. It sheds its skin 
now for the fourth and last time, tucking its old clothes, 
as We may say, very snugly at one end of the cocoon. It 
then passes into its sleep, and a new and thin skin is 
formed over it, in which it gradually changes into an an- 
imal endowed with wings. At the proper time it works 
its way out of its prison, unfolds its wings, and flies off, 
not to eat mulberry leaves, as it did in its larva state, but 
to sip the honey from the flowers. 
411. Observe the manner of its exit and the arrange- 
ments for it. The head is always at the small end of the 
cocoon, and here the silk is less closely wound and less 
