THE BRITISH WOODLICE. 51
just sufficient difficulty in doing this successfully to give an
interest to the matter.
Apart from a supply of proper food, we take it that the chief
object to be attained is the provision of the amount of moisture
required by the particular species under examination, together
with a sufficient supply of air.
A great many interesting observations can be thus carried
out, such as those of Mr. Casserley, to which allusion has already
been made. The process of moulting for instance is well worth
watching, and although specimens with half their coat changed
may be found in remote corners, yet the whole course of the
moult can be seen much better in the case of captive woodlice.
The following account is taken from Mr. Casserley's description
(75) of what happens in the case of Armadillidium vulgare :—The
approach of the moult is indicated by the appearance of a white
border on each segment of the body, which becomes gradually
more marked, while at the same time the animal is seen to be
less active and often makes a small burrow in which to hide.
Sometimes a sheltered corner against a stone is looked upon as
affording sufficient protection, but in either case each Woodlouse
keeps to the place originally chosen. About ten days after the
white lines have become visible the animal appears to be divided
into two. Its skin is becoming loose and little movement can
take place at the joints of its body with the exception of that
between the fourth and fifth thoracic segments where the skin
will ultimately break. The Woodlouse spends a day or two in
this condition and then, by suddenly walking forward, frees itself
from the covering of the hinder portion of its body The three
last pairs of walking legs are carefully pulled out from the old
skin, which now appears perfectly white, and at the same time
the lining of the hind portion of the alimentary canal (hind gut)
is also shed. After putting the tender half of his body well into
his corner or burrow the Woodlouse proceeds to eat the part of
his skin that he has cast. The creature has now a very odd
appearance. His front half with the exception of the white
edges is as it was before, the rest of him instead of a light slaty
blue, and is very soft as well as proportionately a little larger.
In three days or so the tail end becomes hard and attains the
normal colour. Then the old skin from the front half is pushed
off and the creature becomes practically defenceless, so much