50
THE BRITISH WOODLICE.
walking legs makes its appearance, and Mr. James B. Casserley
[whose work one of us (75) has described elsewhere] found when
keeping a number of the common pill-woodlouse (Armadillidium
vulgare) in captivity that his specimens did not subsequently
change their skins more than once in the six months during
which he had them under observation. He also noted that the
crustaceans go on growing after they are sexually mature. As
his specimens grew older, Mr. Casserley noticed that their colour
became darker, and a curious point recorded by him is that two
examples of the same age may change their skins at the same
time, and while one may have afterwards nearly twice as many
markings, on the other very few at all will be seen. The time
required for the growth of a Woodlouse from the size of a pin's
head to that of an adult example—say three-quarters-of-an-inch
long—must be fairly considerable, taking into account the fact
that any appreciable increase in size can only occur at a moult
and Mr. Casserley's observations as to the infrequency of the
process in Armadillidium vulgare.
Habits and Economic Considerations.—The con-
struction of the breathing organs of woodlice, and the necessity
which exists for these to be kept moist, restricts the habitats of
the animals considerably. Woodlice are found under stones and
logs, beneath the bark of dead and rotten trees, among decaying
vegetable matter as well as living grass and moss in damp or
wet situations. When looking for some of the common species
under the bark of fallen trees it is surprising to notice that the
crustaceans may be entirely absent from many trunks, while
when another is examined which seems to differ very slightly, if
at all, in condition or situation, they are found in swarms. There
is no doubt but that the habits of woodlice would well repay the
attention of naturalists, who are now recognizing that besides
anatomy as such, and the classification which a knowledge of
structure permits, there is the equally important consideration of
the creatures as they live their own life and affect that of others.
It is not our object to give a detailed account of the ecology of
British woodlice, but rather to provide a basis from which it may
be approached. Nevertheless a few general remarks may not
come amiss. Many points in the life-history of woodlice may
no doubt be learned by keeping them in captivity and there is