12 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 (Avmadillidium 
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. (See p 14.) 
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 providea 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 
