50 THE BRITISH W00DLICE. 



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 w r oodlouse 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 



