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CHAPTER XIX 
THE CRUSTACEA. 
‘Multa tamen leetus tristia pontus habet.”—OvIp. 
We divide the Arthropods into four classes, the Jnsecta, the Myria- 
poda, the Arachnida, and the Crustacea, and it is this last which 
must now engage our attention. It may, however, be proper to 
remark that we pass over here the large section of the ANNULOSA— 
animals, very many of which inhabit the sea; indeed, the classes 
Annelida and Gephyrea are almost exclusively marine. 
The Crustacea is the lowest division of articulate animals ; they 
possess feet ; they breathe by means of gills, and have no trachez, or 
air-passages, as in the Insecta. The name signifies a hard crust or 
covering, with which the animals are protected. This consists of 
layers of carbonate of lime with one of pigment, generally, but not 
always, on the surface. The general outline of these animals is 
peculiar ; unlike insects, they are not divisible into head, thorax, and 
abdomen ; many species truly have no apparent head ; but a pair of 
eyes point to the seat of intelligence. Most of these animals have two 
compound eyes ; but a few, like some insects, have eyes botlt simple 
and compound. The mouth is situated in the under part of the 
anterior of the body: in some cases they have jaws, as in crabs; in 
other suckers only. 
The Crustaceans have nearly all of them claws, formidably hooked 
and toothed, which they employ as pincers, both in offensive. and 
defensive war. They have been compared to the heavily-armed 
knights of the middle ages—at once audacious and. cruel’; barbed in 
steel from head to foot, with visor and corslet, arm-pieces and thigh- 
pieces—scarcely anything, in fact, is wanting to complete the re- 
semblance. 
These marine marauders live on the sea-coast, among the rocks, 
and near the shore. Some few of them frequent the deep waters, 
others hide themselves in the sand or under stones, while the common 
crab (Carcinus menas, Leach) loves the shore almost as much as the 
