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CHAPTER XIX. 



THE CRUSTACEA. 



" Multa tamen Ijetus tristia pontus habet." — Ovid. 



We divide the Arthropods into four classes, the Insects, 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 trachese, 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 {q.\v, like some insects, have eyes both 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 {Carcimis mcenas, Leach) loves the shore almost as much as the 



