152 ELEMENTARY ZOOLOGY 



and the front portion of the body is covered by a horny 

 fold of the body-wall called the carapace. 



The lobsters are large ocean-inhabiting crustaceans 

 which are very like the fresh-water crayfish in all struc- 

 tural characters. They live on the rocky or sandy ocean- 

 bottom at shallow depths. They feed largely on decaying 

 [ animal matter. They are caught in great numbers in 

 so-called " lobster pots, " a kind of wooden trap baited 

 with refuse. "The number thus taken upon the shores 

 of New England and Canada amounts to between twenty 

 and thirty million annually. " Live lobsters are brownish 

 i or greenish with bluish mottling; they turn red when 

 boiled. A single female will lay several thousand eggs. 

 The eggs are greenish and are carried about by the mother 

 until the young hatch. The young are free-swimming 

 larvae, until they reach a length of half an inch. 

 ^j The shrimps and prawns are mostly marine, though* 

 some species live in fresh water. They are, like the 

 lobsters, used for food. Some of the species are gregari- 

 ous in habit, occurring in great " schools " of individuals. 

 Like the lobsters they crawl about on the sea-bottom 

 feeding on decaying animal matter. Shrimps are very 

 abundant near San Francisco, where extensive "shrimp 

 fishing " is done by the Chinese. 



.JkThe crabs (fig. 37) differ from the lobsters and cray- 

 fishes and shrimps in having the body short and broad, 

 instead of elongate. This is due to the special widening 

 of the carapace and the marked shortening of the 

 abdomen. The abdomen, moreover, is permanently bent 

 underneath the body, so that but little of it is visible from 

 the dorsal aspect. The number of abdominal legs or 

 appendages is reduced. When the tide is out the rocks 

 and tide-pools of the ocean shore are alive with crabs. 

 They "scuttle " about noisily over the rocks, withdraw- 

 ing into crevices or sinking to the bottom of the pools 



