154 FIRST LESSONS IN ZOOLOGY 



fish, see Huxley's "The Crayfish: An Introduction to 

 Zoolog)-. 



Lobsters and crabs. — Lobsters and crabs are not land 

 animals, as the)- live only in the ocean, but they belong 

 to the same class as the crayfish, and are therefore briefly 

 discussed here. The crayfishes, lobsters, crabs, pill -bugs 

 and water-fleas (described in the next section) all belong 

 to the class Crustacea of the branch ArtJiropoda. The 

 lobsters are very much like crayfish in all structural char- 

 acters, although much larger. The}' live c.i the rocky 

 sandy ocean-bottom at shallow depths. They are caught 

 in great numbers in so-called " lobster-pot^, " 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 or greenish, with bluish mottling; they turn 

 red when boiled. A single female will lay several thou- 

 sand eggs. They are greenish, and are carried about by 

 the mother until the young hatch. The young are free- 

 s\\'imming larvic- until they reach a length of half an inch. 



Most crabs (fig. i i 3) differ from the lobsters, crayfishes, 

 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 under 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 are alive with crabs. They " scuttle " about 

 noisily over the rocks, withdrawing into crevices or 

 sinking to the bottom of the pools when disturbed. They 

 move as readily backward or sidewisc, "crab-fashion," 

 as forward. They are of various colors and markings, 

 often so patterned as to harmonize \'ery perfectly with the 

 general color and appearance of the rocks anil sea-weeds 



