ARTHROPODS AND MOLLUSCS 151 



shallow pools, in which places the dried-up skeletons are 

 noticeable during the summer months. 



For an exhaustive account of the biology of the crajrfish see Huxley's 

 "The Crayfish: An Introduction to Zoology." 



Lobsters are very much like crayfish in all structural char- 

 acters, although much larger. They live on the rocky 

 sandy ocean-bottom at shallow depths. 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 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- 

 swimming larvse until they reach a length of half an inch. 



Most crabs (fig. 62) differ from the lobsters, craj^shes, 

 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 back- 

 ward or sidewise, "crab-fashion," as forward. They are 

 of various colors and markings, often so patterned as to 

 harmonize very perfectly with the general color and appear- 

 ance of the rocks and sea-weeds among which they live. 

 The spider-crabs are especially strange-looking creatures, 

 with unusually long and slender legs and a comparatively 

 small body-trunk. They include the Macrocheira of Japan, 

 the largest of the crustaceans. Specimens of this crab are 



