78 



SEA-SHORE LIFE 



hard skin-armor of the body affords excellent attachment for the 

 muscles, and it is well known that in proportion to their size in- 

 sects and crustaceans are the strongest of all animals. It has even 

 been calculated that if a inan possessed muscles as strong in propor- 

 tion as those of a flea he could readily leap over St. Paul's Cathedral. 



f 



Fig. 46; YOUNG ROCK-CRAB. From life, natural size. Showing tlie rapid enlargement 



that tooli place after the shell was uioiilted. The Crab had lost oueof its nippers, 



but this was regenerated after the moult. 



Being encased in a natural armor crustaceans can not grow at 

 a uniform rate, but enlarge suddenly at the periods when the shell 

 is shed. This occurs at fairly regular intervals, and the entire 

 shell is shed, even the coverings of the eyes and part of the lining 

 of the stomach being cast off. The creature is then soft and helpless, 

 and usually remains hidden in some safe retreat until the body has 

 expanded and the new shell hardened. 



The appendages of crustaceans are of various sorts such as 

 feelers, mouth parts, claws, legs, egg-carrying organs, swimming and 

 breathing organs, and stalked eyes. 



The Crustacea are divided into two sub-classes, the lowest 

 called the Entoniostvaea, the barnacles and water fleas, have a var- 

 iable number of body segments, and the appendages are usually 

 forked, and are apt to be quite similar each to each. The higher 

 sub-class called the Malacostraca includes the crabs, lobsters, 

 shrimps, and sand fleas. Their bodies consist of twenty segments; 

 five in the head, eight in the middle part of the body, and seven in 

 the abdomen; and their ajDpendages are apt to be dissimilar each 

 from each. 



