74 



CRABS. 



some, the abdomen is very short, and folded beneath the thorax 

 (Jig- 63); while in others, this part of the body extends back- 

 wards, is of considerable size, and is a powerful organ of loco- 

 motion (fig. 61, page 69). 



2. This order is divided into the Macrou'ra (from the Greek, 

 makros, long, and oura, tail) or swimming decapods, which have 

 a long abdomen terminated by a fin spread out like a fan (fig. 

 61, c); the Bra'chyu'ra (from the Greek, brachus, short, and 

 oura, tail) or short-tailed species, of which the crab is a familiar 

 specimen ; and the Anomou'ra (from the Greek, anomos, name- 

 less, irregular, and oura, tail), which inhabit the empty shells of 

 mollusks. 



3. The section of BRA'CHYU'RA consists of crusta'ceans, known 

 under the common name of crabs ; they are formed for running, 

 rather than swimming. This section is divided into four families, 

 each of which is composed of several tribes, subdivided in turn 

 into a great many genera ; they are esteemed as food. Most of 

 them inhabit the sea. They run quickly along the shore ; their 



legs are placed in 



bed e suc h w i se that they 



most easily move 

 sideways, although 

 they can advance in 

 any direction. The 

 first pair of legs are 

 pincers or claws, and 

 do not assist in loco- 

 motion. 



4. Among the 

 common species, on 

 the French coast, 

 is one, sometimes 

 known as the mad 

 crab, Cancer mcenas, 

 from its manner of 

 running ; it is of 

 moderate size, and 

 the carapace is 



Explanation of Fig. fi3. A crab (Cancer pagvrus) ; a, the carapace; 

 6, the eyes ; c, the external antennae ; d, the internal antennse ; e, the 

 rhelce or pincers ; /, second pair of legs ; g, the abdomen, folded beneath 

 the thorax. 



2. How is the order of Decapoda divided ? 



3. What crusta'ceans are comprised in the section Bra'chyu'ra ? How 

 are crabs characterized ? 



4. How does the mad crab obtain its name 1 



Fig. 63. CRAB. 



