ORDER DECAPODA. BRACHYOURA. 



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according to the development of the abdomen ; thedte are : 

 I. The BRACHYOURA, or short-tailed Decapods, to which the 

 name of Crabs is commonly applied ; II. The MACROURA, or 

 long-tailed, such as the Lobster, Cray-fah, &c. ; and III. The 



Fi. 579. CRAY-FISH ; a and b, antennae ; 

 e, eyes ; d, organ of hearing ; e, external 

 feet-jaws ; /, first pair of thoracic mem- 

 bers ; g, fifth pair of thoracic members ; 

 A, abdominal false-legs ; i, tail-fin ; ./, 

 anus. 



FIG. 580. MASTICATORY APPA RATUS, com- 

 posed of six pairs of appendages ; a, man- 

 dibles ; 6 and c, first and second pairs of 

 maxillae ; d, e, /, three pairs of feet-jaws, 

 gradually approaching the form of the or- 

 dinary limbs. 



ANOMOURA, in which the condition of the abdomen is inter- 

 mediate. Each of these sub-orders is divided into families ; 

 but it will be sufficient here to notice their principal forms. 



859. The BRACHYOURA may be considered as ranking at 

 the head of the whole Order, in regard to the concentration 

 and high development of their nervous, circulating, respiratory, 

 and secreting systems. They are formed for walking rather 



