CHAPTER VIII 



THE ANATOMY AND PHYSIOLOGY OF 

 CRUSTACEA: THE LOBSTER 



General Form of the Lobster. — The lobster closely 

 resembles the crayfish (Fig. 123) except it i.s much larger. 

 Like the cockroach it is approximately bilaterally .S3'mmetrical 

 and is segmented. We may distinguish in the bodj' the trunk 

 and the appendages. The trunk is cUxided into two main 

 regions : the abdomen and a united head and thorax (cephalo- 

 thorax). The segments of the abdomen are distinct like those 

 of the cricket, but unlike the latter each segment bears a pair 

 of a]Dpendages. There are seven segments in the abdomen of 

 the lobster. Since the segments of the cephalothorax are not 

 chstinct, they cannot be counted directly, ))ut by assuming that 

 each pair of appendages corresponds to a segment, as in the 

 case of the abdomen, the number of cephalothoracic segments 

 is estimated to be thirteen. 



The appenrlages of the body show a di^-ersity of form in 

 accordance with the various kinds of work they have to do. 

 At the front of the head are the two pairs of long organs of 

 touch — antennae; then come the stout crushing jaws (mandi- 

 bles) ; next are five pairs of appendages concerned in holding the 

 food while it is being devoured. Then follow five pairs of walking 

 appendages and, on the abdomen, a number of pairs of flappers 

 (swimmercts), the series terminating in the great tail flappers. 

 As can be inferred from the structure of the appendages the 

 lobster can both walk over the rocks at the edge of the sea or 



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