The Lobster. 79 



abdominal segment and, if possible, give a reason for the 

 same. 



Is there anything to show that the last cephalothoracic 

 appendage is homologous with the abdominal appendages? 

 The latter have been called pleopoda. If the homology 

 can be shown for the last, it must also be claimed for the 

 remaining cephalothoracic appendages of equivalent origin 

 and structure. How many such appendages are there? 

 (Answer the question by comparing points of origin, num- 

 ber of joints, position of sensitive hairs, and number and 

 position of protective spines. It will probably be concluded 

 that there are five pairs closely resembling each other.) Why 

 the remarkable enlargement of the anterior pair, t\\Q forceps? 

 Do the five pairs of appendages arise from five segments? 

 Will you admit of the " Rule of Savigny " : "A pair of ap- 

 pendages represents a segment, though segments may occur 

 without appendages"? How many segments, then, are there 

 from the posterior end of the body to the forceps ? 



The appendages lying immediately anterior to the forceps 

 are more or less specialized. They may be pressed down 

 one after the other, like leaves of a book, and if found 

 homologous with the appendages already examined, their 

 number will indicate the number of supporting segments. 



The most posterior, the third maxilliped, is in pa~t like one 

 of the ambulatory appendages already studied. Examine 

 its point of origin, count its joints, etc. The immediately 

 anterior, second maxilliped. is not remarkably different from 

 the third, though \hefirst maxilliped is considerably altered. 



The line separating the maxillipeds from the anteriorly- 

 lying second maxillce divides the head from the thorax. 

 There are two pairs of maxillae, the second, broad and leai- 

 like ; the first, smaller and tricleft. 



