than the exopodite, is made up of the following five successive pieces, (1) a short 

 ischiopodite, which is immovably united with the basipodite, (2) a long meropodite, 

 (3) a short carpopodite, (4) a short and broad piroi^odite, and (5) a semioval 

 dadylopodite. The slender exopodite resembles that of the 1st maxillipeds. 



The third pair of thoracic appendages are the third or external maxillipeds : 

 they are foot-jaws in which the resemblance to the ordinary appendages of the 

 thorax is more decided than in the case of the other maxillipeds. Except that 

 their endopodite is longer and their exopodite shorter, and that their ischiopodite 

 is longer and their meropodite relatively shorter, and that their podobranch is a 

 functional gill-plume, they do not essentially differ from the 2nd maxilhpeds. 

 The inner edge of their ischiopodite is, however, furnished with an elegant row 

 of calcareous teeth. 



The fourth to the eighth pairs of thoracic appendages, which are commonly 

 known as " legs," are modified for locomotion and, in part, for prehension, and 

 though they are not all exactly alike, have all an essential similarity of structure. 

 None of them have an exopodite, and in all of them the endopodite consists of 

 five subcylindrical segments, or joints— ischiopodite, meropodite, carpopodite, 

 propodite, and dactylopodite — which form, in succession, a continuous series with 

 the coxopodite and basipodite, all of these joints being capable of independent 

 motion, except the basipodite and ischiopodite which are firmly united and move 

 as a single piece. All of these appendages except the last have, articulated to 

 the dorsal angle of the coxopodite, an epipodite and a podobranch. 



The fourth pair, which are known as the great chelipedfi, are much the 

 longest and vastly the most massive of the appendages of the thorax : their 

 propodite is of enormous size and has its distal angle produced far beyond the 

 articulation of the dactylopodite as a long process, which is a counterpart of 

 the dactylopodite itself and forms with the dactylopodite a pair of strong 

 pincers — the chelae. 



The fifth and sixth pairs are slender and subcylindrical : they also end in 

 chelae, which are small. 



The seventh and eighth pairs are simple legs for crawling, the seventh are 

 a little longer than, and the eighth are about the same length as, the fifth and 

 sixth pairs. 



5. Of the Segments and Appendages of the Abdomen. 



The typical abdominal segment, and its appendages, have already been 

 described. The segments are all freely movable : the tergum of the first seg- 

 ment is overlapped by the carapace and overlaps the tergum of the second, the 

 tergum of the second is overlapped by that of the first and overlaps that of 

 the third, and so on in succession. 



The first abdominal somite differs from the others in the large extent of 



