XII] 



ASTACUS 



183 



develop sharp cutting edges on the basal segments and to diminish 

 the size of the distal segments. The cutting edges are termed 

 gnathobases. This change becomes more and more marked as we 

 proceed forwards. Thus in the second maxillipede the distal joints 

 are reduced to three (the finger being absent) and the ischiopodite 

 is as long as all three put together and finally in the first maxillipede 

 the basipodite and coxopodite are greatly enlarged and produced 



FIG. 72. Left mouth appendages of Astacusftuviatilis, slightly magnified. 

 The other appendages are shown in Fig. 73. 



I. Mandible. II. First maxilla. III. Second maxilla (Scaphognathite). 

 IV. First maxilliped. V. Second maxilliped. VI. Third maxilliped. 

 en. Endopodite. ex. Exopodite. ep. Epipodite. ex & ep. Scapho- 

 gnathite, i.e. enlarged exopodite which in III forms a scoop for circulating 

 water over the gills. 



into cutting edges (gnathobases) and the whole endopodite is reduced 

 to two tiny segments, which, taken together, are not as long as the 

 basipodite. 



A remarkable feature about the maxillipedes is that they each 

 possess a well developed exopodite in the form of a whip-like filament 



