XI 



PHYLUM ARTHROPODA 



543 



walks : in front of these is a pair of very large le'gs terminating 

 in huge claws or chelce, and hence called clielipeds (Fig. 430, 9). 

 The three anterior segments bear much smaller appendages 

 more or less leg-like in form, but having their bases toothed to 

 serve as jaws : they are distinguished as maxillipeds or foot-jaws 

 (Fig. 431, 5-7). 



The structure of these appendages is best understood by a con- 

 sideration of tl^e third maxilliped (7). The main portion of the 



en,. 3 



5. a 1 ?* Maxilla 6. I^Maxilliped 



O.Copulatory Organs 



-fir.f 

 lO.SwimmingFool- 



ll.Uropc 



FIG. 431. Typical appendages of Astacus. tn. 15, podomeres of endopodite ; ep. epipodite ; 

 tx. exopodite ; d. flagella ; ft. gill ; pr. 1, pr. 2, podomeres of protopodite ; 1 3, podomeres of 

 axis of antemuile. (After Huxley.) 



limb is formed of seven podomeres arranged in a single series, 

 strongly calcined, and with the exception of the second and third, 

 which are fused mo vably articulated with one another. .The second 

 podomere, counting from the proximal end, bears a many-jointed 

 feeler-like organ (ex), and from the first springs a thin folded 

 plate (ep) having a plume-like gill (g) attached to it. Obviously 

 such an appendage is biramous, but with one of its branches 



