PHYLUM ARTHROPODA 



543 



walks : in front of these is a pair of very large legs terminating 

 in huge claws or diehr, and hence called chdipcds (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 ma^iillipeds or foot-iaws 

 (Fig. 431, 5-7). 



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

 sideration of the third ma.iilli'ped (7). The main portion of the 



O.Copulatory Organs 



-pr.-f 

 10. Swimming Fool* 



11. U r o p o d 



Fig. 431. — Typical appendaj^es of Astacus. en. 1 — .5, podomeres of endopodite ; ep. epipodite ; 

 t^x. exo23odite ; Jl. flagella ; g. gill ; pr. 1, pr, ',', podomeres of protopodite ; i — ■?, podomeres uf 

 axis of anteilnule. (After Huxley. ) 



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

 strongly calcified, and — with the exception of the second and third, 

 which are fused — movably 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 



