\l 



PHYLUM ARTHROPOD A 



543 



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

 in h.nge claws or chelce, and hence called ckelipeds (Fig. 4.S0, 9). 

 The three anterior segments bear much smaller appendages 

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

 serve as jaws: they are distinguished as ttujjjjlijwls or foot- jaw s 



(Fig. 4;n,£-7). 



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

 sideration of the third maxiiliped (7). The main portion of the 



5. 2^Maxilla 6. P f Maxiiliped 



7. 3 r . d Maxiiliped 



8. y." Leg 



pr.t 



O.Copula^ry Organs lO.SwimmingFoor 



-bri 

 ll.Uropod 



Fig. 431.— Typical appendages of Astacus. en. 1 — ~>, podonieres of endopodite ; ep. epipodite ; 

 ex. exopodite ; jt. flagella ; a. gill ; p>: 1, %n: t, podonieres of protopodite ; 1—3, podonieres of 

 axis of antennule. (After Huxley.) 



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

 strongly calcined, 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 (<j) attached to it. Obviously 

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



