XI 



PHYLUM ARTHROPODA 



543 



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

 in huge claws or cliche- , and hence called cliclipcds (Fig. 4'30, 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. 43 1, 5-7}. 



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

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



enJ- 



en 3 



5. 2". d Maxilla 6. if Maxilliped 



7. 3 r . d Maxilliped 



8. 3 r . d Leg 



erv- 



-Jjr.-t 



Organs lO.Swimming Poor 



ex. 



-fir 2 

 -in 

 ll.Uropod 



FIG. 431. Typical appendages of Astacus. en. 1 . r >, podomeres of endopodite ; <-p. epipodite ; 

 ex. exopodite ; rt. ttagella ; <i. gill ; })/-. 1, pr. 2, podomeres of protopodite ; 1 3, podomeres of 

 axis of antennule. (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 (y) attached to it. Obviously 

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



