XXVII APPENDAGES 323 



protopodite having a very short proximal {pr. i), and a long 

 distal {pr. 2) podomere, and bearing at its free end two 

 jointed plates, fringed with setae, the endopodite {en) and 

 exopodite {ex). These appendages act as fins, moving back- 

 wards and forwards with a regular swing, and probably aid- 

 ing in the animal's forward movements. 



In the female a similar appendage is borne on the second 

 segment, while that of the first is more or less rudimentary. 

 In the male the first and second pleopods (9) are modified 

 into incomplete tubes which act as copulatory organs, serving 

 to transfer the spermatophores to the body of the female. 

 The sixth pair of pleopods (11) are alike in the two sexes : 

 they are very large, both endo- and exopodite having the 

 form of broad flat plates : in the natural position of the 

 parts they lie one on each side of the telson, forming with 

 it a large five-lobed tail fin : they are therefore conveniently 

 called uropods or tail-feet. The telson itself bears no 

 appendages. 



The thoracic appendages are very different. The four 

 posterior segments bear long slender, jointed legs (Pig. 81, 

 8), upon which the animal walks : in front of these is a pair 

 of very large legs terminating in huge claws or cheliz, and 

 hence called chelipeds. The three anterior segments bear 

 much smaller appendages (6, 7) more or less leg-like in 

 form, but having their bases toothed to serve as jaws : they 

 are distinguished as maxillipeds or foot-jaws. 



The structure of these appendages is best understood by 

 a consideration of the third maxilliped (Fig. 82, 7). The 

 main portion of the 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 



Y 2 



