364 THE CRAYFISH CHAP, vn 



head, the five pairs of legs springing from the thorax 

 and the little fin-like bodies arising from the sterna o 

 the abdomen. It will be convenient to begin with the 

 last-named region. 



The third, fourth and fifth segments of the abdomen 

 bear each a pair of small appendages, the swimming 

 feet or pleopods (Fig. 90, P, N, X). A pleopod (Fig. <)i 

 10) consists of an axis or protopodite having a very shor 

 proximal (pr. i) and a long distal (pr. 2} podonicrr, aiu 

 bearing at its free end two jointed plates, fringed with 

 setae, the endopodite (en) and ffxopodite (ex) . These appen 

 dages act as fins, moving backwards and forwards with 

 a regular swing, and probably aiding in the animal's 

 forward movements. 



In the female a similar appendage is borne on tin 

 second abdominal segment, while that of the first i 

 more or less vestigial (p. 159). In the male the first am 

 second pleopods (Fig. 91, 9) are modified to form in 

 complete tubes which serve to transfer the spermato 

 phores (p. 382) to the body of the female. The sixth 

 pair of pleopods (n) are alike in the two sexes: they 

 are very large, both endopodite and exopodite having 

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

 the parts they lie one on either side of the telson, form 

 ing 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 fou 

 posterior segments bear long, slender, jointed legs (8) 

 with which the animal walks : in front of these is ;i pai 

 of very large legs terminating in huge claws or chela* 

 and hence called chelipeds (Fig. 93, bf. 4). The thive 

 anterior thoracic segments bear much smaller appen 

 dages, more or less leg-like in form, but serving as jaws 

 they are distinguished as maxillipeds or foot-jaws. 



