I. CRUSTACEA: AMPIIIPODA. 



4;j9 



beach fleas. In swimming the abdomen is alternately bent against 

 the breast and then forcibly straightened. 



The body is usually strongly compressed from side to side. 

 The thoracic feet generally bear large epineural plates (fig. 433), 

 which extend the sides of the body 

 downward, while on the inner side 

 delicate gills or gill sacs (fig. 449, 

 hr) arise from their bases. In the 

 female brood lamellas (f^i'l) are 

 added — In'oad chitinous plates 

 which enclose a brood chamber 

 beneath the body in which eggs or 

 young are carried. Tlie three an- 

 terior pairs of abdominal feet are 

 two-branched, richly haired, and 



serve to create currents of water Fio. 44a.— Cross-section of Amphipod 



(Cnroimiunt). (trora nang, after I>i'- 



Which pass forward over the gills. lage.) /)/, thoracic lei;; hm, ventral 



■^ . . . *- nerve cord: fir, branchice; hrl, brood 



riie remaining thoracic feet, .lameUa; </, intestine; ;i, heart; !, liver; 



tn\ cKy:s In brood chamber. 



though biranioiis, are short and 



stout and form springing organs. The position of the gills 

 explains why the abdominal part of the heart is degenerate and 

 only the anterior thoracic portion with three pairs of ostia picrsists. 



Sub Order I. IIYPEPJNA. Large head and eyes; strong prehensile feet. 

 Live attached to olher peLigic animals on whieli they feed, llyperia. 

 vKiJiisanim * lives on the jelly fish Cyaiiea; Phrorihna,* warniei' seas. 



Riib Order II. GAMMARINA. Head much smaller; abdomen well devel- 

 oped; are mostly free swimmers. Numerous speeies in the sea. Gaiii- 



Flg. i')0. — Gaintiiarus Qrnatns* (From Sniith.) 



mams* occurs in shallow water, some being fluviatile; Orchestia* above 



tide marks. Chelura terebratis * destroys piles and other submerged wood. 



Sub Order III. L^'EMODIPODA. Parasitic or semi-parasitic forms in 



which the first (second) somite is fused to the head; appendages are lacking 



