3S4 



ARTHROPODA 



leaping motion, whence the common name, lieach fleas. In swimming 

 tlie alidomen is ahernately bent against the lireast and then forcibly 

 straightened. 



The boiiy is usually strongly compressed from side to side. The 



anterior thoracic feet generally bear large 

 i-pimcral plates (iig. A}:-.), which e.\tend 

 the sides of the l.mdy down«-ards, while 

 on the inner side delicate gills or gill sacs 

 (lig. 410, /';•) arise from their bases. In 

 the female brood lamelke (brl) are added 

 wliich enclose a brood chamber beneath 

 the body in wliich eggs or young are car- 

 ried. The three anterior pairs of ab- 

 dominal feet are two-branched, richly 

 haired, and serve to create currents of 

 water wliich pass c^ver the gills. The 

 remaining alidominal feet, through bira- 

 mous, are shorter 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 persists. 



Sub Order I. ITATERIXA. Large head and eves; strong prchcnsil'^ feet. 

 Live attached to other pekiLjic animals on which they feed; Hypcn'a,''' Plironima.* 

 Sub Order II. GA^SOIARINA. Head much smaller; alidomen well developed ; 

 mostlv free swimmers. Numerous species in the sea. Canimanis''* in shallow 

 water, some fluviatile; Orclicslia''' above tide marks. Clnliira icri.briiiis* 



Fig. 410, — Crrs5-section 

 Ampliipode"('r()/)///f(;)/, (froni Lang, 

 after Delage'). bf. thoracic leg; 

 bm, ventral nerve conl: /ir, 

 branch'ue; I'rl, brood lamella; 1/, 

 intestine; /;. heart; /, liver; ov, eggs 

 in brood chamber. 



Fig. 411. — Gammanis oriialus* d'rom Smiths 



destroys submerged wood. Sub Order III. L.-EIMODILOD \, Larasilic or 

 semi-jjarasitie; second thoracic somite is fused to head; a]>peiMlages lacking 

 from some thoracic segments, abdomen reduced. CaprcUa;''- on hydroids. 

 Cyamus ccti, parasitic on whales. 



