294 



COMPARATIVE ANATOMY 



CHAP. 



Order 2. Isopoda. 

 Body broad, often flattened dorso-ventrally. Only the foremost thoracic seg- 

 ment is fused with the head, the other 7 are free. Ko freely projecting shell fold. 



-srrh 



Fig. 197.— Organisation of Orohestiacavlmana, male (after Nebeski). c+I,Head+lst thoracic 

 segment ; II-VIII, free thoracic segments with their extremities ; Pi-pj, atidominal segments ; tn, 

 anterior, og, posterior antenna ; a, eye ; ce, a:sophagus ; /./, foot-jaw ; br, gills ; Im, ventral chord ; 

 g, brain ; aoa, anterior aorta ; sm, cesophagal stomach ; vd, unpaired intestinal cfficum ; od, egg- 

 bearing part of the germ glands ; A, heart ; (, testis ; vs, vesica seminalis ; de, ductus ejaculatorius ; 

 ehd, entrance of the urinary gland (hd) into the intestine ; aop, posterior aorta ; I, ends of the 

 hepatic tubes ; e(?, posterior end of the intestine. 



The 2 pairs of maxillie without feelers. Abdomen generally short, often reduced, 

 mostly consisting of 6 segments with biramose lamellated pleopoda, whose branches, 

 especially the endopodites, function as gills. Heart in the abdomen, generally 

 stretches as far as into the posterior thoracic region, with 1 to 2 pairs of ostia. 



