294 



GOMPAEA TIVE ANA TOMY 



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. No freely projecting shell fold. 



& 



WGT\\, Vr ** ed 



a & 



J r 



FIG. 19". Organisation of Orchestia cavlmana, male (after Nebeski). c+I, Head+ 1st thoracic 

 segment; II-VIII, free thoracic segments with their extremities; PI-PJ, abdominal segments; j, 

 anterior, o, posterior antenna ; a, eye ; K, oesophagus ; kf, foot-jaw ; br, gills ; Im, ventral chord ; 

 g, brain ; aoa, anterior aorta ; sm, cesophagal stomach ; iul, unpaired intestinal crecuni ; od, egg- 

 bearing part of the germ glands ; h, heart ; t, 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 ; ed, posterior end of the intestine. 



The 2 pairs of niaxilloe 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. 



