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. No freely projecting shell fold. 



ctop 



--Ad 



.ed 



FIG. 197. Organisation of Orchestia cavimana, male (after Nebeski). c+ 1, Head+lst thoracic 

 segment; II-VIII, free thoracic segments with their extremities; Pi-p?, abdominal segments; cti, 

 anterior, a 2 , posterior antenna ; a, eye ; ce, oesophagus ; fc/, foot-jaw ; br, gills ; Im, ventral chord ; 

 g, brain ; aoa, anterior aorta ; sm, cesophagal stomach ; ltd, unpaired intestinal csecum ; od, egg- 

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

 elid, 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 maxillae 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. 



