ECHINODERMA. 



127 



performing at the 

 same time the of- 

 fice of absorbents 

 and conveying the 

 chyle to the great 

 intestinal vein (^), 

 from which pro- 

 ceed the singular 

 and beautiful re- 

 spiratory plexuses 

 (h, h), which are 

 submitted to the 

 influence of the sea 

 water by contact 

 with the branchial 

 trees. 



The aerated blood 

 is conveyed to a 

 great mesenteric 

 trunk (i, i), or 

 branchial vein, 

 from which it is 

 transmitted to the 

 parietes of the 

 body, and returns 

 by the cloaca to 

 form the intestinal 

 artery. 



Hunter has fi- 

 gured certain glan- 

 dular sacs opening 

 into the stem of 

 the hollow branch- 

 iae, which may be 

 regarded as a ru- 

 dimental form of 

 an excretory or 

 renal system. 

 The chief divisions of the nervous system consist of the pharyngeal 

 ring, which is closely applied against the inner side of the calcareous 

 circle, and of the flattened chords which proceed along the groove 

 or middle interspace in each of the pairs of longitudinal muscles, which 

 traverse the interior of the integument of the animal through its entire 



