268 



COMPARATIVE ZOOLOGY. 



fringed "arm," generally coiled up, and supported by a 

 calcareous framework. The animal, having no gills, re- 

 spires by the arms and the mantle. Brachiopods were 

 once very abundant, over two thousand extinct species 

 having been described ; but less than a hundred species 

 are now living. 137 They are all marine, and fixed; but of 

 all Worms, they enjoy the greatest range of climate and 

 depth. 



Class VI. — Annelides. 

 The Annelides include the highest and most specialized 

 Worms. They have many segments, spines or suckers 

 for locomotion, a supercesophageal brain, a ventral chain 



Fig. 223.— Marine Worm (Cirratulus grandis), with extended cirri. Atlantic. 



of ganglia, and a closed blood-system. There are three 

 main divisions: the flattened Leeches, without definite 

 segments or bristles, and with suckers for locomotion ; the 



