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 superoesophageal brain, a ventral chain 



Fio. 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 



