VARIOUS 



251 



forms often encrust stones in large sheets. They are 

 strangely degenerate animals, for they begin life as free- 

 swimming, tadpole-like larvae, which approach some- 

 what to the Vertebrates in their structure. 



u. 177. SERPULA, A TUBE-DWELLING 

 BRISTLE-WORM. (FROM THE "CAM- 

 BRIDGE NATURAL HISTORY," BY PER- 

 MISSION OF MESSRS. MACMILLAN.) 



FIG. 178. AMPHI- 

 NOME, A BRISTLE- 

 WORM ("BLAKE"). 



