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. 



Fig. 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"), 



