ALLIES OF THE EARTHWORM 



223 



they leave their burrows to swim at the surface. It is likely, 

 however, that in most cases they do not withdraw the entire 

 body from the burrow, but reach out in all directions for prey 

 that comes near them. When driven from their burrows in 

 the daytime they swim away, and at that time look very 

 beautiful, as the couplet above suggests. Nereis has two 

 horny jaws, sharp- 

 pointed, and bend- 

 ing to meet at the 

 tips. The jaws are 

 concealed by the 

 infolded pharynx 

 when not in use. 

 When about to 

 seize its prey, which 

 consists chiefly of 

 small, live sea-ani- 

 mals, the sandworm 

 suddenly everts the 

 pharynx, and the 

 jaws, thus freed, at 

 once spread hori- 

 zontally and seize 

 the victim. 



Comparison of 

 the external appear- 

 ance of the sand- 

 worm with that of 

 the earthworm brings out some points of difference, as well 

 as some points of similarity. We observe the same division 

 into somites of approximately uniform structure throughout 

 the body. Fully developed locomotor organs, and a distinct 

 head with eyes and tactile sense-organs, serve to adapt Nereis 

 to the necessities of its environment. 



EIG. 108. Photograph of Tube- Worm. Slightly 



reduced 

 1, thread-like gills; 2, tentacles 



