ANNELIDS IN GENERAL 



249 



but also many other forms of varied structure. Some species are very- 

 large, one found in Java being said to attain a length of several feet with 

 a correspondingly great diameter. Some are able to climb trees. 



Among the fresh-water oligochaets are a large number of small and 

 relatively simple forms with not more than a pair of setae to each met- 

 amere, in some cases less. These are, in general, very transparent and 



Operculum 



Gills 



Fig. 156. — A colony of sabellid worms, Serpula vermicularis Linnaeus, showing the mass 

 of tubes and the expanded tentacles. {From Benham, "Cambridge Natural History,^' after 

 Cuvier, by the courtesy of The Macmillan Company.) The operculum closes the tube after 

 the worm has withdrawn into it. Natural size. 



without color, though sometimes, as in Aeolosoma, they contain brightly 

 colored oil globules scattered through the body. Some of them live in 

 aquatic vegetation, crawling about by movements of the setae combined 

 with the undulations of the body. Others live in tubes in the mud at 

 the bottom of ponds or other bodies of water, and frequently in colonies 

 containing large numbers of individuals. They extend themselves from 

 the mouth of these tubes, waving their bodies backward and forward, 

 but retreat into the tubes when strongly stimulated. A colony of such 

 worms in activity presents an animated appearance. 



