WORMS. 



185 



or nephrostome, into the ccelom, while at the other end 

 it empties to the exterior. Usually the tube is much 

 coiled and is enveloped in a network of small blood- 

 vessels. The annelids are divisible into several groups 

 or subclasses, only two of which need mention here. 



SUBCLASS I. CHLETOPODA. 



In these the body -cavities (ccelomic pouches) are well 

 marked, as in the earthworm, and each segment of the 

 body bears small bristles (chceta or seta?) which serve as 

 locomotor organs. Usually the rings visible upon the 

 external surface correspond to the somites. 



ORDER I. 



In these the chsetae are numerous in each segment and 

 are usually borne on fleshy outgrowths (parapodia) from 

 the sides of the body, which in 

 many forms efficient swimming 

 organs. The head (fig. 29) bears 

 fleshy feelers, or tentacles, and 

 eyes are commonly present. The 

 Polychsetes, of which there are 

 numerous species, are almost 

 entirely marine. For conven- 

 ience they may be divided into _ 



tWO groups. Ill the ERRAXTIA FIG. 29. Head and anterior 



i /, i n r somites of clam-worm Ne- 



the animal IS tltted lOr a tree reis), an example of an errant 



life and frequently the mouth 



is provided with strong jaws, making them to the associated 

 life terrible animals of prey. The other group, the TUBI- 

 COLA or SEDENTARIA, live permanently in burrows from 

 which the head, often furnished with numerous tentacles 

 and gills, can be protruded. In life the tentacles are in 



