ANNELIDS. 



437 



developed bristly parapodia, upon the upper side of each of which there is a 

 tongue-shaped gill. The head is remarkable in that the two large feelers blend 



TUBE-WORM (Hermella). 



into one and bear a few rows of broad, 

 flat bristles. They are thus converted 

 into a stopper, which closes the mouth 

 of the tube when the worm is retracted. 

 In Terebella, forming the family Tere- 

 bellidce, the tubes are formed of frag- 

 ments of sand or shell. 



In the family Serpulidce the gills 

 are restricted to the fore-part of the 

 body, and the water set in motion by 



Chcetopterus. their glistening hairs brings the food 



to the mouth, which is situated immedi- 

 ately beneath. The head-lobe is blended \yith the first segment, and not sharply 

 marked off from it, as in most of the worms hitherto described. These animals 

 live in calcareous (chalky) tubes, the apertures of each tube being closed when 

 the worm has retreated within by a tight-fitting stopper, formed from a modified 

 piece of one of the gills. The first tube made by the young worm is cylindrical 



