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 
their glistening hairs brings the food 
to the mouth, which is situated immedi¬ 
ately beneath. The head-lobe is blended with 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 
Chcetopterus. 
