WORMS 185 
which the tube is closed when the worm has withdrawn itself 
inside. The tubes are commonly found attached to shells and 
rocks, usually solitary, but sometimes in clusters, crossing and 
recrossing each other on the surface of the shell or rock. Plume- 
like gills are attached to the anterior end of the body. The color 
differs in different species. These worms may easily be mistaken 
for the mollusks Vermetus, which live in similar tubes of larger 
size, growing in masses. 
GENus Serpula 
S. dianthus. Tubes often three inches long and one eighth of an 
inch wide, the fixed end coiled and contorted, free end with circular 
opening; tubes often show circular ridges, marking periods of growth; 
operculum funnel-shaped, the exterior striated and the edge bordered 
with short processes; wreath of gills nearly circular and divided into 
two symmetrical parts; color variable. It is found in tide-pools, also 
on the under side of rocks at low-water mark, either solitary or congre- 
gated in masses, and ranges from Cape Cod to New Jersey. 
GEnus Spirorbis 
S. borealis. A minute calcareous tube, in a close, flat coil attached 
on one side; easily mistaken for a minute gasteropod shell; worm has 
an operculum and wreath of gills. Found on the fronds of seaweeds, 
on shells, etc. 
CLASS GEPHYREA 
This class of animals, once placed near the holothurians, be- 
longs with the annelid worms on account of their mode of devel- 
opment, their structure being entirely dissimilar. They are 
without segments and without parapodia. The body-cavity is 
filled with fluid and is traversed by connective tissue and fine 
muscular fibers. They are subcylindrical animals which can 
retract the anterior end of the body. The mouth is surrounded 
by tentacles, or by tentacular folds, and is at the base of the 
proboscis. They live in fissures of rocks, in sand, mud, rock, or 
coral, and in deep gasteropod shells. Their distribution is general. 
ORDER SIPUNCULOIDEA 
Genus Sipunculus 
S.nudus. The body is cylindrical, a foot or more in length when 
extended. It is divided into two portions. The anterior end, to the 
