6 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
distal surface. These fibers, like those of the muscle ring from which 
they come, are cross striated in appearance. In addition, transverse 
fibers connecting these two lobes of the foot pass near the surface 
from one to the other. The median lobe of the foot is furnished with 
two small lateral muscles, one on either side. These arise near the 
circular muscle and pass down the foot to near the tip. The principal 
muscle of the parapodia consists of apparently unstriated fibers which 
extend from one fin over into the other. These fibers, which pass 
through the neck dorsal to the ventral longitudinal muscles, probably 
serve to retract the parapodia. Each fin is also supplied with other 
fibers attached on either side of its base. These latter fibers evidently 
function in connection with the flapping of the parapodia. 
There are four other pairs of muscles in the head, all in front of the 
cephalic band of cilia. Of these, the two long tentacular retractors 
start one on either side near the anterior end of the lateral longitudinal 
muscle and extend up into the tentacles. Just dorsal to the origin of 
each of these, another muscle takes its rise and extends about to the 
base of the corresponding tentacle. Still nearer the median dorsal 
line a third muscle runs from the level of the first ciliated band to the 
edge of the hood between the tentacles. The fibers of this pair of 
muscles, like those of the two preceding pairs are cross striated in 
appearance. The remaining pair of anterior muscles is in front, 
extending from a point medial to the anterior lobes of the foot forward 
to the ventral edge of the hood. The last three pairs by their contrac- 
tion apparently tend to draw the hood back, thus enlarging its mouth 
when the buccal mass is to be protruded. 
In addition to these somewhat specialized muscle fibers there are 
in the walls of the head a great many other fibers running practically 
parallel to the cephalic ciliated ring. Rather curiously they all show 
the cross-striated condition. The anterior circular muscle mentioned 
above is merely a thickened aggregate of these fibers. Back of the 
attachment of the parapodia are still other cross-striated fibers running 
through the body and forming a kind of diaphragm between the 
ganglia in front and the stomach behind. 
• The Digestive System. 
The digestive organs are shown in their relative position in figure 6 
(pi. 2, the ruled portions). In most of the specimens examined the 
