VOL. It. ] Balanogtossus. 189 
The abdomen is several times longer than the other two parts 
combined and is very distensible. It is soft and frail and one rarely 
sees it whole, so easily does it break as the animal is being extracted 
from its tube in the soft mud or sand in which it lives. 
The surface of this region is much less regular than that of the 
other two parts previously described, it being, particularly in its an- 
terior, pharnygeal portion, somewhat quadrilateral with irregular 
transverse folds affecting particularly the dorsal angles. As seen by 
the figure the gills, gz., arearranged in a double series on the dorsal 
side of the animal,.each series, as seen from the surface, being 
composed of a large number of crescentic openings. 
The sexual orifices are also found in this region, but are very 
minute, s. ov. The three portions of the animal differ from one 
another in color. The proboscis is a uniform very light yellow, the 
collar is also yellow but of a considerably more pronounced shade. 
The abdomen is of a brownish tint marked with darker spots, and 
for a portion of its length has a greenish shade from the presence of 
the liver within showing through the body wall. In size the crea- 
ture may reach a length of eight inches in some of the larger species. 
It will be noticed from this description that the animal is entirely 
without paired appendages, either for locomotion, prehension, or 
sensation. Its only organ of movement is its proboscis. 
The animal is entirely marine, so far as known, and is confined to 
shallow water near shore, and as already said, lives buried in mud 
or sand. ©The species found on the New England coast can be col- 
lected at low tide only, when the earth in which it lives is uncovered. 
It is usually found about a foot or two below the surface, and one 
readily determines where to dig for it by the very characteristic 
spirally coiled cast of sand and mud at the opening of its tube that 
has been ejected by the animal within. 
As it is in the creature’s role as a candidate for a place among 
the chordata that it has become chiefly distinguished in recent years, © 
the attention that we here give to its anatomy may profitably be 
from the standpoint of a comparison with the fundamental chordate 
structure. In this way the points of agreement may be brought 
out with emphasis, and at the same time the points of disagreement 
may be made equally emphatic. 
Bateson, who, as already said, was the first to carry out this com- 
parison in detail, points out three primary and four secondary par- 
