196 BULLETIN OF THE 
broken by an eccentric protuberance on one side. Both mouth and anus open 
through the lower hemisphere ; the former on one side just below the upper of 
the equatorial ciliated bands, and the latter on the eccentric prominence already 
mentioned. The whole exterior surface of the body is ciliated, and the equa- 
torial band consists of two parallel rings, which extend side by side for most of 
their course, and separate from each other in the region of the mouth, the 
larger passing above and the smaller below this orifice. This position of the 
two ciliated rings in an older larva can be seen in Loven’s original figures of 
the European larva, The upper hemisphere has its walls unbroken by any ori- 
fice, and is of regular dome-like shape. At its pole arises a short flagellum (f), 
which waves back and forth as the larva moves through the water. The flagel- 
lum found at its apex is an embryonic structure, and appears to be lost in 
more advanced larve. On the body walls just below the pole, in a granular 
zone surrounding the point from which the flagellum arises, there is a collection 
of cells more or less scattered, the thickness of which decreases more and more 
near the ciliated equatorial band. This granular mass is the first appearance of 
that nervous centre which later aggregates about this pole of the larva, and 
bears the ocelli. Slightly removed from the base of the flagellum, in the walls 
of the larva, are two pigment spots, one on each side, with well-marked lens, 
which as the larva grows older and older approximate closer and closer, until 
they are brought into the immediate vicinity of the pole, in connection with 
the consolidated collection of cells already mentioned. In the youngest larva, 
however, they are widely separated ; later, they grow nearer each other. Two 
prominent clusters of cells (¢ d) are found in the lower hemisphere in the walls 
diametrically opposite the cluster on the upper hemisphere. These also later 
form a nervous centre at this extremity of the worm. Around the rim of the 
larva, in the slight ring-shaped protuberance from which the cilia arise, many 
brown and yellow colored cellular bodies (Fig. 10°, p) of a problematical char- 
acter can be found. These bodies vary somewhat in color and size, being gen- 
erally brownish, yellowish, or greenish, and have a regular spherical shape. 
They appearto be suspended in membranous dilatations of the disk rim, and 
to hang from it by a slight attachment. Their disposition on the bell margin 
is irregular, and not constant. Can this be an instance of the symbiosis of an 
algous growth on a worm larva? 
The interior of the larva is occupied for the most part by three cavities, each 
with its own walls separate from those of the body cavity. Two of these have 
external openings into the medium in which the larva lives. The greater part 
of the interior of the larva is occupied by the largest of these three organs, 
which is called the stomach. This structure, which is almost globular in 
shape, has two openings, one into each of the two smaller cavities. It does not 
communicate with the surrounding water, and its whole inner surface is cili- 
ated, Of the remaining two internal sacs, one is an esophagus, and the other 
an intestine. The cesophagus opens externally through the mouth, and inter- 
nally into the stomach. Its walls are muscular, contractile, and the inner 
surface is ciliated. Granules of food in masses were observed in its cavity. 
