200 BULLETIN OF THE 
into a clear space beneath the ventral surface, the beginning of the cesophagus. 
No ciliary ring has yet appeared at the anal end of the larva. 
The embryo, although possessing spines which can be projected from the 
body, and a ring of cilia about the head, is still with others enclosed in the 
mass of slime in which they were laid. All have very limited movements, 
even when artificially set free from the cluster in which they are bound 
together. Their bodies, especially the central part, have a dirty green color, 
while the head, ciliated band, and body walls are more transparent. 
In the subsequent changes which the external form of the larva passes 
through, there is little of interest to be mentioned. Parapodium after parapo- 
dium is added, increasing the length of the body of the worm. The new seg- 
ments always arise back of that which is previously formed, while in advance 
of all, between the first body segment and the posterior border of the ciliated 
band, marked on the sides by the lateral rows of pigment spots, there are no 
lateral appendages to the external body walls. From its position and its sub- 
sequent history, this bare part of the body immediately behind the head is 
probably homologous with the anterior body region (a7, Fig. 1), which has 
been already elsewhere described in the genus Prionospio. 
In my figure of the larval Lumbriconereis with two pairs of well-formed 
spines, it will be noticed that the digestive tract has already differentiated itself 
into two regions, an anterior, larger, and more capacious, and a posterior more 
tubular portion. The former of these is later changed into the stomach, while 
the latter is destined to form the intestine. The point of separation of one of 
these from the other is not yet well marked. 
At the anterior end of the stomach, on one side, a globular body is constricted 
from the stomach walls at about this time. The ultimate history of this organ 
has not been traced, and its function is unknown. A similar body has been 
mentioned in the young Nephthys. The jaws in the larval, as in the adult 
Lumbriconereis, are very complicated, and consist of two parts, a dorsal and a 
ventral. The ventral jaw is formed of a single crescentic chetinous plate, the 
horns of which extend forward. The regularity of the concavity of the ante- 
rior edge of the jaw is broken by a single small median tooth. The posterior 
edge of the jaw is continued backward into two elongated projections, which 
extend parallel with each other, and are separated by a narrow slit. 
The dorsal jaws are still more complicated than the ventral. They consist 
of four pairs of chetinous articulations which act as teeth, and are arranged in 
pairs the members of which are placed opposite each other. The two anterior 
of these are simple teeth with smooth edges, the former with a triangular out- 
line ; the latter is more elongated, narrower, and more pointed. 
The body of the dorsal jaws is formed of two flat or slightly curved oblong 
plates, whose opposite edges are serrated. By the approximation of these bor- 
ders, the true function of this complicated mechanism is accomplished. To 
these oblong, serrated plates, on their posterior border, are articulated the last 
pair of bodies which form the dorsal jaws. These take a triangular shape, and 
have for their function a firm attachment for the remaining parts of the jaw. 
