COE: TERRESTRIAL NEMERTEAN OF BERMUDA. 
559 
with a sensory epithelium to form the highly specialized frontal 
organ of the adult (fig. A, p. 540). 
Alimentary canal .— When the body of the young embryo begins 
to elongate, the blastopore and, to all appearances, the whole lumen 
of the primitive alimentary canal become obliterated. The whole 
interior of the body is then occupied by a mass of large vacuolated 
endodermic cells, this mass filling practically the entire space 
enclosed by the body walls as far forward* as the brain (pi. 24, 
fig. 12). 
In most individuals no lumen whatever is to be found within this 
mass of cells until a comparatively late period in the embryonic 
development, when the body has become decidedly worm-like in 
shape. A splitting then occurs which gives rise to a conspicuous 
lumen passing through the midst of the cell mass. This lumen 
forms the cavity of the intestine proper and the intestinal caecum 
of the adult. It extends throughout the length of the endodermic 
mass, from near the brain region to the posterior end of the body. 
Whether this splitting takes place along a line corresponding to 
the earlier position of the primitive alimentary canal is uncertain, 
this canal having been so completely obliterated at a much earlier 
period. 
In the meantime an invagination at the anterior end of the embryo 
gives rise to the rhynchodaeum. This invagination grows posteriorly 
as a rather narrow canal nearly to the brain, where it swells out into 
a conspicuous chamber (pi. 24, figs. 10, 13). From this chamber 
two limbs grow out, of which one passes directly backward 
between the brain lobes and dorsal to the commissure and con¬ 
tinues posteriorly to form the lining of the proboscis (pi. 21, figs. 
11, 13). The other limb bends sharply ventrally and passes on the 
ventral side of the brain commissure as a narrow tube, the esoph¬ 
agus, which enlarges immediately behind the brain into an oval 
chamber of considerable size, the stomach. 
Both rhynchodaeum and esophagus are at this time lined with 
rather small columnar cells, while the stomach has very large, highly 
columnar cells, a portion of which are covered with long and con¬ 
spicuous cilia, while others are converted into gland cells (pi. 24, 
figs. 12, 13). 
The stomach remains for some time as an oval chamber im¬ 
bedded in the anterior portion of the endodermic mass immedi- 
