136 Papers from the Department of Marine Biology. 
The gut is markedly compressed dorso-ventrally. There is no defi- 
nite division into cesophagus, stomach, and intestine, although its 
much greater size in the central region indicates the probable location 
of the stomach. At the anterior end the tube tapers more gradually 
than at the posterior, where it retains a tendency to curve somewhat 
toward the ventral surface of the embryo. The gut is lined with a 
Fic. 18.—Transverse sec- 
tion taken somewhat pos- 
terior to that represented 
in fig. 17, showing first 
and fourth tentacles cut 
through their anterior 
part, and lobes two and 
three through their pos- 
terior. a.e., anterior en- 
teroccele; g, gut; h, hydro- 
coele; 1’, lumen of lobe 3 
of hydroccele; m, mesen- 
tery-like strand of tissue 
connecting the stomach 
with the wall of the em- 
bryo; sp., spine; @, @. &, 
@, tentacles 1, 2, 3, 4. 
X 233. 
Fic. 19.—Transverse sec- 
tion through posterior 
part of embryo. a.e., an- 
terior enteroccele; g, gut; 
, lumen of lobe 5 of hy- 
droccele; p.e., posterior 
enterocceele; sp., spine; 
, tentacle 5. 
single layer of cylindrical cells with clear cytoplasm and centrally 
located nuclei. The lumen is entirely closed and there is no indication 
of communication with the exterior. 
Anterior to the stomach, and bending down over it, lies the undivided 
anterior enteroccele. It is composed of an exceedingly thin layer of 
cells which lies flatly pressed against the adjacent tissues, except where 
