138 Papers from the Department of Marine Biology. 
developed primary tentacles. In this stage these are spherical or 
slightly elongated structures which take up the stain and retain it 
much more tenaciously than do any of the other tissues. The small, 
round lumen lies well to the dorsal side, where the wall is composed of 
a single layer of cells. 
The fifth lobe of the hydroccele is the most posterior, and lies directed 
downward opposite the posterior end of the stomach (fig. 20). The 
second and third are the most anterior, and lie side by side near the 
anterior termination of the gut. They are directed anteriorly and 
somewhat laterally. Figure 17 shows a transverse section passing 
through the two corresponding tentacles, and consequently gives a 
Fig. 21.—Sagittal section 
to left of embryo, through 
two vesicles of left pos- 
- terior enteroccele. Pore 
canal is seen near first 
primary tentacle, just as 
it is given off from the 
ring of the hydroccele. 
a.e., anterior enteroccele; 
g, gut; /!, 2, lumen of lobes 
1, 2 of the hydroceele; p.c., 
pore canal; p.e., left pos- 
terior enteroceele; sp., 
spine; @, ¢, tentacles 1, 2. 
ERE 
slightly oblique section of the lumen. The fourth lies on the right side 
of the embryo between lobes 3 and 5, and is directed laterally and some- 
what posteriorly. The first is situated opposite it on the left side of 
the median line. Figure 18 shows a transverse section through the 
embryo at such a level as to cut through the anterior portion of the 
first and fourth tentacles and the posterior part of the second and third. 
The pore canal is given off from the hydroccele ring between lobes 1 
and 2. It passes dorsally toward the wall of the stomach, where it 
turns to the left and, circling around that organ, takes a course at first 
directed posteriorly and then dorsally until it reaches the aboral wall 
of the embryo, where it opens upon the exterior. The pore canal is 
