138 



Papers from the Department oj 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 



V t 2 

 ;K.xt- 



*, iftl -S ' y. i 



p.c. 



FIG. 21. Sagittal section 

 to left of embryo, through 

 two vesicles of left pos- 

 terior enterocoele. Pore 

 canal is seen near first 

 primary tentacle, just as 

 it is given off from the 

 ring of the hydrocoele. 

 a.e., anterior enteroccele; 

 Q, gut; I 1 , P, lumen of lobes 

 1,2 of the hydroccele ;p.c., 

 pore canal; p.e., left pos- 

 terior enteroccele; sp., 

 spine; t 1 , t-, tentacles 1, 2. 

 X 233. 



21 



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 



