The Pluteus of Laganum sp. 



139 



evidently just in the process of formation at this stage, since in many 

 of the specimens it can be traced only a short distance from the hydro- 

 ccele ring and no external opening can be found. In some, however, 

 it maj- easily be followed throughout its entire length. No structure 

 corresponding to an ampulla is present. Figure 22 represents a sagittal 

 section taken through the left side of an embryo showing the external 

 termination of the pore-canal. In figure 21 its connection with the 

 hydroccele near the first lobe is represented. 



U 2 



'iPQI'i 



a**'S *" ' * :*8S3Pil 



FIG. 22. Sagittal section through left 

 side of embryo, showing exterior 

 opening of pore canal. Z 1 , lumen of 

 lobe 1 of the hydroccele; p, pore 

 canal; sp, spine; t 1 , t z , tentacles 1, 2. 

 X 233. 



Toward the posterior end of the embryo, and on each side of the 

 fifth primary tentacle, lies a spherical vesicle with a thin wall resemb- 

 ling that of the anterior enteroccele. These two vesicles probably 

 represent the left posterior enterocoele. Only in one instance could I 

 find any connection between them a very narrow canal which circles 

 around on the dorsal side of the tentacle. In all the other instances the 

 two vesicles are entirely distinct. In many specimens one of the vesi- 

 cles has divided, so that a smaller one lies just anterior to the first. 

 Sometimes this division has occurred on the right side, at other times 

 on the left, and in a number of cases the process of constriction seems 

 to be just taking place. In one specimen 2 vesicles are present on the 

 left side and 3 on the right. 



