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 may 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 
hydroceele near the first lobe is represented. 
Fic. 22.—Sagittal section through left 
side of embryo, showing exterior 
opening of pore canal. [/, lumen of 
lobe 1 of the hydroccele; p, pore 
canal; sp, spine; t, @, tentacles 1, 2. 
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 enteroccele. 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. 
