The Pluteus of Laganum sp. 135 
encircling a region slightly anterior to the center, beneath which lies 
the ring of the hydroceele. Here, then, the adult mouth is evidently 
to form. 
The wall of the amniotic cavity is composed of 2 layers of tissue 
which are continuous with each other around the external opening. 
They consist of an inner layer of large irregular cells, and an outer 
epithelium of cylindrical cells with darkly staining nuclei, usually 
situated well back toward the base of the cell. In the inner layer the 
cytoplasm is clear, and takes the form of a loose, irregular meshwork ; 
in the outer it is opaque and is crowded with pigment granules exterior 
to the row of nuclei. Occasionally, however, large areas may be found 
in the outer layer, within which the cytoplasm contains many irregular 
vacuoles, indicating that possibly the wall of the amniotic cavity 1s 
beginning to break down. 
Fig. 17.—Tramsverse sec- 
tion through anterior part 
of body, showing two 
anterior primary tenta- 
cles. a.e., anterior en- 
teroceele; 2, 3, lumen of 
lobes 2, 3, of hydroccele; 
sp, spine; @, #, tentacles 
2,3. X 233. 
Histologically, the spines also are composed of 2 layers of tissue. 
The inner central one forms a core in which the cytoplasm possesses a 
large irregular meshwork. In the outer the cytoplasm is denser and 
crowded with pigment granules, and the nuclei stain more heavily 
with the hematoxylin. Between these two layers lie well-developed 
longitudinal bands of muscle. Within the spines were originally the 
skeletal supports described above, which have been destroyed in these 
specimens by the fixing fluid. 
THE ENTEROCELES. 
Within the embryo, transformation from larva to adult is already 
beginning to take place. The gut has lost its opening to the exterior, 
the left posterior enteroccele is definitely constricted from the anterior, 
and the hydroccele with its 5 primary tentacles is already in an ad- 
vanced stage of development. 
