764 
ROBERT PAYNE BIGELOW 
folded and pitted. The mesogloea, however, takes no part in 
this folding, but the nerve fibers extend outward between the 
cells which line adjacent pits. This folded epithelium covers a 
small part of the lower surface of the rhopalial ridge (fig. 10) and 
extends along the lateral grooves into the pockets that have been 
mentioned as being sunk into the mesogloea at the sides of the 
mouth of the rhopalial canal. The pits are thickly set and in the 
lateral pockets they are very deep and fill nearly the whole of the 
pocket. The lumen of each pocket opens into the fundus of the 
niche on one side of the ridge, figs. 2 and 11. The pocket is much 
wider horizontally than vertically and is deeper than the proxi- 
mal wall of the niche, so that its apex occupies a small prominence 
in the roof of the gastric pouch at the sides of the mouth of the 
rhopalial canal, figs. 8 and 9. 
This pitted ectoderm is separated from the endoderm by only 
a thin supporting membrane for the whole distance from the base 
of the rhopalium to the apex of the pocket. From this point the 
mesogloea thickens and then the endodermal lamella appears and 
continues in contact with the pocket around to its adradial ex- 
tremity, fig. 8. I cannot, however, discover any protoplasmic con- 
nection between the cells of the lamella and those of the pocket. 
The nerve-fiber layer which lines the pocket and underlies the 
whole of the pitted epithelium is of the same character as the nerve 
layer of the rhopalium, being a felted mass of extremely fine 
fibers, and is directly continuous at the base of the rhopalium 
(fig. 11) with the limbs of the U-shaped thickening which I have 
described in the previous stages. This thickening is now very 
prominent on the rhopalium and the membrane beneath it is 
thickened for its support, fig. 5. 
The pitted epithelium of the lateral grooves and pockets is, of 
course, derived from the lateral folds of ectoderm of the previous 
stage. Structures of the same kind were probably seen by Eimer 
and certainly were by Claus in Cyanea and in Aurelia, respec- 
tively. Eimer ('77) says that in Cyanea the ectoderm surround- 
ing the rhopalium forms numerous conical ingrowths. Claus 
('77) in speaking of Aurelia says that there is found at the base 
