SENSE-ORGANS IN MEDUSAE 
763 
the niche and rarely I have come across one in a section of the 
rhopahal canal. 
Cyanea annaskala presents, according to von Lendenfeld, a 
precisely similar arrangement of the epithelium of the niche, 
except that in this species there is a peculiar sensory apparatus 
on the dilated proximal part of the rliopalial ridge which can be 
compared to nothing in the Pelagidae. Von Lendenfeld has also 
found in Crambessa a pair of rounded thickenings containing sub- 
epithelial ganglion cells which correspond in position with the 
areas of deep columnar epithelium that I have described as extend- 
ing outward along the sides of the niche. Von Lendenfeld homol- 
ogizes these with the cone-shaped thickenings found by Claus 
in Aurelia and Chrysaora, but they seem to be something entirely 
different, as will appear later. 
The cellular covering of the extremity of the rhopalium can 
now be clearly seen to be a simple, slightl}' flattened epithe- 
lium. It grades, more gradually on the lower than on the upper 
side, into the layer of columnar cells and nerve fibers which cov- 
ers the main part of the rhopalium, fig. 10. This is similar to the 
sensory epithelium that has been found by Eimer, Claus, Schafer, 
and Schewiakoff in Aurelia, by the Hertwigs in Pelagia, by 
Schewiakoff in Carybdea, by Hesse in Rhizostoma and by Ver- 
hoffen in several species. It is a deep ciliated epithelium of slen- 
der cells with the nuclei placed irregularly in several rows. There 
are numerous straight fibers extending from the cellular layer 
through the thick felted nerve-fiber layer to the supporting mem- 
brane. These are processes of cells described in Schewiakoff's 
paper ('89) and regarded by him as supporting cells. 
On the distal side of the base of the rhopalium its epithelium 
passes into the ordinary epithelium of the niche. On the proximal 
side it grades into a peculiar epithelium that forms a structure 
of which we found the rudiments in the Pelagia-stage, fig. 32. 
This epithelium, like that on the rhopalium, overlies a layer of 
nerve fibers. It is at this stage clearly a single layer of short 
cuboidal cells provided with very long cilia, fig. 11. The nuclei 
are of the same size and appearance as in the sensory epithelium 
of the rhopalium and nearly fill the cell. The layer is very much 
