TYPES OF C@LENTERA—AURELIA AURITA. 153 
canals, and is ciliated throughout. The mesogloea is a 
gelatinous coagulation containing wandering amoeboid cells 
from the endoderm. The whole animal is very watery ; 
indeed, the solid parts amount to not more than 10 per 
cent. of the total weight. Yet some jelly-fish (species of 
Rhopilema) are used as food in Japan! 
Nervous system.—The nervous system consists—(a) of a 
special area of nervous epithelium, associated with each of 
the eight sense organs, and (4) of numerous much-elongated 
bipolar ganglion cells lying beneath the epithelium on the 
under surface of the disc. This condition should be con- 
trasted with the double 
nerve-ring in Craspedote 
medusoids, but too much 
must not be made of the 
contrast, for a nerve-ring 
is described in Cubo- 
medusz, one of the orders 
of Acraspedote jelly-fish. 
In Aurelia the sense organs 
are less differentiated than 
in many other jelly-fish. 
Each of the eight organs, 
protected in a marginal 
niche, consists of a pig- Fy, 73.—Surface view of Aureloa,— 
mented spot, a club-shaped From Romanes. 
projection with numerous Showing four genital pockets in centre, 
6c ; m4 much branched radial canals, eight peri- 
calcareous otoliths -_ pheral niches for sense organs, and peri- 
its cells, and a couple of _ pheral tentacles. 
apparently sensitive pits or 
grooves. The sense organs arise as modifications of 
tentacles, and are often called “‘tentaculocysts” or “rho- 
palia.” Their cavities are in free communication with 
branches of the radial canals. 
Muscular system.—Between the plexus of nerve cells. 
and the sub-umbrellar mesogloea there are cross-striped 
muscle fibres, each of which has a large portion of non- 
contractile cell substance attached to it. They lie in ring- 
like bundles, and by their contractions the medusa moves. 
Unstriped muscle fibres are found about the tentacles and 
lips. 
