154 PHYLUM CQ@LENTERA. 
Alimentary system.—The four corners of the mouth are 
extended as four much-frilled lips, each with a ciliated 
groove and stinging cells, and with an axis of mesoglcea. 
They exhibit considerable mobility. Their crumpled and 
mobile bases surround and almost conceal the mouth. A 
short gullet or ‘‘manubrium” connects the mouth with the 
digestive cavity in the centre of the disc. From this central 
chamber sixteen gastro-vascular canals of approximately 
equal calibre radiate to the circumference, where they open 
into a circular canal, with which the hollow tentacles are 
connected. Eight of the radial canals are straight, but the 
other eight are branched, and thus in an adult Aurelia the 
total number of canals is large. These canals are really due 
to a partial obliteration of the gastric cavity by a fusion of 
its ex-umbrellar and sub-umbrellar walls along definite lines. 
They are all lined by ciliated endoderm. 
Where the gullet passes into the central digestive cavity, 
there are four strong pillars of thickened sub-umbrellar 
material. Beside these pillars, there are four patches 
where the sub-umbrellar surface remains thin. These are 
the gastro-genital membranes, lined internally by germinal 
epithelium (Fig. 74, &.). 
To the inside of these genital organs, within the digestive 
cavity, are four groups of mobile gastric filaments (g.f,, Fig. 
74), which are very characteristic of jelly-fish. In appear- 
ance these are very similar to the small tentacles of the 
margin, and, like them, are hollow. ‘They are covered with 
endoderm—with ciliated, glandular, muscular, and stinging 
cells. 
The body is mapped out into regions by the following convention : 
The first tentacles to appear in the larva are four in number, and 
correspond to the four angles of the mouth; the radii on which they 
appear are called ‘‘perradial,” marked by the four lips. Half-way 
between these, four ‘‘interradials” are then developed, marked by the 
gonads and gastric filaments. Then eight ‘‘adradials” may follow, 
between perradii and interradii, marked by the eight unbranched 
radial canals. 
Reproductive system.—The sexes are separate. The 
reproductive organs—ovaries or testes—consist of plaited 
ridges of germinal epithelium, situated on the four patches 
already mentioned, within sacs which are derived from and 
