AURELIA. 129 
The mouth passes by a short cesophagus into a gastric 
cavity which is produced into four pockets in the inter-radii. 
Each pocket contains on its oral wall a horse- 
shoe-shaped goad, and near the middle a row 
of gastric filaments which assist in digestion. 
The gastric cavity is continued outwards towards the edge 
of the disc by numerous vascular canals. The eight primary 
branched canals are the four per-radial and the four inter- 
radial. Between these there are the eight secondary .un- 
branched canals or ad-radials. Allthe canals open into a ring- 
canal round the edge of the disc. The gastric cavity and the 
canals are ciliated. They are derived from the ccelenteron, 
as'in Odelia. In the inter-radii, immediately below the 
gonads, are four swb-genital pits, each opening on the oral 
surface by a pore. 
The mesogloea between the two layers is a thickened 
jelly which in this case contains scattered cell-elements. 
Internal 
Features. 
Fig. 61.—MEDIAN LONGITUDINAL SECTION THROUGH THE INTER- 
RADIAL PLANE OF AURELIA. (Diagrammatic. ) 
Gastric Filaments. 
Sub-genital Pit. | Stomach. 
Gonad, 
Inter-radial Canal. 
Ring-canal. 
Lappet. 
Tentaculocyst. 
Oral Tentacle. Mouth. 
There is no nerve-ring, but there is a diffuse nerve-plexus 
concentrated round the sense-organs or ‘¢entaculocysts. 
These latter are complex and appear to unite the senses of 
sight, hearing and smell in different parts. 
DEVELOPMENT. — Aurelia is dicecious and the sexual elements 
are discharged by the mouth. A free-swimming planula larva (Chapter 
V.) settles down on rocks or weeds and forms .the Aydra-tuba, a minute 
hydra-like individual. It is a two-layered sac, with a mouth at the 
M. To 
