JELLY-FISH , ETC 
493 
medusae—which are well known to all who dwell on the coast, and range from one 
to seven inches in diameter—we have the most highly-developed of the simple 
Ccelenterates. Their body consists for the greater part of the circular umbrella, 
the margin of which is notched all round so as to hang down in large or small 
lobes. There are also, along the margin, from four to eight or more eye-like 
spots, and extensible filaments. At the centre of the lower side of the disc is the 
mouth, which in some forms lies at the end of a projecting stalk, and is almost 
always surrounded by several thicker folded processes for the capture of prey. 
Rhizostoma. 
In some cases the folded edges of these ribbon-like arms fuse together, leaving 
only small sucker-like apertures. Canals run from the sac-like cavity representing 
the stomach to the edge of the disc, where they enter a circular canal, often 
provided with apertures. The similarity between this apparatus of digestive 
canals, and the arrangement obtaining in the Ctenophora is then evident. The 
reproductive organs lie either in special sacs round the stomach, or merely in 
widenings of the canals. The surface of the skin is provided with innumerable 
microscopically small stinging - capsules, and, thus armed, these so-called Disco- 
medusae float about in the water, their bodies being but little heavier than the 
