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 

 Coelenterates. 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. 





Rhizostotna. 



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 



