RADIATES. 



175 



FIG. 103. 



AURELIA AURITA (reduced). 



annular stomach, which sends an intestinal branch into 

 each arm. These tubes are accompanied by yellow 

 bodies that surround them, and constitute the liver. 



The acalepha include many species of medusae or jelly- 

 fish. These are beings 

 of a gelatinous con- 

 sistence, having vari- 

 ous colors, and bodies 

 formed like a flattened 

 disk or a rounded bell. 

 The central mouth is 

 often surrounded by 

 long tentacles, that 

 float in the water. The 

 digestive apparatus is 

 composed of tubes 



more or less ramified in the centre of the gelatinous 

 mass. This latter character is common to the acalepha 

 and the corals, and leads to the frequent union of the 

 two groups under the title coelentera. 



The medusa present brilliant colors while floating in 

 the sea, but soon fade when they are removed from the 

 water. When they are touched, most of them produce 

 on contact with the skin an itching like that caused by 

 the sting of a nettle. For this reason they are sometimes 

 known as sea-nettles. 



In the course of their development many of the me- 

 dusae pass through a series of intermediate states, and 

 furnish good examples of alternate generation. The 

 medusa produces a ciliated larva which fixes itself, and 

 at the same time its borders become lined with tentacles. 

 When these latter are acquired, the young creature re- 

 sembles a goblet with a fringed border. Then it under- 



