Coelenterata. 325 



top, each, except the first, forming a jellyfish. The sur- 

 face that was uppermost becomes the subumbrella. 



Other Jellyfishes. Most of the jellyfishes are essen- 

 tially similar to Aurelia, though they differ considerably in 

 their shape, some being conical instead of saucer-shaped. 

 They often are seen in great schools, swimming lazily by 

 gently opening and closing the umbrella, or floating at 

 the surface ; or they may sink out of sight at will. They 

 are mostly marine, and most are free-swimming, though a 

 few are permanently or temporarily attached by the exum- 

 brella surface. They are all carnivorous, feeding largely 

 on Crustacea. Most of them are very beautiful, being like 

 cut glass, or brightly colored, many being beautifully phos- 

 phorescent. The great blue jellyfish of the New England 

 coast sometimes is seven feet in diameter with tentacles 

 a hundred feet long. Smaller specimens of this sort, when 

 seen by transmitted light, as when in an aquarium, 

 resemble immense amethysts. 



CLASS III. ACTINOZOA. 



Sea Anemones. To this class belong the sea anemones 

 and most of the coral polyps. The common sea anemone 

 is hydralike, that is, it is cylindric, attached by the base. 

 The tentacles are numerous and are borne on a disk sur- 

 rounding the mouth at the free end. The mouth is an 

 elongated slit. The internal structure differs considerably 

 from that of the hydra. In the first place, the mouth 

 does not open directly into a simple body cavity, but is 

 continued as a tubular gullet, which extends halfway down 

 the body. A series of radiating partitions run the whole 

 length of the body, extending from the outside of the 

 gullet to the body wall. Below the lower end of the 



