CCELENTERATA ACTINOZOA. 



131 



coral is branched like a tree, and was formerly believed 

 to belong to the vegetable kingdom. There is a rind of 

 fleshy matter which surrounds a central stony stem, just 

 as a tree is invested by its bark. This fleshy matter is 

 the crenosarc, and in it the polypes are embedded. The 

 polypes are each furnished with eight leaf-like tentacles, 

 which are fringed at the edges. The living rind secretes 

 the internal skeleton, which is composed mainly of car- 

 bonate and phosphate of lime. This skeleton, although 

 it is within the ccenosarc, taken as a whole, is really out- 

 side the polypes that is, it is not secreted within their 

 tissues, as in the sclerodermic corals. If a number of 

 sea-anemones were united together into a colony, and 

 placed round a central stem, having their bases in contact 

 with it, and -their discs outside; it is evident that, al- 

 though this stem would be within the 

 combined substance of the community 

 as a whole, it would be outside, or at 

 the base of each individual polype. In 

 some of the sclerobasic corals the 

 skeleton is horny, in others it consists 

 of alternate joints of calcareous and 

 horny matter. 



The tentacles are fringed, and these, 

 as well as the mesenteries, are always 

 some multiple of four. 



Closely allied to the red coral are 

 the dead men's fingers, and virgularia 

 or sea-rods, both of which are met 

 with in British seas. 



187. The Ctenophora (Gr. kteis, a 

 comb ; phero, I carry) are a free-swim- 

 ming, gelatinous group of actinozoons, 

 which are popularly placed among the 

 jelly-fishes. They are usually found on the surface of 

 the ocean, far from land, swimming rapidly Jby the action 

 of the cilia with which they are provided. They are very 

 abundant in the northern seas, and form the food of several 



Fia.55. BEROE, ONE OF 

 TIJE CTENOPHORA. 



