CHAPTER IX 



PHYLUM CCELENTERA 



Class i. HYDROZOA. 



Hydroids and 

 Medusoids. 



Class 2. SCYPHOMEDUS^ OF 

 ACRASPEDA. 



Jelly-fishes. 



Class 3. ANTHOZOA or 

 ACTINOZOA. 

 Sea-anemones, 

 Madrepore-corals, 

 Alcyonarians, etc. 



Class 4. CTENOPHORA. 



THE Ccelentera including zoophytes, swimming-bells, jelly- 

 fish, sea-anemones, Alcyonarians, corals, and the like form 

 a very large series of Accelomate Metazoa, i.e. multicellular 

 animals without a body cavity. Their simplest forms are 

 not much above the level of the simplest sponges, but the 

 series has been more progressive. Thus many illustrate 

 the beginnings of definite organs. In their variety they 

 seem almost to exhaust the possibilities of radial symmetry, 

 and some types (e.g. Ctenophora) may be regarded as 

 pioneers of the yet more progressive bilateral "worms." 

 Many are very vegetative, deserving the old name of 

 zoophytes (which should rather be read backwards 

 Phytozoa), and in their budded colonies afford interesting 

 illustrations of co-operation and division of labour. With 

 the exception of three or four fresh-water forms like Hydra, 

 all are marine. 



GENERAL CHARACTERS 



The Ccelentera are almost always radially symmetrical 

 animals in which the primary long axis of the gastrula 

 becomes the long axis of the adult. There is no body cavity, 

 or ccelom, distinct from the digestive cavity (enteron) and its 

 outgrowths. In the lower members of the. phylum, the 



