SUB-KINGDOM ILC(ELENTERATA. 

 CHAPTER IV. 



1. CHAEACTEES or THE SUB-KINGDOM. 2. DIVISIONS. 



3. GENEEAL CHAEACTEES OF THE HYDEOZOA. 



4. EXPLANATION OF TECHNICAL TEEMS. 



IN the sub-kingdom Ccelenterata are included the sea- 

 anemones, corals, sea-jellies, sea-firs, and other allied animals, 

 and the whole division may be looked upon as forming the 

 most typical section of the animals formerly called by Cuvier 

 Radiata. In addition, however, to the above-mentioned ani- 

 mals, Cuvier included in his Radiata all the members of the 

 modern sub-kingdom Protozoa, together with the sea-mats or 

 lowest class of the Mollusca, and the sea-urchins, star-fishes, 

 wheel-animalcules, internal parasites, and others which are 

 now placed in a separate sub-kingdom by themselves (Annu- 

 loida). The old Radiata, therefore, was an extremely hetero- 

 geneous assemblage, and there is no advantage to be derived 

 from its employment even in works such as this present. The 

 division Ccelenterata, or " hollow-entrailed " animals (Gr. 

 Jcoilos, hollow; and enter on, intestine), includes all those radi- 

 ate animals which are more or less closely allied to the sea- 

 anemones on the one hand, and to the sea-firs on the other. 

 Most of the Ccelenterata come under the conveniently loose 

 term of " zoophytes," or plant-animals, from the external re- 

 semblance which many of them show to plants. 



The Ccelenterata may be defined as animals whose aliment- 

 ary canal communicates freely with the general cavity of 

 the body ^somatic cavity"). The body is essentially com- 

 posed of two layers or membranes, an outer layer or " ecto- 

 derm," and an inner layer or " endoderm" No circulatory 

 organs exist, and in most there are no traces of a nervous 



