50 INVERTEBRATE ANIMALS. 



SUB-KINGDOM II. CCELENTERATA. 



CHAPTER V. 



1. Characters of the Sub-Kingdom. 2. Divisions. 



3. General Characters oe the Htdrozoa. 



4. Explanation op Technical Teems. 



The second gi'eat primary division or sub-kingdom of animals is 

 that of the Ccelenterata or " hoUow-entrailed " animals (Gr. koHos, 

 hollow ; enteron., intestine). This sub-kingdom embraces the Sea- 

 anemones, Corals, Sea-jellies, Sea-firs, Sea-pens, and other allied 

 animals, all of which are characterised, amongst other things, by 

 having their bodies built up of parts which are arranged in a more 

 or less star-like or " radiate " manner. Hence these creatures were 

 long known as "Radiate Animals." So many other animals of 

 different kinds were, however, included in the old sub-kingdom 

 Radiata, that naturalists have generally abandoned this term. Most 

 of the Coelenterate animals would come under the popular term of 

 " Zoophytes " or plant-animals (Gr. zoon, animal ; phuton, plant), 

 from the external resemblance which many of them bear to plants. 



The Ccelenterata may be defined as radially symmetrical animals, 

 in, loliich the mouth operas into a simple or variously divided space, 

 which represents the alimentary cavity of the higher animals. This 

 internal space may or may not he divided into t%oo portions — one 

 specially connected with digestion, and the other corresponding with 

 the hody-cavity of the higher animals. The hody-wall is composed 

 of two fundamental layers [the ^''ectoderm" and '^ endoderm"). The 

 nervous system is represented hy diffused ganglion-eells, or sometimes 

 by a simple nerve-ring ; htit there are no circulatory organs. Distinct 

 reproductive orgcau are present at some period or another of life ; hut 

 non-sexiial reproduction is very general. 



The leading feature which distinguishes the Ccelenterata, and the 

 one from which the name of the sub-kingdom is derived, is the 

 peculiar arrangement of the digestive system. In the Protozoa, as 



