CCELENTERATA. 



CHAPTER VII. 



THE SUB-KINGDOM CCELENTERATA. 



i. CHARACTERS OF THE SUB -KINGDOM. 2. DIVISIONS. 

 3. GENERAL CHARACTERS OF THE HYDROZOA. 4, EX- 

 PLANATION OF TECHNICAL TERMS. 



THE Sub-kingdom Cceknterata (Frey and Leuckhart) may be 

 considered as a modern representative of the Radiata of 

 Cuvier. From the Radiata, however, the Echinodermata and 

 Rotifera have been removed, the entire sub-kingdom of the 

 Protozoa has been taken away, and \)i\Q Polyzoa have been rele- 

 gated to their proper place amongst the Mollusca. Deducting 

 these groups from the old Radiata, the residue, comprising 

 most of the animals commonly known as Polypes or Zoophytes, 

 remains to constitute the modern Ccelenterata. 



The Ccelenterata may be defined as animals whose alimentary 

 canal communicates freely with the general cavity of the body 

 ^somatic cavity"}. The substance of the body is made up of 

 two fundamental membranes an oiiter layer, calltd the " ecto- 

 derm" and an inner layer, or " endoderm." There are no 

 distinct neural and hcemal regions, and in the great majority of 

 the members of the sub-kingdom there are no traces of a nervous 

 system. Peculiar urticating organs, or " thread-cells" are usually 

 present ; and, generally speaking, a radiate condition of the organs 

 is perceptible, especially in the tentacles with which most are 

 provided. In all the Ccelenterata distinct reproductive organs have 

 been shown to exist. 



The leading feature which distinguishes the Ccelenterata, and 

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

 the peculiar structure of the digestive system. In the Protozoa, 

 as we have seen, a mouth is only present in the higher forms, 



