74 MANUAL OF ZOOLOGY. 



CCELENTERATA. 



CHAPTER VII. 

 THE SUB-KINGDOM CCELENTERATA. 



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

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

 PLANATION OF TECHNICAL TERMS. 



THE sub-kingdom Cczlenterata (Frey and Leuckhart) may be 

 considered as the modern representative of the Radiata of 

 Cuvier. From the Radiata, however, the Echinodermata and 

 Scokcida have been removed to form the Annuloida, the entire 

 sub-kingdom of the Protozoa has been taken away, and the 

 Polyzoa have been relegated 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 denned 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 outer layer, called the " ecto- 

 derm" and an inner layer, or " cndoderm? 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. By Professor Allman the Ccelenterata have 

 been defined as follows : " Animals composed of numerous 

 merosomes (body-segments), which are disposed radially round 

 a longitudinal (antero-posterior) axis ; frequently with a 

 determinable antero-posterior and dorso-ventral plane (bi- 

 lateral) ; a distinct body-cavity, which always communicates 

 with the outer world through the mouth." 



