CCELENTERATA 



fTlHE animals included in the phylum Ccelenterata were once all 

 J_ called zoophytes, or animal plants, because of their resem- 

 blance to vegetable forms. The name Ccelenterata is derived 

 from two Greek words meaning " hollow " and " intestine," and 

 it describes the anatomical structure of e^ch member of the 

 group. They are commonly known as polyps. In the simplest 

 forms the parts which perform the different functions cannot be 

 distinguished one from the other, and even in higher forms there 

 is but little differentiation. Shakspere's description of old age 

 applies to them : " Sans teeth, sans eyes, sans taste, sans every- 

 thing." 



Nevertheless, this very low order of animals has, like the 

 higher orders, such a diversity of form and habit as to require 

 classification. Some of them are stationary, and of these some 

 branch like plants ; some move about by the aid of tentacles, some 

 move by means of vibrating cilia, and others move by the con- 

 traction and expansion of the soft body. 



Cuvier included them in his Radiata, a class comprising all the 

 animals whose parts diverge or radiate from a central axis. 

 Recent classification has divided the radiate animals into several 

 classes. This arrangement of parts is obviously quite different 

 from that of bilateral symmetry, or the disposal of parts on each 

 side of a longitudinal axis. The type of radiate structure is 

 shown in polyps. The body is a sac, in the center of which is 

 another sac or axis. This is the digestive cavity. Vertical 

 partitions extend from the central to the outer sac, forming dis- 

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