386 



ZOOLOGY. 



14. The Coelenterata. Animals which, like Hydra, 

 never advance beyond the gastrula stage in the direction of 

 the development of mcsoblastic tissues constitute the great 

 phylum of the animal kingdom called 

 Ccdenterata. All animals that do ad- 

 vance beyond this stage are grouped as 

 Oedemata. 



If we regard the mode of origin of 

 the coBlom in Amphioxus (by outgrowths 

 from the archenteron) as the primitive 

 method, then we may say that the 

 primitive enleron (or archenteron) of 

 Coelenterata has been differentiated in 

 at least some of the Coelomata into two 

 cavities mesenteron and ccelom. 



The Coelenterata include a great 

 variety of organisms, almost all marine, 

 such as sea- anemones, coral-polyps, jelly- 

 fish, and forms like Hydra, but more 

 permanently fixed and branched. Such forms, in which 

 buds, formed as in Hydra, remain permanently attached to 

 the original individual, themselves budding in turn, are 

 spoken of as colonial animals (fig. 196). 



Fig. 196. A COMPOUND 

 HYDROZOON. 



(Coi-yne.) 



