T07 



CHAPTER V. 



CCELENTERATA. 



'" Happy is he, who, satisfied with his humble fortune, lives contentedly in the 

 obscure state where God has placed him." RACINE. 



ENTERING on the sub-class of the Ccelenterata, we leave the domain 

 of the infinitely small to enter on the examination of somewhat 

 larger beings. In comparison with the Infusoria, the Ccelenterata, 

 which are sometimes of large size, are very important beings. 

 Science lately has made great advances towards giving us an exact 

 knowledge of the history of these singular animals. Many scientific 

 prejudices have been dissipated, many errors have been corrected,. 

 The Ccelenterata, as they are defined in the actual state of Science, 

 correspond not only with the Polypes, properly so called, of Cuvier 

 and De Blainville, but also with the Acalephse of the same authors. 

 We now know that certain of the Ccelenterata give origin to Medusae ; 

 and that the great majority of the organisms described as such are 

 in reality the detached reproductive bodies of certain Ccelenterates. 



Thus regarded, the Ccelenterates comprehend a great variety of 

 animals, the bodies of which are generally of a soft or gelatinous sub- 

 stance. The alimentary canal freely communicates with the general 

 cavity of the animal's body ; there is no distinct blood system ; a 

 nervous system is absent in most ; and peculiarly-constituted urticating 

 organs are almost invariably present. They are invested with a skin 

 or integument, which sometimes secretes peculiar calcareous bodies, 

 and even a. portion of the deepest-lying tissues may be invaded by 

 a calcareous deposit, the mass of which belongs sometimes to an 

 individual ; sometimes it is common to many, constituting what Dr. 

 Johnston calls the Polypidom, of which Professor Grant says, " there is 

 but one life and one plan of development in the whole mass, and this 

 depends, not on the polyps, but on the general fleshy substance of 

 the body :"* " the ramifications of the polypidom," says Dr. Johnston, 

 "are often disposed in a variety of elegant plant-like forms. The 



* "Outlines of Comparative Anatomy." 



