THE SUB-EIINGDOM CCELENTERATA. 13 



the ocean. Like these, the cells mark only where 

 the vital tides have been, and how they have 

 acted." 



A general survey of the development of Ccelen- 

 terate animals is best deferred till definition has 

 first been given of their classes. Here, as in other 

 sub-kingdoms, too little attention has been paid 

 to vital changes succeeding what is called the 

 ** adult " condition, more especially to those w^hich 

 immediately precede the death of the organism. 

 Such phenomena, in the present instance, would 

 possess a peculiar interest ; for individuality, the 

 distinguishing characteristic of living beings, is 

 displayed by many Coelenterata in so remarkable 

 a manner, that the phraseology by which, in the 

 case of the higher animals, we are wont to de- 

 signate its manifestations, cannot to the former be 

 applied without considerable qualification. 



Excepting two fresh-water genera, all Coelen- 

 terata are marine. Few, if any, seas appear to 

 want these animals, the several forms of which, 

 both fixed and oceanic, enjoy also a varied bathy- 

 metrical range. The coral-reefs, so widely spread 

 throughout the tropics, and the floating banks of 

 jelly-fishes, amid which ships have been known to 

 sail for days, testify, in like manner, to the abund- 

 ance of a group of beings, whose place in th^ 

 general economy of nature is not less extensive 

 than significant. 



Equally numerous were the Coelenterata at 

 former periods of the earth's history, nor does 

 their wide distribution in space fail to find its 

 parallel in a long-enduring existence through 

 time. In the lower Silurian rocks Coelenterate 



