170 FORMATION OF CORAL REEFS. 



like kind that follow them in later periods. In 

 this sense the Millepores are in our epoch the 

 representatives of those early Corals, called by 

 naturalists Tabulata and Rugosa, distinguished 

 from the Polyp Corals by the horizontal floors, 

 waving in some, straight in others, whieh di- 

 vide the body transversely at successive heights 

 through its whole length, and also by the absence 

 of the vertical partitions, extending from top to 

 bottom of each animal, so characteristic of the 

 true Polyps. 



Notwithstanding these differences, they were 

 for a long time supposed to be Polyps, and I had 

 shared in this opinion, till, during the winter of 

 1857, while pursuing my investigations on the 

 Coral Reefs of Florida, one of these Millepores 

 revealed itself to me in its true character of Aca- 

 leph. It must be remembered that they belong 

 to the Hydroid group of Acalephs, of which our 

 common jelly-fishes do not give a correct idea, 

 it is by their soft parts alone those parts which 

 are seen only when these animals are alive and 

 fully open that their Acalephian character 

 can be perceived, and this accounts for their 

 being so long accepted as Polyps, when studied 

 in the dry Coral stock. Nothing could exceed 

 my astonishment when for the first time I saw 

 such an animal fully expanded, and found it to 

 be a true Acaleph. It is exceedingly difficult to 



