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, which 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 
