FORMATION OF CORAL RKEFS. 171 



obtain a view of them in this state, for, at any 

 approach, they draw themselves in, and remain 

 closed to all investigation. Only once, for a 

 short hour, I had this opportunity ; during that 

 time one of these little creatures revealed to me 

 its whole structure, as if to tell me, once for all, 

 the story of its existence through all the succes- 

 sive epochs from the dawn of Creation till now, 

 and then withdrew. With my most patient 

 watching, I have never been able to see one of 

 them open again. But to establish the fact that 

 one of the Corals represented from the earliest 

 period, and indeed far more numerous in the 

 beginning than any other, was in truth no 

 Polyp, but an Acaleph, the glimpse I had was 

 all-sufficient. It came out as if to bear witness 

 of its class, — as if to say, '* We, too, were 

 among the hosts of living beings with which 

 God first peopled his earth." 



With these branching Corals the reef reaches 

 the level of high-water, beyond which, as I have 

 said, there can be no further growth, for want of 

 the action of the fresh sea-water. This depend- 

 ence upon the vivifying influence of the sea ac- 

 counts for one unfailing feature in the Coral 

 walls. They are always abrupt and steep on the 

 seaward side, but have a gentle slope towards the 

 land. This is accounted for by the circum- 

 stance that the Corals on the outer side of the 



