146 POPULAE HISTORY OF THE AQUARIUM. 



disturbed. They are constantly moving in tremulous un- 

 dulations ; but the vesicles above described appear to me 

 to be air-vessels placed along the edges of the folds ; and 

 it is some confirmation of this opinion, that the vesicles dis- 

 appeared when the animal was touched. 



" This arrangement of air-vessels would very materially 

 assist in keeping uppermost the convex disc of the Coral, 

 and be of vital importance to the young polype at the time 

 of separation, and, subsequently, in keeping it upon the 

 surface of its sandy bed; or if they were moved by a sud- 

 den roll of the sea, which would lift even the most ponder- 

 ous, and possibly convey them a considerable distance, they 

 would be again deposited in their natural position. That 

 they have no power of turning themselves, I proved during 

 a sojourn of six weeks at Tahiti, by placing a healthy spe- 

 cimen with its upper surface downwards, during which time 

 it remained in the position placed, and the vitality of the 

 points in contact with the rocks was destroyed. 



" In Fungia limacina, I have seen instances where the 

 Coral, having been accidentally placed, and permanently 

 fixed in such unusual positions, has adapted itself to its 

 new situation by increasing upon its edges and forming 

 a w^"^ convex surface. They seem, when young, to be 



