Growth, and Habits of Coral Zoophytes, 59 



broken off; for a dead fragment proves nothing. Even a 

 strong impression upon the lead, shewing the form and cha- 

 racter of the surface cells of a coral is not wholly satisfactory, 

 as it may have been given by a mass not living. A living 

 fragment, placed in water, will be seen to have a fleshy 

 surface, even if the polyps do not expand. The best obser- 

 vations, with reference to this subject, would be made with 

 a diving bell. 



Much yet remains for further investigation. Mr Edward 

 Forbes, in his Zoological Explorations of the ^gean, dis- 

 tinguished three separate regions of invertebrate species 

 within 20 fathoms of the surface: the yir^/, or littoral, extend- 

 ing to 2 fathoms in depth ; the second from 2 to 10 fathoms ; 

 the third from 10 to 20 fathoms.* Similar subdivisions, or 

 others on the same general principle, may yet be detected in 

 the Pacific, indicated perhaps by zoophytes as well as mol- 

 luscs. There is no evidence, however, that there are succes- 

 sive beds, composed of a distinct set of species, as has been 

 sometimes suggested. The upraised reefs of Metia afford 

 no proofs of such a mode of formation ; on the contrary, they 

 shew that the process is continuous and uniform in character 

 through the reef-growing depths. The species in the lower 

 part of the 16 fathoms are probably different from many of 

 those above ; but they pertain to the same genera in most 

 instances, and moreover there are no abrupt transitions, 

 consequently the resulting reefs should have a nearly uniform 

 character, as here stated. This fact may be better appre- 

 ciated after perusing the following chapter. 



The Nullipore zone along the reef-line, between low and 

 high tide, is clearly made out by Mr Darwin, and is one of 

 the interesting results of his investigations. It performs a 

 very important part, by the protection it gives the reef from 

 abrasion. The exposed reef is thus gathering lime from the 

 waters, and extending itself; when, if devoid of this protec- 

 tion, it would be constantly yielding to the sea. On the inner 

 reefs, where the protection is not needed, it is not given. 



* On the iEgean Invertebrata. E. Forbes, Rep. Brit. Assoc, for 1843, 

 p. 164. 



