CAUSES INFLUENCING THE GROWTH OF CORAL ZOOPHYTES. 65 



coral, except the depth of water ; for corals and coral reefs abound 

 on most other parts of Upolu. Below Falelatai, of the same 

 island, an equal depth was found, with no coral. Off the east 

 cape of Falifa harbor, on the north side of Upolu, Lieutenant 

 Emmons found no coral, although the depth was but eighteen 

 fathoms. About the outer capes of Fungasar harbor, Tutuila, 

 there was no coral, with a depth of fifteen to twenty fathoms ; 

 and a line of soundings across from cape to cape, afforded a bot- 

 tom of sand and shells, in fifteen to twenty-one and a half fath- 

 oms. About the capes of Oafonu harbor, on the same island, 

 there was no coral, with a depth of fifteen fathoms. 



Similar results were obtained about all the islands surveyed, as 

 the charts satisfactorily show. There is hence little room to 

 doubt tnat twenty fathoms may be received as near the range in 

 depth for reef corals; and probably the limit lies between fifteen 

 and twenty fathoms, or not far from one hundred feet. 



It may be here remarked, that soundings with reference to this 

 subject are liable to be incorrectly reported, by persons who have 

 not particularly studied living zoophytes. It is of the utmost 

 importance, in order that an observation supposed to prove the 

 occurrence of living coral should be of any value, that it be une- 

 quivocally determined whether the fragments which a lead may 

 bring up are alive or not when broken off; for a dead fragment 

 proves nothing. Even a strong impression upon the lead, show- 

 ing the form and character of the surface-cells of a coral, is not 

 wholly satisfactory, as it may have been given by a mass not liv- 

 ing. A living fragment, placed in water, will be seen to have a 

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

 servations with reference to this subject would be made with a 

 diving bell. 



Much yet remains for farther investigation. Prof. Edward 

 Forbes, in his Zoological Explorations of the iEgean, distinguish- 

 ed three separate regions of invertebrate species within twenty 

 fathoms of the surface : the first, or littoral, extending to two 

 fathoms in depth ; the second from two to ten fathoms ; the third 

 from ten to twenty fathoms.* Similar subdivisions, or others on 

 the same general principle, may yet be detected in the Pacific, in- 

 dicated perhaps by zoophytes as well as molluscs. There is no 

 evidence, however, that there are successive 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 form- 

 ation ; on the contrary, they show that the process is continuous 

 and uniform in character through the reef-growing depths. The 

 species in the lower part of the sixteen fathoms are probably differ- 

 ent from many of those above ; but they pertain to the same gen- 



* On the iEgean Invertebrata, E. Forbes, Rep. Brit. Assoc, for 1843, p. 154. 



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