S80 AUSTRALIA : 



to tropical latitudes is intelligible ; but why, with the excep- 

 tion of the Bermudas, there should not be a single coral isle 

 or reef in the great expanse of the Atlantic, it is hard to 

 explain. Had the Bermudas themselves been absent, a 

 certain general conjecture might have been hazarded, which 

 their actual position and coralline structure render inad- 

 missible. Volcanic action, ancient or recent, affords no ex- 

 planation of this partial distribution ; nor do any ascertained 

 differences in the depth or bottom of the sea, or in the 

 mineral contents of different seas, come in aid of the solu- 

 tion. A supposition is still open, vague perhaps in its 

 application to the present case, yet supported by many ana- 

 logies drawn from other parts of the animal world. The 

 corals, in their pulpy portion, afford food to several species 

 of fish and to the whole tribe of Holothurise ; while they 

 themselves, simple and minute though they be, must feed on 

 some other kinds of organic life. There may be in certain 

 seas a predominance of the animals destroying them, or a 

 deficiency in those affording them nutriment. In either of 

 these conceivable cases we bring the question among those 

 curious instances (now almost forming an especial branch of 

 natural history) in which the existence, range, multiplica- 

 tion, or extinction of species, are determined, not merely 

 by inanimate agents around, but by the presence or absence, 

 abundance or scarcity, of other species in the same regions 

 and at the same periods of time. We might say much as to 

 this interesting and prolific course of enquiry, did it come 

 within our present subject. 



The manner and rate of growth of corals offer other curious 

 questions to the naturalist. The evidence as to the latter 

 point is various, and on first view somewhat contradictory. 

 With some well-attested examples of rapid growth (the 

 filling up of channels and lagoons, and enlargement of 

 islands within human record) we have other instances where 



