454 HOTES. 



rate of growth for the massive AstrEeidseof 18 feet in a thousand years, 

 whereas Dana allows at the utmost 5 feet. It is not, however, to be 

 supposed that either of these estimates is universally applicable, anoe 

 the diflferent species of corals, like all other animals, have diiierent rates 

 of growth, and the rapidity might also vary under different circum- 

 stances. It would, indeed, be extremely interesting if only the maximum 

 rapidity of growth in individual corals — as those pf different reefs — 

 could be -established -by observation ; but to do this would be a highly 

 complicated and diflScult task, since the vigour of growth of the animals 

 must depend on a great number of different influences which combine 

 to affect' it. 

 - - Note W5,page 229. I have been at great pains in seeking in books 

 of travels or descriptions of the different species of corals for data as to 

 the various forms which coral-blocks are capable of assuming in diffe- 

 rent situations, but the results of my search have been terribly meagre. 

 X found, in fact, only the observations made by Ehrenberg to the effect 

 that Stepluinocora, HemprieliU, Ehren., in the Red Sea, forms branched 

 or flattened stocks according to whether it lives in still or in rough 

 water (see Ehren. Corals of the Med Sea). This, in my opinion, is 

 the inevitable result of the faulty methods of investigation hitherto 

 applied to these creatures; naturalists are desirous of distinguishing 

 the species, and accordingly they have above everything paid attention 

 to the distinctive character— as with insects, shells, &;c.— and at the 

 time — ^like Dana in his magnificent work on corals, connected with 

 Wilkes's expedition — they have bestowed the utmost pains in ascertain- 

 ing the limits of variability for individual species, as he has done with 

 the ^eatest care in regard to certain madrepores. Klunzinger's new 

 work on the corals of the Ked Sea supplies an abundance of material 

 of this kind. But up to the present time no systematic observa- 

 tions have been carried out bearing on the question which we are 

 especially studying— as to how far currents in the sea, variations 

 in temperature, or tlie saline constituents and other physico-chemical 

 influences, may affect each species individually. The excuse to be 

 offered is evidently this: that the fundamental essence of Darwin's 

 theory is only now beginning to exert its influence, and that we are only . 

 now beginning to recognise the necessity for not merely putting off 

 these reacting conditions with an attempt at a hypothetical explanation, 

 but for throwing on them the light of carefully conducted research, and, 

 wherever it is possible, of actual experiment. Another and a very 

 serious hindrance lies in the difficulty of obtaining the living material 

 that is indispensable for such investigations; stationary zoologists, 

 quaUfled to conduct 1 hem, are not many in the tropics, and travellers 

 can never have time enough to make any really valuable observations 

 pf this kindi We must hope that we may ere long see a few zoological 

 stations estabjished ia-.the. tropioal seas, such- as that inaugurated with 



