6 Prof. T. Fuchs on the Deep-sea Fauna. 



isms commenced, it was so much thecustom to regard conditions 

 of temperature as the efficient factor, that, without further 

 consideration, it was employed for the explanation of the 

 bathymetric distribution of marine animals ; and as it was 

 found that in the sea the temperature diminished with in- 

 creasing depth, and as it was further observed that some 

 animals which are found only in the depths in the warmer 

 seas, occur in the littoral region in the boreal and arctic seas, 

 people became so thoroughly convinced of the truth of this 

 opinion, that even at the present day we find the temperature 

 almost universally regarded as the limiting factor, governing 

 not only the horizontal, but also the bathy metrical distribution 

 of marine organisms*. 



Now it certainly cannot be denied that every individual 

 species of animals is confined within certain limits of tempe- 

 rature, within which alone it finds the possibility of continued 

 existence ; and so far the limiting influence of the conditions of 

 temperature certainly cannot be denied. But, true as this 

 may be, it is equally certain, on the other hand, that the 

 universal contrast that w r e find over the whole globe between 

 the littoral fauna, on the one hand, and the deep-sea fauna, on 

 the other, is in no way connected with the conditions of tempe- 

 rature, and must be brought about by some quite different 

 conditions. 



Dana has already repeatedly and emphatically pointed out 

 that temperature plays only a very subordinate part in the 

 distribution in depth of sea-animalsf ; and the facts which 

 may be cited in favour of this are of so convincing a nature 



that one cannot help wondering how such an opinion as the 

 above could so long prevail. 



The reef-forming corals require in order to thrive an 

 average temperature of 23°-25° C. (73°-77° F.) j and it should 

 never fall below 20° C. (68° F.)- But, according to recent 

 investigations, throughout almost the whole of the tropical 

 part of the Pacific Ocean a temperature of 25° C. prevails at 

 a depth of 80 fathoms, and of 21° C. (70° F.) down to 100 

 fathoms; and consequently, so far as it depends upon tempe- 

 rature alone, the reef-building corals, with the whole wealth 

 of their fauna, might occur nearly to 100 fathoms. Never- 



* Thus, even quite recently, in the general introduction to the zoolo- 

 gical publications of the * Challenger ' expedition, Thomson treated tem- 

 perature as the most important factor in the distribution of marine animals 

 in depth. 



t bee, for example, Dana, " On the question whether Temperature de- 

 termines the Distribution of Marine Species of Animals in Depth n ( Amer. 

 Journ. vol. xv. 1853, p. 204). 



