228 Notices of Memoirs — Dr. J. Murray — Marine Organisms. 



abundant in the warm tropical waters, decreasing in numbers 

 towards the polar regions, and it has been shown that the pre- 

 cipitation of carbonate of lime fi'om solution in sea-water takes 

 place much more rapidly at a high temperature. The pelagic 

 larv£e of bottom-living species are always present in the warm 

 surface waters of the tropics, sometimes gi'owing to an enormous 

 size ; but they are absent from the cold polar waters and in the 

 deep sea, where the majority of the bottom-living species have 

 a direct development. 



The Arctic fauna and flora, both at the surface and at the 

 bottom, resemble the Antarctic fauna and flora, and a large number 

 of identical and closely related species are recorded from the two 

 polar areas, though quite unknown in the intervening tropical zone. 



The boundary-line between the deep-sea region and the neritic 

 province is marked out by what has been called the " mud-line," 

 where the minute organic and inorganic particles derived from the 

 land and surface waters find a resting-place upon the bottom, or 

 serve as food for enormous numbers of Crustacea, which in their 

 turn ai'e the prey of fishes and the higher animals ; this mud-line, 

 in fact, appears to be the great feeding-ground in the ocean, and its 

 average depth is about 100 fathoms along the borders of the great 

 ocean basins. 



The majority of deep-sea species are mud-eaters ; some are of 

 gigantic size ; some are armed with peculiar tactile, prehensile, and 

 alluring organs ; some are totally blind, whilst others have large 

 eyes and are provided with a kind of dark lantern for the emission 

 of phosphorescent light. The deep-sea fauna does not represent 

 the remnants of very ancient faunas, but has rather been the result 

 of migrations from the region of the mud-line in relatively recent 

 geological times. 



The " Challenger " investigations show that species are most 

 abundant in the shallow waters near land, decreasing in numbers 

 with increasing depth, and especially with increasing distance from 

 continental land.^ This is true as a general rule, especially of 

 tropical waters, but in polar regions there are indications of a moi'e 

 abundant fauna in depths of 50 to 150 fathoms than in shallower 

 water under 50 fathoms.- 



The various points touched upon regarding the distribution of 

 marine organisms, might be explained on the hypothesis that in 

 early geological times there was a nearly uniform high temperature 

 over the whole surface of the globe, and a nearly uniformly dis- 

 tributed fauna and flora ; and that with the gradual cooling at the 

 poles, species with pelagic larvee were exterminated or forced to 

 migrate towards the troj)ics, while the great majority of the species 

 which were able to survive in the polar areas were .those inhabiting 



^ See 'Challenger' Eeports, " A Summary of the Scientific Results," by John 

 Murray, pp. 1430-6, 1895. 



^ See Murray, " On the Deep and Shallow-water Marine Fauna of the Kerguelen 

 Eegion of the Great Southern Ocean": Trans. Eoy. Soc. Ediu., vol. xxxviii, 

 p. 343, 1896. 



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