406 EXISTENCE AND DISTRIBUTION OF MARINE ORGANISMS. 



An analysis of the Challenger's results seems to show that the deep- 

 sea organisms at present inhabiting the sea bed are not, as is generally 

 supposed, universally distributed in the abysmal area; indeed, they 

 do not seem to be much more widely distributed than shore forms 

 from any one given region. Of the 272 species taken in the deep-water 

 area of the Kerguelen Eegion, in depths of over 1,260 fatlioms, 60 per 

 cent are only known from these dredgings, and not more than 6 per 

 cent have been found in the dredgings within and to the north of the 

 tropics. Again, of the 523 species found in depths over 1,000 fathoms 

 south of the southern tropic, 64 per cent are known only from this 

 area, and only 8 per cent are known from dredgings within the tropics 

 and to the north of the northern tropic. 



The Challenger dredgings in the neighborhood of Marion, Kerguelen, 

 and Heard islands, down to a depth of 150 fathoms, gave 533 species ; 

 of these 61 per cent are unknown outside that region, while 3 per cent are 

 known from areas within and to the north of the tropics, and 6 per cent 

 are known from regions north of the northern tropic, but not within the 

 tropics. I have already stated that the number of genera and species 

 is largest in the shallow zone under 100 fathoms, and that the number 

 decreases down to the deepest water far removed from land. This 

 relation apparently holds good even in shallower depths less than 100 

 fathoms, and especially within the tropics, the number of genera and 

 species in depths less than 20 fathoms on the whole exceeds the num- 

 ber in deeper water. The statistics of the Challenger investigations in 

 the neighborhood of Kerguelen, however, seem to show that in depths 

 less than 50 fathoms the number of species and genera may be less 

 than in greater depths, for the total number of species recorded from 

 Kerguelen in depths less than 50 fathoms amounts to 242, less by 30 

 species than the number captured in 8 trawlings in depths greater than 

 1,260 fathoms, and in depths between 75 and 150 fathoms around these 

 Antarctic islands both species and individuals appeared always to be 

 more abundant than in shallower water. 



The general similarity between the fauna and flora of high northern 

 and high southern latitudes has been many times remarked, and in the 

 first dredgings of the Challenger in comparatively shallow water in the 

 southern hemisphere the naturalists were very much struck by the char- 

 acter of the fauna being very like what they had been accustomed to 

 procure in somewhat shallower water off the northern coasts of Europe; 

 the species in many cases seemed to be identical. This impression was 

 deepened as the Challenger dredgings still further to the south were 

 examined. The specialists who have described the various groups of 

 animals brought home by the Challenger frequently -call attention to 

 species from the Kerguelen Eegion being identical or closely allied to 

 species occurring in the far north, which at the same time are wholly 

 unknown from within the tropics. We are now acquainted with about 

 150 identical species of Metazoa, and nearly 100 closely allied species, 



