736 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



of the same genera. Of course there are many examples among deep-water 

 fauna of a wide vertical and horizontal distribution of individual species, but 

 a relatively restricted area of habitat is characteristic of all the deep-water 

 fauna. 



This is most evident from N. Vinogradova's examination of the distribution 

 of many forms of deep-water benthos (1955-58). The invariable increase of 

 endemic forms with depth is shown by this comparison both of the three 



i.2000 





>zooo 



>3D00 



>WD 



Fig. 360. Extent of taxonomic 

 isolation of deep-water bottom- 

 living fauna of western and 

 eastern parts of the Pacific 

 Ocean at different depths (Vino- 

 gradova, 1955). 



Oceans and of some individual parts of them. This is well illustrated by the 

 Figs. 360 and 361. 



The deep-water fauna of the eastern and western parts of the Pacific Ocean 

 has in the surface zone (<2,000 m) about half of the total number of forms, 

 but at great depths (>4,000 m) less than 10 per cent of them. The same 

 phenomenon was observed from comparison between the northern and 

 southern parts of the oceans and between the oceans themselves. Further 

 research on the deep-water fauna will no doubt weaken the conception of its 

 endemic nature, but will hardly destroy it. The idea of the uniformity and 

 geographical homogeneity of the deep-water fauna was based on the con- 

 ception of the uniformity, constancy and slight changeability of the conditions 

 of its existence (t°, S% , oxygen), and on the absence of any restriction on its 



