326 THE DEEP SEA 



stones" of iron -manganese concretions other tlian a chemical flask 

 in which crystaUization takes place artificially? 



Of special interest is the problem as to when the abyssal fauna 

 originated and the old and primitive characteristics of its repre- 

 sentatives. Recently, a lively discussion has arisen about this 

 (Bruun, 1956; 1957; Zenkevitch, 1958; Menzies and Imbrie, 1958; 

 Birstein, 1959; Zenkevitch and Birstein, 1960). In this discussion 

 doubt has been cast upon the widely accepted view that the 

 intrinsic characteristics indicating that old and primitive forms 

 belong for the most part to the abyssal fauna rather than to 

 that in shallow water and that in the former there is a greater 



Fig. 2. Iron-manganese concretions at the bottom of the east Pacific, depth 

 4545 m. (Photograph after N. Zenkevitch.) 



number of "living fossils." Bruun, on the contrary, believes that 

 the present abyssal fauna is correlated with a geologically 

 young formation. Menzies and Imbrie (1958) state that the 

 "shallow water marine, the fresh water and the terrestrial en- 

 vironments have more archaic kinds of life than the abyssal 

 marine environment." This question is of great significance and 

 requires further discussion. We are inclined to believe that the 

 first viewpoint is the more probable. As for Bruun's reasoning, I 

 must refer the reader to the detailed analysis of the problem made 



