THE BALTIC SEA 



337 



У -Г / 





&Л 



Fig. 1 64. Distribution of Myoxocephalus quadricomis (A) in the Sea 

 and the lakes (B) of* Sweden (Ekman). 



Several such forms are found in the southeastern part of the North Sea. 

 The Baltic Sea, stretching far from south to north, and with a very severe 

 climate in the north, provides a most favourable environment for the pre- 

 servation of cold-water relicts. It is possible that low temperature, rather than 

 salinity, promotes the existence of Arctic brackish- water relicts in the northern 

 part of the Baltic. 



The same can be seen in the case of polychaetes. It follows from the zoo- 

 geographical analysis of this group given by A. Friedrich (1938) that, whereas 

 for the North Sea and the Baltic together the boreal, Lusitanean and Lusi- 

 tanean-boreal species form 53-2 per cent, and the Arctic, Arctic-boreal and 



Fig. 165. Distribution of Mysis oculata in the Sea (A) and 

 M. o. relicta in the lakes of Sweden (B) (Ekman). 



