MancJiester Memoirs, Vol. xlv. (1901), No. 14. 



XIV. Some Notes on the Bipolar Theory of the Distri- 

 bution of Marine Organisms, 



By Edith M. Pratt, M.Sc. (Vict), 



Honorary Research Fellotu, Owens College, Manchester. 



( Comuiunicated by Professor S.J. Hickson, M.A., F.R.S.) 



Received and read April 2^rd, igoi. 



Theel is supposed by many to be the first zoologist to 

 notice the resemblance between the north and south polar 

 faunas, but as early as 1847 Sir James Ross noted that 

 several species which inhabit the Arctic occur also in 

 Antarctic waters. Many years later Selenka ('83) and 

 De Guerne ('88) observed that certain Gephyrea inhabiting 

 the north polar seas are very nearly related to those in 

 the south polar seas. In 1886 Theel compared actual 

 specimens of Holothurids from Arctic and Antarctic 

 waters, and of them he says (p. 260) " It is a fact that, 

 " with regard to Holothurids, several forms occur in the 

 " Arctic sea which are most closely allied to those of the 

 " Antarctic." 



In explanation of the curious similarity between the 

 north and south polar faunas Pfeffer ('91) proposed the 

 " Bipolar Theory," which maintains that the many points 

 of resemblance existing between Arctic and Antarctic 

 faunas are sufficient to indicate a nearer relationship of 

 these faunas to one another than to the intervening 

 tropical fauna. He also states that the littoral marine 

 fauna is the primitive one, and from it the deep sea, 

 brackish and fresh-water faunas are derived. 



In 1896 Sir J. Murray* investigated the distribution 



• A short abstract of Murray's paper is contained in my previous paper on 

 the marine fauna of the Falkland Islands (Pratt, '98). 



September zofh, igor. 



