4 Pratt, Bipolar Theory. 



the warm waters of the Panama region and in the Gulf of 

 Guinea, where the Httoral fauna is of a distinctly tropical 

 character. 



In a second paper ('99) in opposition to the theory, 

 Ortmann gives a short extract from Buerger's paper on 

 the Nemertines on the subject of bipolarity, with the 

 following comments : — 



" As regards the genera, all Antarctic genera are also 

 " found in the Arctic ; Buerger says that ' a general 

 ''similarity of both Polar faunas is thus indicated'^ but the 

 "lack of 12 Arctic genera in the Antarctic does not 

 " support this view, and since he says further that neither 

 " of the faunas seems to possess very characteristic types, 

 " as do {sic) the tropics, it is evident that these 9 genera, 

 "common to both polar faunas, are also represented in the 

 "tropics. There is one genus that seems to be bipolar: 

 " Cari?tovia, which has been found on the west coast of 

 "England {C. armandi), and in the Straits of Magellan 

 " (C. patagonicay 



We have no evidence in support of Ortmann's state- 

 ment that " it is evident that these 9 genera, common to 

 both polar faunas, are also represented in the tropics." 

 When we consider how little is known of the Antarctic 

 fauna, the fact that 12 Arctic genera have not )'ct been 

 taken in Antarctic waters must not be regarded as an 

 important piece of evidence against the bipolar theory. 



If there were once a universal fauna, modification and 

 specialization, after the lapse of ages, would lead to the 

 formation of species which would be more or less limited 

 in their range of distribution ; some forms would survive 

 and be prolific in species in the north, which in the south 

 would become extinct or form only {q\^ species, or vice 

 versa ; and, as a fact, at the present time, we have many 

 species which are peculiar to the northern or to the 



