No. 391.] BIPOLARITY OF MARINE FAUNAS. 59 1 



sea (Ortmann, von Ihering, Thompson, Chun, Ludwig) ; (2) con- 

 nection along the western shores of the continents, mostly con- 

 nected with a descending of the respective forms into deeper 

 water (Ortmann, Bouvier, Thompson, Ludwig). 



It is possible that by these ways cases of true bipolarity may 

 develop, provided these connections become discontinued. The 

 writer has explained a true case of bipolarity (Crangon) by one 

 of these ways. But, on the other hand, it is also possible that 

 bipolarity is to be explained by the Pfeffer-Murray theory in 

 some cases by former conditions of the earth's history, espe- 

 cially those existing at the beginning of the Tertiary period. 

 Yet we do not know any concrete case of this kind, and we 

 must wait for further investigation to show whether bipolarity 

 as a relic of older times is realized in the geographical distribu- 

 tion of any marine animals. 



