6 Pratt, Bipolar Theory. 



support of the theory, for it shews that a species which is 

 absent or modified beyond recognition in the tro[Hcs has 

 remained ahnost true in extra-tropical waters. 



In an account of the Holothurians of the Straits of 

 Magellan, Ludwig ('98) says " there are no bipolar species 

 in the group." He calls attention to a certain general 

 likeness of the faunas expressed by the mutual prevalence 

 of certain genera and the mutual lack of others as com- 

 pared with the tropical faunas. Ortmann does not regard 

 this as being of any consequence, and states that it has no 

 connection with the question under discussion. 



The similarity in character between the Arctic and 

 Antarctic plankton, noted by Sir John Murray, is also 

 commented upon by I. C. Thompson ('98) who records 

 the following northern species of Copepoda from Antarctic 

 waters: (i) Metridia lo)iga ; (2) OitJiona spifiifrons ; 3.ud 

 (3) Ectmosovia atlanticuvi. 



In the same paper he says : — 



" The well-known Calanus finuiarcliiais so commonly 

 "distributed through our northern latitudes, appears to be 

 "equally common about the Antarctic, and occurred in 16 

 " of the gatherings." 



Prof D'Arcy W. Thompson states that Calanus liyper- 

 " boreus \s closely allied to, if not merely a large variety 

 "of, C. finuiarchicus, which is known to occur off the 

 " Canaries in 30° N. lat., as well as off Australia in 37° S. 

 " lat., and which, according to I. C. Thompson, is also 

 " present in the Antarctic together with the species 

 " hyperborcus ; it is therefore not ' bipolar ' but ' cosmo- 

 " politan.'" 



Of this I. C. Thompson says: — "Associated with 

 " C.jimnarchicus, and fairly plentiful in some of the bottles, 

 " was the large red Arctic species C. hyperboreus, formerly 

 "passed over as a mere Arctic variety of C. finniarchicus^ 



