No. 391.] BIPOLARITY OF MARINE FAUNAS. 585 



pelagic faunas of the Arctic and Antarctic, by C. Chun. 1 He 

 collects the records of the occurrence of the animals constituting: 

 the plankton of the polar regions (Protozoa, Medusae, worms, 

 crustaceans, mollusks, Tunicata, and fishes), and although he 

 complains in many cases of a general lack of information, 

 especially as to the Antarctic pelagic life, he reaches some 

 very important conclusions. He recognizes a general simi- 

 larity of both faunas, which finds its chief expression in the 

 prevalence of certain groups in both areas and the absence of 

 others ; and, further, he mentions the presence in both polar 

 seas of two identical species, one a worm (Sagitta hamata), the 

 other a Tunicata (Fritillaria borealis). The first case, that of 

 Sagitta hamata, is treated more in detail, and Chun shows (after 

 Steinhaus and Lohmann) that this species, which has been found 

 near the surface in both polar seas, crosses the Atlantic Ocean. 

 It is not, however, found there near the surface, but at consid- 

 erable depths (300-1500 m.). Thus, for this pelagic species, a 

 connection of the Arctic and Antarctic range through the trop- 

 ics, but in deeper water, is established (analogous to the con- 

 nection of littoral polar forms along the bottom of the deep sea), 

 and Chun concludes that this connection, once having been 

 proved, is sufficient to explain other cases, and that there is 

 no need to have recourse to theories which, like Pfeffer's and 

 Murray's, go back to former climatic conditions of the earth. 

 Yet in the writer's opinion this conclusion is not satisfactory. 

 We do not want to know how an individual case may be 

 explained, but we want to know how it can be explained cor- 

 rectly. Although we must appreciate the value of the case 

 represented by Sagitta hamata, still there remains the question 

 to be settled, whether other cases of bipolarity, which may 

 be discovered, are really cases of bipolarity, where there is 

 no connection of both ranges, and whether such cases are to be 

 explained by the Pfeffer-Murray theory, or by other means, as 

 indicated by the present writer. But at any rate Chun's paper 

 shows plainly that cases of bipolarity among pelagic organisms 

 seem to be very rare. 



1 Die Beziehungen zwischen dem arktischen und antarktischen Plankton. Stutt- 

 gart, 1897. 



