No. 391.] BIPOLARITY OF MARINE FAUNAS. 585 
pelagic faunas of the Arctic and Antarctic, by C. Chun.! He 
collects the records of the occurrence of the animals constituting 
the plankton of the polar regions (Protozoa, Medusze, 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. 
