362 POLAR PROBLEMS 



differs entirely from anything in the Arctic. For the progenitors of 

 this, he holds, we must look to the Tertiary Antarctic fauna and to 

 the pre-Tertiary Pacific. 



However, the bipolarity problem may not be allowed to rest 

 here, for as often as the theory is "discredited," it seems certain to be 

 resurrected in one phase or another. Theel,^^ in a careful review, points 

 out the indubitable bipolarity of certain priapulids, shallow-water 

 wormlike organisms quite incapable of distant transportation in either 

 the adult or larval stages and unknown, in the case of the bipolar spe- 

 cies, from regions intervening between the two polar oceans. Such 

 a phenomenon, he maintains, cannot be due to convergence and is 

 one of a number of examples of true bipolarity which fully meet the 

 requirements laid down by Thompson and which demand a specific 

 interpretation. The one which Theel offers uncompromisingly harks 

 back to the original idea that such organisms are "relicta, that their 

 progenitors had a world-wide distribution, and that they are in posses- 

 sion of a remarkable power of resistance." 



Still more recently, Benham-^ reports the discovery of another 

 Arctic species of this same vermiform group (Phascolosoma eremita) 

 at a depth of 318 fathoms in Commonwealth Bay, Adelie Land. The 

 species is widespread in Arctic seas, and Benham believes that its 

 addition to the list of bipolar species strengthens Theel's views. 



The whole subject, as Thompson has said, needs argument less 

 than investigation. The importance of a group of animals in rela- 

 tion to any problem of distribution depends, first, upon the thorough- 

 ness of the collecting throughout the entire range and, then, upon the 

 extent to which classification has been correctly worked out. Further 

 elucidation of bipolarity, which can evidently no longer be accepted 

 in its broad and naive sense, rests especially upon scrupulous sys- 

 tematic work. Murray tells us that the greatest difificulties encoun- 

 tered during the classification of the Challenger collections were due 

 to the extraordinary number of species and genera of marine inverte- 

 brates found to possess reduplicated names. Possibly he was not even 

 wrong in assuming that the northern and southern seas would now 

 show many more common or closely allied species but for the fact 

 that systematists are often prone to regard discontinuity as sufficient 

 reason for making the most of very slight differences. 



The inherent weakness in the bipolar hypothesis is touched by the 

 question "What has now become of the tropical representatives of 

 the formerly universal fauna?" The inference seems to be that, owing 

 to the higher rate of metabolism in warm water, the primordial or- 



2' Hjalmar Theel: Priapulids and Sipunculids Dredged by the Swedish Antarctic Expedition, 

 1901-1903, and the Phenomenon of Bipolarity, K. Svenska V elenskaps.-Akad. Handl., Vol. 47, 191 1, 

 No. I, pp. 1-36. 



" W. B. Benham: Gephyrea Inermia (Australasian Antarctic Expedition 1911-1914, Scientific 

 Repts., Ser. C: Zoology and Botany, Vol. 6, Part V), Sydney, 1922, pp. 1-22. 



