446 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



southern forms in question became more alike and more numerous 

 proceeding south. Thus radiation rather than convergence is indicated. 



11. 



That birds, winds, or circumpolar currents, by a process of picking 

 up and setting down passengers from the continents or islands by the 

 way, established a uniformity of fauna and flora. Thus, Dr. Michael- 

 son writes (Journ. West. Aust. Nat. Hist. Soc, vol. 5, July, 1908, p. 

 13): "There is no need for the supposition of an ancient great Ant- 

 arctic continent which connected Australia and South America, as 

 some scientific men still suppose. Certain littoral Oligochseta, con- 

 sisting of euryhaline forms, for wliich the salt sea is no barrier, can be 

 transported by the west wind drift over the stations on the different 

 islands lying between one continent and another." 



The flora of the circumantarctic islands, as instanced by Kerguelen, 

 was thought by W. Schimper to have been conveyed by sea birds and 

 ocean drift (Schimper, Wissenschaft. Ergebn. Valdivia, vol. 2, 1905, 

 p. 75). Although this might apply to species which recur tlirough 

 several archipelagoes, such would not explain the presence of endemic 

 plants and on Kerguelen the occurrence of an endemic snail, AmpTii- 

 doxa hooJceri. 



Such transport accounts only for a wide range of individual species 

 capable of air or water carriage. It has doubtless been a small but 

 real factor in distribution. But it does not account for the existence 

 of related and representative species, for the subtropical element, or 

 for the species incapable of such conveyance. Prof. W. B. Benham 

 raises the objection that a species might drift yet never land: "When 

 I stood at the top of the sheer cliffs, some 500 feet to 1,000 feet in 

 height, which form the whole of the west coast of Auckland Island 

 and saw the tremendous breakers which even in moderately calm 

 weather dash with incredible force against the rocks, I was more than 

 ever convinced that the west-wind drift can not account for the 

 transference of Oligochaeta from the various land surfaces of this 

 subantarctic region." (Benham, " Subantarctic Islands of New Zea- 

 land," vol. 1, 1909, p. 254.) 



III. 



That a trans-Pacific continent conveyed to New Zealand, Australia, 

 and South America a common stock otherwise recognized as the Ant- 

 arctic element. (Hutton, Proc. Linn. Soc. N. S. Wales, vol. 21, 1896, 

 p. 36; Baur, "American Naturalist," vol. 31, 1897, p. 661.) 



This alternative seems the weakest. Had a trans-Paciiic bridge 

 really disseminated the species under discussion then they should be 

 best developed in the central remaining portion (for instance, in 

 Tahiti or Samoa) and least at the extremity (as in Chile or Tasmania). 



