ASIATIC INVADERS IN AMERICA 83 



basis for discussion of some of the problems referred to. 

 Other attractive inquiries, such as the influence of the Glacial 

 Epoch on animal migrations, might be elucidated. With the 

 climatic problem alone are connected so many important geo- 

 logical speculations that the subject is well worthy of a most 

 careful scrutiny. 



At a meeting of the Biological Society of Washington about 

 ten years ago the theme chosen for discussion was the sup- 

 posed former land bridge between Asia and North America. 

 Dr. F. A. Lucas spoke in favour of a geologically recent brief 

 land connection, and supported his theory by the geographical 

 distribution of the wild sheep and the brown bears of North 

 America, both of which have their near relations in Asia. 

 He also pointed to the remains of mammoth and bison in 

 Alaska as evidence of the same view. An older land connec- 

 tion, he thought, was indicated by the occurrence of a fossil 

 Nemorrhaedus in Colorado and of Elephas columbi. Dr. 

 Theodore Gill concurred with the last speaker, and suggested 

 that the presence in America of such species of fishes as the 

 pike and Scaphirhynchus tended in favour of the older land 

 connection. Mr. F. V. Coville dwelt upon the importance of 

 plants in sustaining the view of a transient and geologically 

 recent land bridge. Additional testimony in favour of an 

 old land connection of long duration was brought forward by 

 Dr. Stejneger. He particularly emphasised the occurrence 

 in Asia and America of the alligator and the salamander 

 Cryptobranchus. Dr. W. H. Dall alone dissented from the 

 opinions expressed, urging that such mammals as the 

 mammoth might have crossed over Bering Strait by an ice- 

 bridge which he thought might have joined North America 

 and Asia during the Glacial Epoch.* 



Dr. Dall f gave no reasons for his aversion to the belief 

 in a geologically recent land connection between North 

 America and Asia ; although, in acknowledging that north- 

 eastern Asia and Alaska have certain species of land and 

 fresh -water mollusks in common, he recognised the intimate 

 relationship existing between the two areas. 



* Lucas, F. A., Th. Gill, and others, "Former Land Connections." 

 t Dall, W. H., "Mollusk Fauna of Alaska and Eastern Siberia," 

 pp. 365366, 



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