174 ORIGIN OF LIFE IN AMERICA 



mitted. We may as well collect the facts tending to support 

 this theory as we proceed, since a great accumulation of 

 material in one place might appear wearisome. 



The distribution in America of one of the genera of earth- 

 worms (Diplocardia), on which glass-snakes largely live, 

 somewhat resembles that of the glass-snakes in America. 

 There is a species in Florida and three in Carolina. Further 

 north the genus appears in Illinois and Nebraska and we also 

 have a couple of species in Mexico and Lower California. 



It was Professor Adams,* I think, who first directed atten- 

 tion to the presence of two very distinct and powerful centres 

 of dispersal, one in the south-east and one in the south-west. 

 Although I am by no means so impressed, as Professor 

 Adams and Dr. Brown are, by the significance of the soutih- 

 eastern centre of dispersal as compared with the south- 

 western one, which is incomparably more important, I quite 

 concur in their opinion that the former faunistic centre is 

 perfectly recognisable. These writers moreover discuss the 

 problem which I have dwelt upon so many times above, viz., 

 that of the climate during the Ice Age. 



Having adopted the current views of the existence of giant 

 glaciers in the northern United States accompanied by 

 an arctic climate Professor Adains f and Dr. Brown J were 

 obliged to search for suitable " biotic preserves'" where the 

 pre-Glacial fauna could have safely weathered the Ice Age. 

 These they discovered in the two centres of dispersal alluded 

 to, in the south-east and south-west, and from them they sup- 

 pose the waves of migrants to have streamed forth northward 

 after the Glacial Epoch was over. The presence of a few 

 stray remains of northern animals south of their present 

 habitat lent a certain amount of credence to the theory in a 

 southward extension of the arctic climate. But we must 

 remember that these northern creatures, when actually 

 pressed out of their boreal home by a restriction of 

 their habitats, found themselves in the northern United 



* Adams, 0. C, " South-Eastem States as a Centre of Distribution," 

 p. 121. 



+ Adams, 0. C, " Post-Glacial Dispersal of North American Biota." 

 X Brown, A. E., "Post-Glacial Nearctic Centres of Dispersal." 



