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,* T 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 south¬ 
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 winters 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 Adams f and Dr. Brown ^ 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 soutli-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, C. C., “ South-Eastern States as a Centre of Distribution,” 
p. 121. 
+ Adams, C. C., “ Post-Glacial Dispersal of North American Biota.” 
\ Brown, A. E., “ Post-Glacial Nearctic Centres of Dispersal.” 
