130 
ORIGIN OP LIFE IN AMERICA 
in North America the climate of that region must have been 
very different from what it is at present. 
I may just mention two other examples of innocuous snakes 
which frequent the north-eastern States, viz., the smooth 
green snake (Liopeltis vernalis), and the rough green snake 
(Cyclophis aestivus). The former is abundant in New York 
State and northward as far as south-eastern Canada. South¬ 
ward it ranges to the Gulf of Mexico and westward to New 
Mexico, becoming rarer as we approach the drier and warmer 
districts. The other does not extend nearly so far north. On 
the other hand, the rough green snake is found westward as 
far as northern Mexico and California. Both of them share 
the peculiarity of being the only members known in America 
of the genera to which they belong. That is not the only fea¬ 
ture of interest about their distribution. I have just urged 
that the ancestors of the American species of Tropidonotus 
must have come from Europe. We cannot claim the same 
origin for the American species of Liopeltis and Cyclophis, 
for neither of these genera inhabits Europe. Both of them are 
absent also from Africa. Their headquarters are in southern 
and eastern Asia, but they do not extend as far north as Japan. 
Formerly these snakes were classed among that insoluble 
zoogeographical enigma, namely, the group of animals and 
plants peculiar to eastern Asia and eastern America. Now 
we have advanced in so far as we have been able to trace 
some of the eastern forms to an originally western American 
range. It has been made easier, therefore, for those natura¬ 
lists who are in the habit of explaining anomalies of dis¬ 
tribution by the convenient flotsam-jetsam theory, to bring 
their views to bear upon problems such as those suggested 
by the two green snakes. That these snakes could have been 
floated across the Pacific Ocean on a raft by any possible 
chance, is to me inconceivable. That they should have utilised 
the Bering Strait land connection, and subsequently have 
become extinct all along north-eastern Asia and north-western 
North America does not appeal to me either as likely. We 
must only leave the consideration of the problem for the pre¬ 
sent, as was done in the case of the lizard genera Eumeces 
and Lygosoma, which also apparently had an east Asiatic 
origin. 
