320 ORIGIN OF LIFE IN AMERICA 



dridae) are confined ;to America and New Guinea, the Aglypha, 

 a division of the Colubrine snakes, inhabit south-eastern Asia 

 and Papuasia, except one genus which is restricted to Central 

 America. The pythons are mainly Australian and southern 

 Asiatic, but a single species (Loxocemus bicolor) lives in 

 southern Mexico. The American land-snail Bulimulus, as 

 we have seen, has its nearest relation (Placostylus) in 

 Australia and the islands of the western Pacific. The geogra- 

 phical distribution of the land isopods belonging to the group 

 of Spherilloninae, from New Zealand, Australia, Polynesia, 

 south-eastern Asia and Japan to south-western North 

 America, seemed to Mr. Budde-Lund * so very peculiar that 

 he invoked a Pacific continent to explain it. As a matter ot fact 

 we have very numerous similar instances indicating a striking 

 faunistic affinity between North America and eastern Asia. 

 But these examples belong to an entirely different category 

 from the animals and plants referred to as forming the later 

 Asiatic immigration. Certain closely allied or even identical 

 forms such as the alligator, the blue-tailed skink and the 

 ground-lizard in America and eastern Asia apparently point 

 to a geologically recent faunistic interchange between these 

 countries. But alligators are known even from the earliest 

 Tertiary deposits, while the range of the ground-lizard 

 (Lygosoma) from New Zealand, Australia and southern Asia 

 as far north as Japan, indicates that the genus is probably of 

 Mesozoic origin, and that we have to deal with a remarkably 

 persistent ancient type. 



When we take a general survey of the range in North 

 America of these older Asiatic animals (and the plants per- 

 fectly agree with them), we find that their number decreases 

 as we go north-westward, but increases towards the south- 

 west and Central America. The whole stream of these ancient 

 Asiatic immigrants seems to have issued forth from the south- 

 west, precisely from the same part of North America that 

 also yielded the European colonists. It is in south-western 

 North America, I think, that we have to search for indications 

 of the older land connection with Asia, and not in the Bering 

 Strait. Another point that strikes us during our general 



* Budde-Lund, G,, "Revision of Crustacea Isopoda Terr.," II., p. 40 



