124 OKIGIN OF LIFE IN AMERICA 



about this blue-tailed skink is that a species, until recently 

 considered absolutely identical with it, is found in Japan, 

 being unknown on the mainland of Asia. Some differences 

 have now been detected between these two skinks, but they 

 are no doubt very closely related to one another. We are con- 

 fronted, therefore, with the extraordinary problem how to 

 account for the occurrence of two species, so nearly akin, 

 in localities so distant from one another. It must be clear to 

 anyone who is familiar with distributional problems that acci- 

 dental dispersal within recent times either by man or by 

 any other agency is out of the question. This is a case of 

 geographical distribution which must be explained by the 

 ordinary modes of migration. If it was quite a unique 

 instance of such a remarkably discontinuous range, it might 

 be a matter of some difficulty to discover a plausible explana- 

 tion to account for it. But it is by no means the only example 

 of such a range. Quite a number of instances are known. A 

 still more striking one is that of the so-called ground lizard 

 (Lygosoma laterale).* 



The ground lizard, with its minute limbs, thick tail arid 

 sluggish movements, reminds one more of a salamander than 

 a lizard. It lives, moreover, under the bark of trees or among 

 rotten wood, and is thus altogether different in habits from 

 the ordinary lizard. Now this peculiar ground lizard occurs 

 in identically the same form in North America, in China and 

 Japan. f The most searching comparison by the best experts 

 has hitherto failed to elicit the slightest difference between 

 the Asiatic and this North American ground lizard. 



It is interesting to note that the ground lizard and 

 the blue -tailed lizard, both of which exhibit such a remark- 

 ably East Asiatic relationship, are members of the family 

 Scincidae. But, whereas we possess in America over thirty 

 species of the genus Eumeces, to which the blue-tailed 

 lizard belongs, there are only two American species of, 

 Lygosoma. We now have to ascertain whether these two 

 genera Eumeces and Lygosoma, are of American origin, or 



* Cope, E. D., " Crocodilians, lizards and snakes of North America," 

 p. 622. 

 t Stejneger, L., " Herpetology of Japan," p. 219. 



