252 ORIGIN OF LIFE IN AMERICA 



islands. Dr. Gadow next proceeds to argue that because one 

 of these coecilians inhabits eastern Mexico, its ancestors must 

 have travelled slowly across the whole neck of Central America 

 since the close of the Miocene Epoch, when he assumes the 

 isthmus to have been first opened up for southern immigrants. 

 This argument is in so far faulty, as the coecilians need not 

 necessarily have passed through Central America. The inti- 

 mate relationship that exists among many ancient species of 

 Central America to those of northern South America suggests 

 the existence of some far older link between these countries. 

 In very remote times species were, I believe, able to reach 

 certain areas such as Guatemala and western Mexico long 

 before the present Central America had com into existence, 

 that is to say long before Pliocene times. Dr. Gadow himself 

 urged that the Isthmus of Panama is but the last vestige of a 

 former much broader land connection between North and 

 South America (p. 243). In my opinion this should read 

 " the Isthmus of Panama contains some vestiges of a former 

 much broader land connection." 



To the uninitiated the Typhlopidae would seem nearly 

 related to the coecilians. Both are snake-like burrowing crea- 

 tures, and yet the former are true snakes and, therefore, 

 reptiles, while the others are merely limbless amphibians. On 

 close examination the true burrowing-snakes (Typhlopidae) 

 are found to be covered with minute cycloid scales, and to 

 exhibit other reptilian characters. Their distribution is ex- 

 tremely discontinuous and extensive, and they are largely 

 confined to solitary islands. That they possess no special 

 facilities for accidental dispersal across the ocean is evident, 

 and yet it is held by some zoologists that their presence on 

 islands, such as Christmas island for instance, can only be 

 due to such a cause. A't any rate, the family exhibits all the 

 signs of antiquity, and, in the absence of any positive evidence 

 of accidentally distributed species, I am firmly convinced that 

 they spread by the usual method of slow migration on land. 

 Dr. Sarasin * places the dispersal of the family into pre- 

 Cretaceous times, in spite of the fact that we possess no 

 palaeontological evidence of their antiquity. All the same he 



* Sarasin, F., "Tierwelt von Ceylon," p. 75. 



