142 THE NEOG^IC REALM. [CHAP. 



accident, that a land-tortoise was carried over. Alone it could 

 not propagate. This was only possible after a similar accident 

 imported another specimen of the same species, of the other sex, 

 to the same island. Or we could imagine that at the same time 

 animals of both sexes were thus accidentally introduced. By this 

 we could at least explain the population of a single island. But 

 how did all the other islands become populated? To explain 

 this we should have to invoke a thousand accidents. The most 

 simple explanation is given by the theory of subsidence. All the 

 islands were formerly connected with one another, forming a 

 single large island ; subsidence kept on, and the single island was 

 divided up into several islands. Every island developed, in the 

 course of long ages, its peculiar races, because the conditions on 

 these different islands were not absolutely identical." 



Further evidence in favour of the same view is adduced by 

 Mr W. B. Hemsley 1 , who draws attention to the marked simi- 

 larity of the flora of the Galapagos Islands to that of the South 

 American mainland. 



The difficulty of accounting for the transport of reptiles like 

 land-tortoises across five hundred miles of sea is undoubtedly very 

 great ; yet, in the face of their volcanic nature and the depth of 

 the surrounding ocean, it is somewhat difficult to accept the view 

 that the Galapagos Islands were connected with South America. 

 In the paragraph quoted Dr Baur appears to forget that the first 

 tortoise carried to these islands may have been a gravid female ; 

 and also that if an ancestral species were established on one of 

 the islands, there would be nothing very wonderful in individuals 

 being carried to some of the others, where they might eventually 

 differentiate into distinct specific types. Moreover, it seems quite 

 within the bounds of possibility that the original introduction may 

 have been effected by means of eggs transported on natural rafts. 

 That the Galapagos tortoises were derived originally from equally 

 gigantic continental forms, may be taken for granted ; and the 

 existence at the present day of such creatures only in these and 

 the Mascarene islands is one more instance of the survival in the 

 southern hemisphere of ancient types which were formerly abun- 



1 Nature, vol. lii. p. 623 (1895). 



