3i6 SCIENCE PROGRESS 



the connection between Africa and Brazil, which is indicated 

 by several independent lines of evidence, was still in exist- 

 ence. He also quotes, on page 156 of the memoir cited, 

 Messrs. Baron and Baker to the effect that botanical and 

 geological evidence indicates not only the union of Madagascar 

 with Africa during the Miocene, but likewise the inclusion of 

 the Mascarenes and Seychelles, and doubtless, therefore, 

 Aldabra, in the same land-mass. In other words the whole 

 of the tortoise-islands of the Indian Ocean formerly consti- 

 tuted a portion of the African continent, just as the Galapagos 

 group was at about the same date united to the South 

 American mainland. 



This, however, is not all, for Dr. Standing is of opinion 

 that Africa (with which India was probably then connected) 

 formed during the early portion of the Tertiary period a centre 

 of dispersal, from which the ancestors of the South American 

 monkeys and marmosets reached their present home. And 

 it will be obvious that, if this theory be true, it will also 

 serve to explain in a perfectly simple and thoroughly satis- 

 factory manner the distribution and origin of the giant tortoises 

 of the Galapagos and the islands of the Indian Ocean. This 

 hypothesis will likewise account for the presence of species 

 with a peculiar type of cervical vertebrae in. localities so widely 

 sundered as Charles Island in the Galapagos group and 

 Aldabra in the Indian Ocean. 



There is, of course, the alternative supposition that the 

 giant tortoises of the Pacific and the Indian Ocean may have 

 reached their present habitation by way of a land-bridge 

 across Bering Strait, without travelling equatorially ; but, in 

 spite of anything I may have previously written to the con- 

 trary, I am now of opinion, in view of their comparatively 

 near relationship, that radiation from an African centre of 

 dispersal is the stronger and preferable explanation. 



Whether, however, the first or the second explanation be 

 accepted, it does not affect the opinion that all the modern 

 tortoise-islands are of continental, as distinct from oceanic, 

 origin ; and that in each instance the tortoise-population has 

 travelled overland from the adjacent continent, or rather that 

 it is a remnant of the population which originally occupied 

 each mainland (and, on the connection theory, the intermediate 

 land-bridge). 



