INTRODUCTION. 
9 
now being partly genetic, partly adaptive. To test (if test it can be called) this hypo- 
thesis, I compared our Tortoises with those of the neighbouring continents, but did not 
succeed in finding any evidence in their osseous frame which might be used as 
argument in favour of such direct genetic relationship. In none have I found the 
singular modification of the articulations of the nuchal vertebrae of the Aldabra 
Tortoise. 
The naturalists who maintain a common origin for allied species, however distant in 
their habitats, will have to assume a former continuity of land (extending over 150° of 
longitude, but probably varying in extent, and interrupted at various periods) between 
the Mascarenes and Africa, between Africa and South America, and, finally, between 
South America and the Galapagos. A continuity of land in this direction is more 
probable than one in the opposite hemisphere, which would extend over 210°. Indeed 
the terrestrial and freshwater faunae of Tropical America and Africa off"er so many 
points of intimate relationship as very strongly to support such a theory. The Tor- 
toises, then, would be assumed to have been spread across the whole of this large area, 
without being able long to survive the arrival of man or large carnivorous mammals. 
The former, especially before he had provided himself with missile weapons, would 
eagerly seek for them, as they were the easiest of his captures, yielding a most 
plentiful supply of food ; consequently they were exterminated on the continents, only 
some remnants being saved by having retired into places which, by submergence, be- 
came separated from the mainland before their enemies followed them. The discovery 
of bones of Tortoises in Malta, which seem to be almost identical with the corre- 
sponding parts in Galapagos Tortoises, as stated in a paper read before the Geological 
Society only a short time ago by Dr. Leith Adams, clearly proves the much greater 
extension of this Chelonian type at a former geological epoch. 
c 
