312 SCIENCE PROGRESS 



Africa in the palmy days of its animal inhabitants. Moreover, 

 the Egyptian Eocene species, Testiido amnion, which was pro- 

 bably one of the earliest representativ'^es of the entire group, 

 lived in company with the gigantic horned ungulate Arsinoi- 

 therium, huge hyraxes, the ancestors of the modern elephants, 

 and primitive carnivora as large as, if not larger than, wolves. 

 Giant continental tortoises lived therefore throughout the whole 

 of their known range in time in company with big mammals, 

 including, during the Siwalik period, a tiger or lion fully equal 

 in size to the existing species. 



Of course it may be argued that the Siwalik tiger or lion, 

 which was a larger and more powerful carnivore than any of 

 the primitive species associated with the Egyptian Eocene Tcstiido 

 ammon, may have killed off the gigantic contemporary tortoises, 

 and that other big cat-like carnivora did the same for the other 

 continental species. But it is inconceivable that such mail-clad 

 reptiles, which could withdraw their heads with lightning-like 

 rapidity into the shelter of their bucklers, could have been 

 harmed in even the slightest degree by the biggest and most 

 powerful carnivore that ever walked this earth. If, however, 

 giant tortoises are safe from open attack by carnivorous mammals, 

 it by no means follows that they are immune to the insidious 

 operations of bacteria and trypanosomes ; and in the absence of 

 any other conceivable reason for their extinction it is possible, 

 if not indeed probable, that their disappearance from the con- 

 tinental areas may be due to one or other of those minute but 

 deadly organisms. It is true that it is somewhat difficult to 

 understand how such diminutive enemies should have driven 

 their attack home almost simultaneously throughout the world ; 

 but this is a difficulty which would occur in the case of every 

 exterminating agent. It may be added that many naturalists 

 now attribute the extinction of numerous groups of big animals, 

 such as the ground-sloths of South America, to the attacks of 

 parasites. 



Whatever may have been the nature of the agency to which 

 the old giant tortoises of the continents eventually succumbed, 

 it is perfectly evident that their modern insular representatives, 

 or rather the ancestors of the same, must have reached their 

 habitats from the adjacent continents ; this having been 

 admitted by Dr. Giinther in the case of the species of the 

 Galapagos long before any extinct American members of the 



