214 GIANT TORTOISES. [CH. IV 



the struggle for existence was keener, is in all probability 

 to be referred to the same causes as the defenceless state 

 of the Dodo and other island birds. 



The island of Mauritius was also inhabited quite 

 recently by gigantic tortoises which are now without 

 exception extinct. Dr Gadow in a recent communication 

 upon the subject 1 distinguishes no less than six "forms' 5 

 of these. He uses the word " form ' because it seems 

 improbable that they have the full value of species ; and 

 yet names are given to them without any such prefix as 

 "forma " or " var" It is at least not usual for species of 

 the same genus and all these giants belong to Testudo, 

 just like those of the Galapagos to herd together in a 

 limited tract. Now five out of these six forms have 

 deposited their bones in one marsh ; so much confused 

 were they, owing no doubt partly to the fault of those 

 who fished them out, that in some cases the bones seem 

 to have entirely lost their mutual relations. Waiving 

 the question of species it is clear that great variability 

 reigned among these large and unpersecuted inhabitants 

 of the Mauritius their freedom from enemies being also 

 perhaps indicated by the thinness of the shells. It is 

 incorrect to make the general statement that great size is 

 characteristic of island tortoises only, because the giant 

 Colossochelys of India and some other forms flourished 

 under continental conditions. But among living or but 

 recently extinct tortoises large size seems to have been 

 only attainable on these favoured because restricted spots, 



1 Trans. Zool. Soc. Vol. xm. 



