148 SPECIAL FEATURES 



the western Indian Ocean, and in the Galapagos archi- 

 pelago. In addition to their large size the animals have 

 as special peculiarities the fact that they show much 

 individual variation, and tend also to split up into 

 species, different species occurring on adjacent islands. 

 No small tortoises occur on the islands containing these 

 large forms. A final pecuUarity is that the bony cara- 

 pace tends to be reduced in thickness, perhaps because 

 till man came the animals had few enemies. The diet 

 is exclusively vegetarian, and the animals occur in both 

 the upper well-watered region and in the lower arid 

 region. The fact, however, that they drink greedily, 

 and are fond of wallowing in muddy water, suggests 

 that they are not native to arid regions. Darwin gives 

 an interesting description of the long journeys made by 

 the low-ground tortoises to the springs of the upper 

 region, in order to obtain water. The cactuses of the 

 arid regions form a favourite food plant. The exact 

 number of species is a matter of doubt, owing to the 

 individual variabihty already mentioned. 



In addition to the giant tortoises, the Galapagos 

 possess both Kzards and snakes. Two of the lizards 

 are very large and of very peculiar habits. One (fiono- 

 lophus svhcristatus) is found only on the central islands 

 of the archipelago, and occurs both in the upper and 

 lower regions, but more abundantly in the latter. The 

 forms from the arid districts, however, do not travel 

 upwards to the springs to drink, and are far more 

 numerous than the upland forms. As the diet of these 

 Uzards is quite similar to that of the tortoises, it would 

 seem that originally the hzards inhabited the arid 

 ground, and the tortoises the damp upper regions, but 

 each has become partially adapted to the territory of 

 the other. The hzards reach a length of a yard, and 



