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 peculiarity 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 variability already mentioned. 
In addition to the giant tortoises, the Galapagos 
possess both lizards and snakes. Two of the lizards 
are very large and of very peculiar habits. One (Cono- 
lophus subcristatus) 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 
lizards is quite similar to that of the tortoises, it would 
seem that originally the lizards inhabited the arid 
ground, and the tortoises the damp upper regions, but 
each has become partially adapted to the territory of 
the other. The lizards reach a length of a yard, and 
