4684 THE ZooLocisT—NoOVEMBER, 1875. 
allied species, however distant in their habitats, will account for 
the occurrence of the tortoises in the Galapagos and Mascarenes 
in the same way as, for instance, for the distribution of the tapirs, 
viz., by the hypothesis of changes of the surface of the globe. 
Taking into consideration other parts of the Faun, they would 
have to assume, in this case, a former continuity of land (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. Indeed, the 
terrestrial and freshwater Faune of Tropical America and Africa 
offer so many points of intimate relationship as to support very 
strongly such atheory. The tortoises, then, would be assumed to 
have been spread over the whole of this large area, without being 
able to survive long the arrival of man or large carnivorous 
mammals. The former, especially before he had provided himself 
with missile weapons, would have eagerly sought 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 became separated from the mainland before 
their enemies followed them. With this hypothesis we should be 
obliged to contend for this animal type an age extending over 
enormous periods of time, of which the period required for the loss 
of power of flight in the dodo or solitaire is but a fraction. 
To my mind the advocacy of an independent origin of the same 
animal type, however highly organized, in different localities, seems 
equally justified. It has been urged that closely similar structures 
of the animal organism have been developed without generic rela- 
tionship; so, also, the same complex organic compound, as sugar, 
is produced normally by the plant and abnormally by the human 
organism. Without overstepping too far the limits of probability, 
we may assume that some land tortoises were carried by stream 
and current from the American Continent to the Galapagos, and 
that others from Madagascar or Africa, found in a similar manner 
a new home in the Mascarene Islands. These tortoises may 
originally have differed from each other, like the Testudo tabulata, 
radiata, sulcata, of our days, possibly not exceeding these species 
in size, but being placed under the same external physical con- 
ditions evidently most favourable for their further development, 
they assumed in course of time the same gigantic proportions and 
