at each 'revolution'
taking place on the earth's surface, the whole batch of plants and
animals was swept out of existence, and the world was restocked with a
'new creation,' why should the brand-new forms, at any particular
locality, have such a 'ghost-like' resemblance to those that had gone
before? It is interesting to note that, just at the same time, a similar
discovery was made with respect to Australia. In caves in that country,
a number of bones were found which, though evidently belonging to
'extinct' animals, yet must have belonged to forms resembling the
kangaroos and other 'pouched animals' (marsupials) now so distinctive of
that continent. But of this fact Darwin was not aware until after his
return to England in 1836.

Among the objects sent from home, which awaited Darwin on his return to
Monte Video, was the second volume of Lyell's _Principles_, then newly
published; this book, while rejecting Lamarckism, was crowded with facts
and observations concerning variation, hybridism, the struggle for
existence, and many other questions bearing on the great problem of the
origin of species. I think there can be no doubt that from this time
Darwin came to regard the question of species with an interest he had
never felt before.

It is of course not suggested that, at this early date, Darwin had
formed any definite ideas as to the _mode_ in which new species might
possibly arise from pre-existing ones or even that he had been converted
to a belief in evolution. Indeed in 1877 he wrote 'When I was on board
the _Beagle_ I believed in the permanence of species' yet he adds 'but
as far as I can remember _vague doubts_ occasionally flitted across my
mind.' Such 'vague doubts' could scarcely have failed to have arisen
when, as happened during all his journeys from north to south of the
South American Continent, he found the same curious correspondence
between existing and late fossil forms of life again and again
illustrated.

But towards the end of the voyage, an even stronger element of doubt as
to the immutability of species was awakened in his mind. When he came to
study the forms of life existing in the Galapagos Islands, off the west
coast of South America, he was startled by the discovery of the
following facts. Each small island had its own 'fauna' or assemblage of
animals--this being very strikingly shown in the case of the reptiles
and birds. And yet, though the _species_ were different, there was
obvious