most of the islands from each other. In "My Life" some interesting
tables are given to illustrate how the two streams of immigration
entered these islands, and further that "as its geological structure
shows ... Timor is the older island and received immigrants from
Australia at a period when, probably, Lombok and Flores had not come
into existence or were unhabitable.... We can," he says, "feel confident
that Timor has not been connected with Australia, because it has none of
the peculiar Australian mammalia, and also because many of the commonest
and most widespread groups of Australian birds are entirely wanting."[2]

Two other papers, dealing with parrots and pigeons respectively
(1864-5), were thought by Wallace himself to be among the most important
of his studies of geographical distribution. Writing of them he says:
"These peculiarities of distribution and coloration in two such very
diverse groups of birds interested me greatly, and I endeavoured to
explain them in accordance with the laws of Natural Selection."

In March, 1864, having begun to make a special study of his collection
of butterflies, he prepared a paper for the Linnean Society on "The
Malayan Papilionidæ, as illustrating the Theory of Natural Selection."
The introductory portion of this paper appeared in the first edition of
his volume entitled "Contributions to the Theory of Natural Selection"
(1870), but it was omitted in later editions as being too technical for
the general reader. From certain remarks found here and there, both in
"My Life" and other works, butterflies would appear to have had a
special charm and attraction for Wallace. Their varied and gorgeous
colourings were a ceaseless delight to his eye, and when describing them
one feels the sense of pleasure which this gave him, together with the
recollection of the far-off haunts in which he had first discovered
them.