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summary of the more important of them in the order in which they were written.

The first of these, read in January, 1863, at a meeting of the Zoological Society, was on my birds from Bouru, and was chiefly important as showing that this island was undoubtedly one of the Moluccan group, every bird found there which was not widely distributed being either identical with or closely allied to Moluccan species, while none had special affinities with Celebes. It was clear, then, that this island formed the most westerly outlier of the Moluccan group.

My next paper of importance, read before the same society in the following November, was on the birds of the chain of islands extending from Lombok to the great island of Timor. I gave a list of one hundred and eighty-six species of birds, of which twenty-nine were altogether new; but the special importance of the paper was that it enabled me to mark out precisely the boundary line between the Indian and Australian zoological regions, and to trace the derivation of the rather peculiar fauna of these islands, partly from Australia and partly from the Moluccas, but with a strong recent migration of Javanese species due to the very narrow straits separating most of the islands from each other. The following table will serve to illustrate this :

Species derived from Java ...
Species derived from Australia

Lombok.
34
7

Flores.
28
14

Timor.

17 36

This table shows how two streams of immigration have entered these islands, the one from Java diminishing in intensity as it passed on farther and farther to Timor; the other from Australia entering Timor and diminishing still more rapidly towards Lombok. This indicates, as its geological structure shows, that Timor is the older island and that it received immigrants from Australia at a period when, probably, Lombok and Flores had not come into existence or were uninhabitable. This is also indicated by the fact that the Australian immigrants have undergone greater modification than the Javan. If we compare the birds of the whole

chain of islands according as they are of Javan or Australian origin, we have the following results :

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We thus see that while the proportion of the birds derived from each source is almost exactly equal, about three-fourths of those from Java have remained unchanged, while threefourths of those from Australia have become so modified as to be very distinct species. This shows us how the distribution of birds can, when carefully studied, give us information as to the past history of the earth.

We can also feel confident that Timor has not been actually 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. And we are equally certain that Lombok and the islands further east have never been united to Bali and Java, because four Australian or papuan genera of parrots and cockatoos are found in them, but not in Java, as are several species of honeysuckers (Meliphagidæ), a family of birds confined to the Australian region. On the other hand, a large number of genera which extend over the whole of the true Malay islands, from Sumatra to Java, never pass the narrow straits into Lombok. Among these are the long-tail parrakeets (Palæornis), the barbets (Megalæmidæ), the weaver-birds (Ploceus), the ground starlings (Sturnopastor), several genera of woodpeckers, and an immense number of genera of flycatchers, tits, gapers, bulbuls, and other perching birds which abound everywhere in Borneo and Java.

Two other papers dealt with the parrots and the pigeons of the whole archipelago, and are among the most important of my studies of geographical distribution. That on parrots was written in 1864, and read at a meeting of the Zoological

Society in June. Although the Malay Archipelago as a whole is one of the richest countries in varied forms of the parrot tribe, that richness is almost wholly confined to its eastern or Australian portion, for while there are about seventy species between Celebes and the Solomon Islands, there are only five in the three large islands, Java, Borneo, and Sumatra, together with the Malay peninsula, while the Philippine Islands have twelve. This extreme richness of the Moluccas and New Guinea is also characteristic of the Pacific Islands and Australia, so that the Australian region, with its comparatively small area of land, contains nearly as many species of this tribe of birds as the rest of the globe, and considerably more than the vast area of tropical America, the next richest of all the regions.

No two groups of birds can well be more unlike in structure, form, and habits than parrots and pigeons, yet we find that the main features of the distribution of the former, as just described, are found also, though in a less marked degree, in the latter. The Australian region by itself contains threefourths as many pigeons as the whole of the rest of the globe; tropical America, the next richest, having only about half the number; while tropical Africa and Asia are as poor, comparatively, in this group as they are in parrots. Turping now to our special subject, the Malay Archipelago, we find that it contains about one hundred and twenty species of pigeons, of which more than two-thirds (about ninety species) belong to the eastern or Austro-Malayan portion of it, which portion thus contains considerably more species, and much more varied forms and colours, than the whole of South America, Mexico, and the West Indies, forming the next richest area on the globe.

But this is not the only feature in which the parrots and the pigeons resemble each other. Both have characteristic forms and colours, which prevail generally over the whole world. In parrots this may be said to be green, varying into yellow, grey, red, and more rarely blue, and, except for a lengthened tail, having rarely any special developments of plumage. In pigeons, soft ashy lilac or brown tints are

1

characteristic of the whole group, often with metallic reflections; while soft greens, and sometimes metallic greens, occur in the forest regions of tropical Africa and Asia, but rarely anything approaching to crests or other developments of plumage.

But as soon as we reach the Moluccas and New Guinea we find a new type of coloration appearing in both groups. Among the lories we find vivid red and crimson, sometimes with a remnant of green on the wings and tail, but often covering the whole plumage, varied with bands or patches of equally vivid blue or yellow, while the red sometimes deepens into a blackish-purple. Among the cockatoos we have pure whites and deep black, with highly developed crests, often of great beauty, so that in these two families we seem to depart altogether from the usual parrot type of coloration.

Still more remarkably is this the case with the pigeons. In the extensive genus of small fruit-pigeons (Ptilonopus) the usual ground colour is a clear soft green, variegated by blue, purple, or yellow breasts, and crowns of equally brilliant colours. Besides these, we have larger fruit-pigeons almost wholly cream white, while the very large ground pigeons of New Guinea possess flat vertical crests, which are unique in this order of birds. The wonderfully brilliant golden green Nicobar pigeon is probably a native of the AustroMalayan islands, and may have been carried westward by Malay traders, and have become naturalized on a few small islands,

These peculiarities of distribution and coloration in two such very diverse groups of birds interested me greatly, and I endeayoured to explain them in accordance with the laws of natural selection. In the paper on Pigeons (published in The Ibis of October, 1865) I suggest that the excessive development of both these groups in the Moluccas and the Papuan islands has been due primarily to the total absence of arboreal, carnivorous, or egg-destroying mammals, especially of the whole monkey tribe, which in all other tropical forest regions are exceedingly abundant, and are

very destructive to eggs and young birds. I also point out that there are here comparatively few other groups of fruiteating birds like the extensive families of chatterers, tanagers, and toucans of America, or the barbets, bulbuls, finches, starlings, and many other groups of India and Africa, while in all those countries monkeys, squirrels, and other arboreal mammals consume enormous quantities of fruits. It is clear, therefore, that in the Australian region, especially in the forest-clad portions of it, both parrots and pigeons have fewer enemies and fewer competitors for food than in other tropical regions, the result being that they have had freer scope for development in various directions leading to the production of forms and styles of colouring unknown elsewhere. It is also very suggestive that the only other country in which black pigeons and black parrots are found is Madagascar, an island where also there are neither monkeys nor squirrels, and where arboreal carnivora or fruit. eating birds are very scarce. The satisfactory solution of these curious facts of distribution gave me very great pleasure, and I am not aware that the conclusions I arrived at have been seriously objected to.

Before I had written these two papers I had begun the study of my collection of butterflies, and in March, 1864, I read before the Linnean Society a rather elaborate paper on “The Malayan Papilionidæ, as illustrating the Theory of Natural Selection." This was published in the Society's Transactions, vol. xxv., and was illustrated by fine coloured plates drawn by Professor Westwood. I reprinted the introductory portion of this paper in the first edition of my "Contributions to the Theory of Natural Selection” in 1870, but in later editions it was omitted, as being rather too technical for general readers, and not easily followed without the coloured plates. I will therefore give a short outline of its purport here.

I may state for the information of non-entomological readers that the Papilionidæ form one of the most extensive families of butterflies, and from their large size, elegant forms,

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