geographical and physical changes on which the present insect-distribution depends.1 ...

"In a day or two I leave for Timor, where, if I am lucky in finding a good locality, I expect some fine and interesting insects."

I reached Delli, the chief place in the Portuguese part of the island, on January 12, 1861, and stayed there about three months and a half. I lived with an Englishman, Captain Hart, who had a coffee plantation about a mile out of the town; and there was also another Englishman, Mr. Geach, a mining engineer, who had come out to open copper mines for the Portuguese Government, but as no copper ore could be found, he was waiting for an opportunity to return to Singapore. They were both very pleasant people, and I enjoyed myself while there, though the collecting was but poor, owing to the excessive aridity of the climate and the absence of forests. I obtained, however, some rare birds and a few very rare and beautiful butterflies by the side of a stream in a little rocky valley shaded by a few fine trees and bushes. Of beetles, however, there were absolutely none worth collecting.

Leaving Timor at the end of April, I went by the Dutch mail steamer to Cajeli in Bouru, the last of the Molucca Islands which I visited. Here I stayed two months, but was again disappointed, since the country was almost as unproductive as Ceram. For miles round the town there were only low hills covered with coarse grass and scattered trees, less productive of insects than a bare moor in England. Some patches of wood here and there and the fruit trees around the town produced a few birds of peculiar species. I went to a place about twenty miles off, where there was some forest, and remained there most of my time; but insects were still very scarce, and birds almost equally so. I obtained, however, about a dozen quite new species of birds and others which were very rare, together with a small collection of beetles; and then, about the end of June, took the mail

1 These ideas were thoroughly worked out in my book on "The Geographical Distribution of Animals," published in 1876.

steamer by Ternate and Menado to Sourabaya, the chief town in eastern Java.

I stayed here about a month, spending most of the time at the foot of the celebrated mount Arjuna; but the season was too dry, and both birds and insects very scarce. I therefore went on to Batavia and thence to Buitenzorg and to the Pangerango mountain, over ten thousand feet high. At a station about four thousand feet above sea-level, where the main road passes through some virgin forest, I stayed some weeks, and made a tolerable collection of birds and butterflies, though the season was here as much too wet as East Java was too dry. I next went to Palembang in Sumatra, which I reached by way of Banka on November 8. Here the country was mostly flooded, and I had to go up the river some distance to where a military road starts for the interior and across the mountains to Bencoolen. On this road, about seventy miles from Palembang, I came to a place called Lobo Raman, surrounded with some fine virgin forest and near the centre of East Sumatra. Here, and at another station on the road, I stayed about a month, and obtained a few very interesting birds and butterflies; but it was the height of the wet season, and all insects were scarce. I therefore returned to Palembang and Banka, and thence to Singapore, on my way home. While waiting here for the mail steamer, two living specimens of the smaller paradise bird (Paradisea papuana) were brought to Singapore by a trader, and I went to see them. They were in a large cage about five or six feet square, and seemed in good health, but the price asked for them was enormous, as they are so seldom brought, and the rich Chinese merchants or rich natives in Calcutta are always ready to purchase them. As they had never been seen alive in Europe I determined to take the risk and at once secured them, and with some difficulty succeeded in bringing them home in safety, where they lived in the Zoological Gardens for one and two years respectively.

While living in the wilds of Sumatra I wrote two letters, to my friends Bates and Silk, which, being the last I wrote before reaching home, may be of interest as showing what

subjects were then uppermost in my mind. The first from which I will quote is that to Mr. Bates, and referring to a paper on the Papilios of the Amazon which he had sent me I make some remarks on the distribution of animals in South America, which I do not think I have published anywhere.

"Your paper is in every respect an admirable one, and proves the necessity of minute and exact observation over a wide extent of country to enable a man to grapple with the more difficult groups, unravel their synonymy, and mark out the limits of the several species and varieties. All this you have done, and have, besides, established a very interesting fact in zoological geography, that of the southern bank of the lower river having received its fauna from Guayana, and not from Brazil. There is, however, another fact, I think, of equal interest and importance which you have barely touched upon, and yet I think your own materials in this very paper establish it, viz. that the river, in a great many cases, limits the range of species or of well-marked varieties. This fact I considered was proved by the imperfect materials I brought home, both as regards the Amazon and Rio Negro. In a paper I read on 'The Monkeys of the Lower Amazon and Rio Negro' I showed that the species were often different on the opposite sides of the river. Guayana species came up to the east bank, Columbian species to the west bank, and I stated that it was therefore important that travellers collecting on the banks of large rivers should note from which side every specimen came. Upon this Dr. Gray came down upon me with a regular floorer. 'Why,' said he, 'we have specimens collected by Mr. Wallace himself marked "Rio Negro" only.' I do not think I answered him properly at the time, that those specimens were sent from Barra before I had the slightest idea myself that the species were different on the two banks. In mammals the fact was not so much to be wondered at, but few persons would credit that it would apply also to birds and winged insects. Yet I am convinced it does, and I only regret that I had not collected and studied birds there with the same assiduity as I

have here, as I am sure they would furnish some most interesting results. Now, it seems to me that a person having no special knowledge of the district would have no idea from your paper that the species did not in almost every instance occur on both banks of the river. In only one case do you specially mention a species being found only on the north bank. In other cases, except where the insect is local and confined to one small district, no one can tell whether they occur on one or both banks. Obydos you only mention once, Barra and the Tunantins not at all. I think a list of the species or varieties occurring on the south bank or north bank only should have been given, and would be of much interest as establishing the fact that large rivers do act as limits in determining the range of species. From the localities you give, it appears that of the sixteen species of papilio peculiar to the Amazon, fourteen occur only on the south bank; also, that the Guayana species all pass to the south bank. These facts I have picked out. They are not stated by you. It would seem, therefore, that Guayana forms, having once crossed the river, have a great tendency to become modified, and then never recross. Why the Brazilian species should not first have taken possession of their own side of the river is a mystery.

I should be inclined to think that the present river bed is comparatively new, and that the southern lowlands were once continuous with Guayana; in fact, that Guayana is older than north Brazil, and that after it had pushed out its alluvial plains into what is now north Brazil, an elevation on the Brazilian side made the river cut a new channel to the northward, leaving the Guayana species isolated, exposed to competition with a new set of species from further south, and so becoming modified, as we now find them. . . . The whole district is, I fear, too little known geologically to test this supposition. The mountains of north Brazil are, however, said to be of the cretaceous period, and if so their elevation must have occurred in tertiary times, and may have continued to a comparatively recent period. Now if there are no proofs of such recent upheaval in the southern mountains of Guayana, the theory

would thus far receive support. I regret that your time was not more equally divided between the north and south banks, but I suppose you found the south so much more productive in new and fine things. . . .

"I am here making what I intend to be my last collections, but am doing very little in insects, as it is the wet season and all seems dead. I find in those districts where the seasons are strongly contrasted the good collecting time is very limited-only about a month or two at the beginning of the dry, and a few weeks at the commencement of the rains. It is now two years since I have been able to get any beetles, owing to bad localities and bad weather, so I am becoming disgusted. When I do find a good place it is generally very good, but such are dreadfully scarce. In Java I had to go forty miles in the eastern part and sixty miles in the western to reach a bit of forest, and then I got scarcely anything. Here I had to come a hundred miles inland, by Palembang, and though in the very centre of Eastern Sumatra, the forest is only in patches, and it is the height of the rains, so I get nothing. A longicorn is a rarity, and I suppose I shall not have as many species in two months as I have obtained in three or four days in a really good locality. I am getting, however, some sweet little blue butterflies (Lycanida), which is the only thing that keeps up my spirits."

The letter to my friend Silk will be, perhaps, a little more amusing, and perhaps not less instructive.

"Lobo Roman, Sumatra, December 22, 1861.

"MY DEAR GEORGE,

"Between eight and nine years ago, when we were concocting that absurd book, 'Travels on the Amazon and Rio Negro,' you gave me this identical piece of waste paper with sundry others, and now having scribbled away my last sheet of 'hot-pressed writing,' and being just sixty miles from another, I send you back your gift, with interest; so you see that a good action, sooner or later, find its sure reward.