We find two species of Eupetes, a curious Malayan genus allied to the forked-tail water-chats; two of Alcippe, an Indian and Malay wren-like form; an Arachnothera, quite resembling the spider-catching honeysuckers of Malacca; two species of Gracula, the Mynahs of India; and a curious little black Prionochilus, a saw-billed fruit pecker, undoubtedly allied to the Malayan form, although perhaps a distinct genus.

Now not one of these birds, or anything allied to them, occurs in the Moluccas, or (with one exception) in Celebes or Australia; and as they are most of them birds of short flight, it is very difficult to conceive how or when they could have crossed the space of more than a thousand miles, which now separates them from their nearest allies.

Such facts point to changes of land and sea on a large scale, and at a rate which, measured by the time required for a change of species, must be termed rapid.
By speculating on such changes, we may easily see how partial waves of immigration may have entered New Guinea, and how all trace of their passage may have been obliterated by the subsequent disappearance of the intervening land.
There is nothing that the study of geology teaches us that is more certain or more impressive than the extreme instability of the earth's surface.

Everywhere beneath our feet we find proofs that what is land has been sea, and that where oceans now spread out has once been land; and that this change from sea to land, and from land to sea, has taken place, not once or twice only, but again and again, during countless ages of past time.

Now the study of the distribution of animal life upon the present surface of the earth, causes us to look upon this constant interchange of land and sea--this making and unmaking of continents, this elevation and disappearance of islands--as a potent reality, which has always and everywhere been in progress, and has been the main agent in determining the manner in which living things are now grouped and scattered over the earth's surface.