Ganoid fishes inhabited the fresh waters of our Devonian land, Amphibia and Reptilia, or even higher forms, may have existed, though we have not yet found them.  The earliest Carboniferous Amphibia now known, such as Anthracosaurus, are so highly specialised that I can by no means conceive that they have been developed out of piscine forms in the interval between the Devonian and the Carboniferous periods, considerable as that is.  And I take refuge in one of two alternatives:  either they existed in our own area during the Devonian epoch and we have simply not yet found them; or they formed part of the population of some other distributional province of that day, and only entered our area by migration at the end of the Devonian epoch.  Whether Reptilia and Mammalia existed along with them is to me, at present, a perfectly open question, which is just as likely to receive an affirmative as a negative answer from future inquirers.

Let me now gather together the threads of my argumentation into the form of a connected hypothetical view of the manner in which the distribution of living and extinct animals has been brought about.

I conceive that distinct provinces of the distribution of terrestrial life have existed since the earliest period at which that life is recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that the progress of modification of terrestrial forms is more rapid in areas of elevation than in areas of depression.  I take it to be certain that Labyrinthodont Amphibia existed in the distributional province which included the dry land depressed during the Carboniferous epoch; and I conceive that, in some other distributional provinces of that day, which remained in the condition of stationary or of increasing dry land, the various types of the terrestrial Sauropsida and of the Mammalia were gradually developing.

The Permian epoch marks the commencement of a new movement of upheaval in our area, which dry land existed in North America, Europe, Asia, and Africa, as it does now.  Into this great new continental area the Mammals, Birds, and Reptiles developed during the Palaeozoic epoch spread, and formed the great Triassic Arctogaeal province.  But, at the end of the Triassic period, the movement of depression recommenced in our area, though it was doubtless balanced by elevation elsewhere; modification and development, checked in the one province, went on in that “elsewhere”; and the chief forms of Mammals, Birds and Reptiles, as we know them, were evolved and peopled the Mesozoic continent.  I conceive Australia to have become separated from the continent as early as the end of the Triassic epoch, or not much later.  The Mesozoic continent must, I conceive, have lain to the east, about the shores of the North Pacific and Indian Oceans; and I am inclined to believe that it continued along the eastern side of the Pacific area to what is now the province of Austro-Columbia, the characteristic fauna of which is probably a remnant of the population of the latter part of this period.