terrestrial life
contained in them, one of these may have been related to another as New
Zealand is to Australia, or as Australia is to India, at the present day.
Analogy seems to me to be rather in favour of, than against, the
supposition that while only 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 Arc