(Metopias) as between the existing stag of Europe and the wapiti deer. Which branch of these primordial amphibians gave rise to the modern frogs and salamanders we do not know. This and hundreds of similar facts suggest the vital importance of paleogeography.
As regards paleogeography, the great induction can be made that, throughout the whole period of vertebrate evolution and until comparatively recent times, Europe, Asia and North America constituted one continent and one life region, or Arctogæa (Huxley 1868, Blanford 1890), with which the continents of the southern hemisphere, namely, Africa, South America and Australia, were intermittently, but not continuously connected by land. A great southerly continent, Notogæa (Huxley 1868), connected with a south polar Antarctica, now submerged, is a theory very widely supported by zoologists and, I believe, by botanists, although its existence is still denied by certain geographers (Murray). We find Permian, Jurassic, late Cretaceous and early Tertiary proofs of Antarctica in the fresh-water crustaceans (Ortmann), in fresh-water fishes (Gill), in littoral mollusca (Ortmann), in reptiles (Smith Woodward and Osborn), in birds (Forbes and Milne Edwards), in worms (Beddard), in the Australian animals (Spencer), in the fossil mollusca of Patagonia (Ortmann) and in the fossil mammals of Patagonia (Ameghino). To marshal and critically examine all this evidence and convert this most convenient Antarctic hypothesis into an established working theory I consider one of the most pressing problems of the day.
Problem of the Source of the Reptiles and Mammals.
Returning from this geographical detour to paleontology as history, we should first note that already in the Permian there was developed such an astonishing variety and differentiation of the reptiles that we must look to future discoveries in the Carboniferous to find the actual points of descent of reptiles from the amphibia. These Permian and Lower Triassic reptiles are of three kinds, comparable to a parent (Cotylosauria) and two offspring (Anomodontia and Diaptosauria). In the parent group (the Cotylosauria, or solid-skulled reptiles,) we find so many fundamental similarities to the Stegocephalia, or solid-skulled amphibia, that only by the possession of many parts of the body can we surely ditinguish reptile from amphibian remains. The primordial reptile was probably altogether a land animal continuously using its limbs in awkward progression, bringing forth its young by land-laid eggs and probably possessing gills only as vestiges. These cotylosaurs show very wide geographical distribution, South Africa, Siberia, Great Britain and North America, and equally remarkable adaptive radiations of habit into small and large, horned and hornless types, some of which were certainly dying out branches, while others led into the two offspring groups.
