19. Fertilisation is internal, and is effected, with the single exception of Sphenodon, by means of male copulatory organs.
20. An amnion and an allantois are formed during development.
Numbers 1, 2, 6, 7, 8, 14, 16, 18, 20 separate the Reptiles from the Amphibia. Cf. also pp. [4] and [5].
Numbers 9 (b), 10, 12, and 13 separate them from the Birds and Mammals.
Numbers 3, 8, and 11 separate them from the Mammals.
The evolution of the classification of the Reptiles has to a certain extent been already treated on pp. [7]-[9]. For a long time only Chelonia or Tortoises, Ophidia or Snakes, and Saurii were recognised as their principal divisions. Then the Crocodiles were separated from the Lizards; later the Coeciliae were removed from the Snakes and referred to the Amphibia, and ultimately Sphenodon was recognised as deserving a separate position, equal in rank to the other groups. Stannius showed that the Crocodiles and Tortoises are relatively near allies in opposition to the likewise closely allied Lizards and Snakes (Sphenodon was then unknown), and he expressed this by the term Monimostylica, or creatures with fixed quadrate bones, for the former, and Streptostylica, creatures with movable quadrates, for the latter combination. The fossil Reptiles were hardly allowed proper places in the system. In various zoological text-books they were, or are even now, treated as inconvenient, outlying, or supernumerary members. A long time elapsed before, thanks to the labours of H. von Meyer, Owen, Huxley, Marsh, Cope, Zittel, and Seeley, it was recognised that the extinct groups form the preponderant mass of Reptiles, and that it is the recent groups which, in spite of the bewildering number of species of Lizards and Snakes, are the comparatively few and much-reduced members of a once flourishing class. With the exception of the Lizards and Snakes, which are on the ascending branch, the modern Sphenodon, the Crocodiles and the Tortoises are a mere fraction, comprising a few survivals of richly-developed groups, while all the others, the overwhelming majority, have died out.
The classification adopted in this volume is as follows:–
Class Reptilia.
Sub-Class IIIII. Proreptilia.
Sub-"ClasIII II. Prosauria. Orders: Microsauri, Prosauri.