which remained Axolotls were prevented from becoming perfect Amblystomas on account of these lakes, after the disappearance of the surrounding forests, having receded from their former boundaries, which are now covered with a saline, uninhabitable crust. This may be an explanation, although Axolotls do not live in brackish water. But Weismann went farther, and with his well-known dialectic powers has succeeded in spreading the belief not only that the Axolotl is a case of reversion to an ancestral stage, but that the present _Amblystoma_, instead of being the progressive, perfect form, is likewise a case of reversion. A reversion from a reversion! The whole line of evolution would then be as follows: _Amblystoma_; its young, owing to adverse circumstances, revert to the stage of the Perennibranchiate ancestors of all Urodela; if some of these Axolotls lose their gills and fins, they revert thereby into the original _Amblystoma_. {115}Surely a roundabout way of explaining a curious but after all rather simple process of Neoteny; cf. p. 63. Observations on the metamorphosis of _Siredon lichenoides_ into _Amblystoma mavortium_ have been made by Marsh, who also gives figures of the larval and adult forms.[57] SUB-FAM. 4. SALAMANDRINAE.–The six genera of this subfamily fall into two natural groups: I, True Salamanders, with the palatal teeth arranged in a pair of S-shaped figures, and without a fronto-squamosal arch. II, Tritons, with the palatal teeth in the shape of a Λ, _i.e._ the right and left series meet at an angle; the fronto-squamosal arch is present, either bony, or at least ligamentous. _Triton cristatus_ is, however, exceptional, in that the two palatal series often do not meet and that the arch is absent. The number of fingers is universally four, that of the toes is five except in _Salamandrina_, which has only four. The geographical distribution of the sub-family, entirely Periarctic, may be said to be the reverse of that of the Amblystomatinae. Of the twenty-five species namely, only two are American, four are Eastern Asiatic, and of the remaining nineteen, two are Algerian, while the rest live in Europe or in Asia Minor. It is in fact an essentially Palaearctic group. The six genera can be distinguished as follows:– I. The palatal teeth are arranged in two S-shaped curves. True Salamanders. Tongue short and thick. _Salamandra_, p. 115. Tongue long and projectile. _Chioglossa_, p. 121. II. The palatal teeth are arranged in a Λ shape. True Tritons. With only four toes. _Salamandrina_, p. 122. With five toes. Pterygoids separated from the maxillary and quadrate bones: _Triton_, p. 122. Pterygoids touching the maxillae and quadrates. Himalo-Chinese: _Tylototriton_, p. 132. Pterygoids united broadly with the maxillae. Chinese: _Pachytriton_, p. 132. _Salamandra._–Without fronto-squamosal arch. Five toes. Tail round. Three species in Europe and Western Asia.