This last remark would be superfluous if, as was for a long time believed, the Paris Axolotls, of which the metamorphosis was first observed and which at the time made such a sensation, were actually _Siredon Mexicanus_, _i.e._ the _Siredon_ which alone in its native country bears the name of Axolotl. In his first communication Duméril was himself of this opinion; he then termed the animal “_Siredon Mexicanus vel Humboldtii_,”[229] but subsequently, in his amplified work[230] on the transformation of the Axolotl observed in the Jardin des Plantes, he retracted this view, and after a critical comparison of the five described species of _Siredon_, he came to the conclusion that the species in the possession of the Paris Museum was probably _Siredon Lichenoides_ (Baird). All the transformations of Axolotls observed in Europe must consequently be referred to this species, since they were--at least as far as I know--all derived from the Paris colony. My own experimental specimens were also indirectly descended from these. Now it must be admitted that this does not coincide with the fact that the Amblystoma form which Duméril first obtained from his Axolotls agreed with Cope’s species, _A. Tigrinum_, while on the other hand we learn from Marsh[231] that _Siredon Lichenoides_ (Baird), when it does undergo metamorphosis, becomes transformed into _Amblystoma Mavortium_ (Baird). Marsh found _Siredon Lichenoides_ in mountain lakes (7000 feet above the sea) in the southwest of the United States (Wyoming Territory), and obtained from them, by breeding in aquaria, _Amblystoma Mavortium_ (Baird). He considers it indeed doubtful whether the Amphibian undergoes this transformation in its native habitat, although he certainly states this opinion without rigorous proof on purely theoretical considerations, because, according to his view, “the low temperature is there less favourable.”[232] If I throw doubt upon this last statement it is simply because _Amblystoma Mavortium_ is found native in many parts of the United States, viz:--in California, New Mexico, Texas, Kansas, Nebraska, and Minnesota. It is indeed by no means inconceivable that in the mountain lakes where Marsh obtained this species, it may behave differently with respect to metamorphosis than in other habitats, and this appears probable from certain observations upon _Triton_ which will be subsequently referred to.