It now only remains questionable whether _each larva_ could have been forced to undergo metamorphosis, but this could only be decided by new experiments. It was originally my intention to have delayed the publication of the experiments till Fräulein v. Chauvin had repeated them in larger numbers, but as my Axolotls have not bred this year (1875) I must abandon my scheme, and this can be done the more readily because, for the theoretical consideration of the facts, it is immaterial whether _all_ or only _nearly all_ the Axolotls could have been compelled to undergo transformation. I must not, however, omit to mention that Herr Gehrig, the curator of our Zoological Museum, bred a considerable number of larvæ from the same brood as that with which Fräulein v. Chauvin experimented, and that of these larvæ six lived over the winter _without undergoing metamorphosis_. They were always kept in deep water and thus furnished the converse experiment to those recorded above; they further prove that this whole brood did not have a previous tendency to undergo metamorphosis. If these new facts are to be made use of to explain the nature of this extraordinary process of transformation in accordance with our present conception, the data already known must in the first place be called to our aid. It has first to be established that _Siredon Mexicanus_ never, as far as we know, undergoes metamorphosis in its native country. This Amphibian is there only known in the _Siredon_ form, a statement which I have taken from De Saussure,[225] who has himself observed the Axolotl in the Mexican lakes. This naturalist never found a single Amblystoma in the neighbourhood of the lakes, “nevertheless the larva (Axolotl) is so common there that it is brought into the market by thousands.” De Saussure believes that in Mexico the Axolotl does not undergo transformation.[226] The same statement is distinctly made by Cope,[227] whose specimens of _Siredon Mexicanus_ bred in America, even in captivity showed “no tendency to become metamorphosed.” On the other hand Tegetmeier observed[228] that one out of five specimens obtained from the Lake of Mexico underwent metamorphosis, and this accordingly establishes the second fact, viz. that the true Axolotl becomes transformed under certain conditions into an Amblystoma when in captivity.