Perhaps the most remarkable instance of a transformation produced by the influence of environment is that of the Mexican water-newt, Axolotl. When gradually accustomed to live on dry land, this creature usually throws off its gills, develops lungs, alters the shape of its tail, and takes on all the characteristics of a terrestrial instead of an aquatic reptile. This transformation does not take generations to accomplish—it happens in one individual in the course of a few weeks or months. When found in the terrestrial form, the Axolotl is called _Amblystoma tigrinum_, and is classed among the salamanders. Its progeny are then _Amblystomas_, and they do not naturally revert to the Axolotl type, although under certain circumstances the steps of this amazing transformation can be retraced. The Axolotl is not a larva in the ordinary sense of the word, for it is not an imperfect creature; it is sexually mature, and in most cases, in nature, probably never develops into an _Amblystoma_, nor do the progeny of the _Amblystomas_ begin as Axolotls. What we have here is probably, as Weismann plausibly suggests, a case of a species which has almost reached the stage of evolution from an aquatic into a terrestrial form, so that a sufficient impulse from its environment suffices to send it over the border. Internal forces have evidently prepared the way for the change, and the process does not in the least resemble the mechanical selection of suitable characters from a crowd of fortuitous variations.[97] The case of the Porto Santo rabbit may also be quoted in this connexion. In the year 1419 the young born of a tame Spanish rabbit were put ashore on the island of Porto Santo near Madeira. No rabbits then existed on the island. They have since increased enormously, and have quite changed their appearance. They have acquired a peculiar colour, are very small, rat-like in shape, have nocturnal habits, and are noted for their extreme wildness. They no longer pair with the European rabbit. The case was observed by Haeckel, who styled the new species _Lepus Huxleyi_.[98]