Moreover, it is hardly permissible to seek such an explanation, since Urodela are known which have no gills in the adult state, and which nevertheless possess all the other characters of the _Ichthyodea_, viz. want of eyelids, characteristic palatine teeth, and the tongue bone. This is the case with the genera _Amphiuma_ (Linn.), _Menopoma_ (Harl.), and _Cryptobranchus_ (v. d. Hoev.). The two first genera, as is known, still possess gill-clefts, but _Cryptobranchus_ has even lost these clefts, which, as in _Amblystoma_, are overgrown by skin; nevertheless _Cryptobranchus_ is, according to the concurrent testimony of all systematists, a true salamander in habits, tongue bone, palatine teeth,[241] &c. It must further be added that the Axolotl itself can lose the gills without thereby becoming transformed into an Amblystoma. I have previously mentioned that in Axolotls which were kept in shallow water the gills frequently became diminutive, and it also sometimes happens that they completely shrivel up. I possess an Axolotl preserved in alcohol in which the gills have shrivelled up into small irregular bunches, and the dorsal crest is also so completely absent that its place is occupied by a long furrow, and even on the tail the crest has entirely disappeared from the lower edge and about half from the upper edge. Notwithstanding this, the creature is widely removed from Amblystoma in structure; it possesses the arched branchial apparatus, the palatine teeth, the skin, &c., of the Axolotl. These facts prove, therefore, that the shedding of the gills by no means always entails all the other modifications which we observe in the metamorphosis of Axolotl, so that these modifications are thus not by any means the necessary and immediate consequence of such gill shedding. Whether these modifications will occur after a long series of generations--whether the successors of _Cryptobranchus_ will also one day acquire the salamandriform structure is another question, and one which I could not exactly answer in the negative. But this question does not here come into consideration, as we are now only concerned with the _immediate result_ of the shedding of the gills. The problem appears therefore to be as follows:--Either the hitherto received interpretation of the transformational history of the Axolotl as a further development of the species is incorrect, or else the case of Axolotl incontestably proves the existence of a phyletic vital force. We have now to ask whether the facts of this transformational history are not capable of another explanation. I believe that this is certainly possible, and that another interpretation can be shown to be correct with some degree of probability.