ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 371 



Cliloride and carbonate of soda, chiefly, are dissolved iu the water in so 

 sensible a quantity tliat they are regularly precipitated as a crnst on the 

 shore of the lake, and this crnst is gathered there during the dry sea- 

 son and comes into the market under the name of tequisquite. 



So, therefore, there is no lack of points of support for the conjecture 

 that peculiar circumstances made life on the land more difficult to the 

 animal than life iu the water, and this alone might have been sufficient 

 to bring it back to the habit of water-life only, and with that also to the 

 reversion into the Perennibranchiate or Ichthyodea form. 



Yet a truce to conjectures. We cannot lament that from the great dis- 

 tance and lapse of time, we are not in the condition to ascertain with 

 definiteness the causes which compelled the Axolotl to give up the 

 Amblystoma stage, so long as we are not able to solve the case of rever- 

 sion that lies much nearer to us in the Tritons of Filippi and Jullien. 

 Yet here, also, universal causes affecting the whole colony of Tritons 

 must have been at the foundation, since, at least in Filippi's case, the 

 great majority of the Individuals remained in the larva state. It must 

 be that experiments with Triton larvte would bring greater clearness 

 here; they would have to determine, before all else, whether the rever- 

 sion can be called forth artificially, and, if this is the case, through what 

 inflaences. 



According to the above-quoted experiences with butterflies, as well 

 as according to the results attained with Axolotls, we should have to 

 expect with the Tritons that the reversion to the Ichthyode form would 

 occur if one would continue the stimulus of the water bathing the gills 

 and the whole body, and at the same time would take away the stimu- 

 lus under whose operation the Salamandrida form has been fashioned — 

 the stimulus of the air bathing the gills, the skin, and the lungs. I 

 hope at a later time to be able to report on experiments of this kind.* 



^o one will wish to object to my hypothesis of reversion, that on one 

 side it opposes what it of itself postulates on the other side : a sudden 

 change of structure. The characteristic of the reversion is precisely iu 

 reaching at a bound an older, that is, an earlier existing phyletic stage. 

 That this occurs is a fact ; while the reaching at a bound, to express 

 myself figuratively, of an aim (pardon the word) that lies forward has 

 never yet been proved or even made probable. 



But as we succeeded in finding in the Axolotl's present conditions of 

 life-forces which make its life on the land difficult or quite impossible, 

 and therefore show a motive for that return to the Ichthyodea form 

 which seems to have taken place ; so can the other side of my hypothesis 



*At any rate, Schreibers seems, iu his eesay already cited above, to have communi- 

 cated experiments from which it follows, as Leydig recapitulates them in the place 

 referred to, that the last change, i. e., the loss of the gills, " may be delayed by forcible 

 means." To be sure, it does not follow from this that the animals of the experiment 

 also became sexually mature at the same time. Unfortunately I could not myself ex- 

 amine the paper, as the volume of the Iris for 1833, as referred to, contains nothiag 

 of the kind, and I have lived for a long time at a distance from any large library. 



