ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 359 



9. The posterior face of each vertebra is sh'ghtly hollowed out before 

 as after the trausformatiou, but the anterior face is less coucave in the 

 Amblystoma than in the Siredon (Dum:6ril). 



The details cited from Dumerll under 7 and 9 I have not so far been 

 able to confirm by personal examination, as I was not willing to kill any 

 of my living Amblystomas, only for the purpose of verifying the details 

 of a naturalist in whom perfect confidence may surely be reposed. In 

 like manner, I have not yet seen the change in the arches of the gills. 

 All the other data given by Kolliker or Dumeril I can corroborate 

 completely. 



The differences in structure which exist between Axolotl and Am- 

 blystoma are considerably greater and more important than those 

 between neighboring genera, yes, greater than are found between 

 the. families of the Urodela. The genus Siredm without any doubt 

 belongs to a different suborder from the genus Amblystoma^ into which 

 it is occasionally transformed. Strauch, who has made the latest ar- 

 rangement of this group, separates the suborder of the Salamandrida 

 from that of the Ichthyodea by the possession of eyelids and by the 

 position of the palatal teeth in a simple row on the posterior edge of the 

 palatal bone ; while in the Ichthyodea the lids are wanting and the pal- 

 atal teeth either " stand on the front edge of the palatal bone or cover 

 the whole surface of the palate as brush-like clusters." How would it 

 be possible now to regard anatomical characters standings© far asunder 

 as transformations which had been suddenly called forth by a single 

 operation of varying conditions of life ? 



Hand in hand with the falling out of the old palatal teeth and the ap- 

 pearance of new goes a change in the anatomical structure of the verte- 

 bral column, and, as we may conclude from Kollikee's entirely ac- 

 curate observation on the stoppage of the slimy secretion from the skin, 

 in the histological structure of the skin itself. 



Who would undertake to explain all these deep-lying changes as the 

 direct and sudden effect of any external influences whatev^er o])erating 

 but oncef And even if any one had an inclination to explain them as 

 results of the loss of the gills, and therefore as correlative changes, what 

 would such a correlation be but the newly christened vital energy above 

 spoken of? For if from one variation caused by direct influence of 

 external agencies the whole body can through correlation transform itself 

 in a couple of days just so in all its parts as it appears best adapted for 

 the new conditions of life in which it is henceforth to be, then the word 

 correlation is only a term, by which nothing is explained, but the 

 search for a better explanation is hindered. Then it is preferable that 

 we simply acknowledge our belief in a phyletic vital energy. 



Moreover it certainly is not allowable even to wish to seek an explana- 

 tion of that sort (by correlation), for ice know some Urodela in the adult 

 state have no gills, and yet possess all other marks of the Ichthyodea : lack 



