3G0 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSIOMA. 



of the eyelids, characteristic type of the palatal teeth, aad of the arrange- 

 ment of the lingual bones. Such are the genera Amphiuma L., Meno- 

 2)onia Harl., and Gryptohranchus v. d. Hoev. The first two genera, as is 

 well known, still have the clefts of the gills. Gryptohranchus, on the 

 contrary, has lost these clefts, which are grown over with skin as in the 

 A))ihIystoma, and yet, by the unanimous testimony of all systematic 

 zoologists, it is a genuine fish-lizard in habit, arrangement of the lingual 

 bone, i)alatal teeth,* &c. It must be added that even the Axoloil itself 

 may lose the gills tcithout, on that account, changing to an Anihlystoma. I 

 have meulioued elsewhere that in Axolotls which are kept in water that 

 is shallow and still, the gills frequently grow small; but it also happens 

 that they shrivel up entirely. I have an Axolotl preserved in spirits, 

 in which the gills are shriveled to little irregular bunches; at the same 

 time the crest on the back is so completely wautiug that a longitudinal 

 furrow has appeared in its place, and on the tail the border of skin has 

 entirely vanished from the lower margin, and about half from the upper. 

 Nevertheless, the animal is widely separated in structure from the 

 Amblystoma : it has the arches of the gills, the palatal teeth, the skin, 

 &c., of the Axolotl. 



This demonstrates, therefore, that the loss of the gills hy no means must 

 ahcays bring after it all the other variations which tve see take j)lace in the 

 metaynorjihosis of the Axolotl ; that these, therefore, are by no means the 

 necessarily and immediately appearing result of that loss. Whether they 

 must necessarily appear after long successions of generations, whether 

 also the descendants of Gryptohranchus will some time in the future take 

 the structure of the Salamandrida, that is another question which I 

 should not like to answer just in the negative, but which does not come 

 into the account here, as we are considering only a possible sudden result 

 from the loss of the gills. 



The question, therefore, seems to stand thus : Either onr apprehension 

 up to this time of the transformation history of the Axolotl as a further 

 development of the species is incorrect, or the existence of a phyletic vital 

 energy is demonstrated hy the case of the Axolotl beyond the possibility of a 

 refutation. 



Now the question comes up, whether the facts of this transformation 

 history do not also admit of another explanation. I believe that tbis is 

 at any rate possible and that another interpretation may be shown as 

 the correct one with a good degree of probability. 



I esteem those Amhlystomas ichich in individual cases have developed in 

 confinement from Siredon Mcxicanus [syn. piscifoimis), as icell as from the 

 Paris Axolotl, not as forms of advancement, hut forms of retrogression. 

 I believe that the Axolotls ichich to-day live in the lahes of Mexico icere 

 already Amhlystomas a geological {or better a zoological) epoch earlier, but 



* See Straucb, Zeitsclirift. f. Wissensch. Zool., xsv Bd., Supp]., p. 10. 



