358 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 



letic vital energy; for the transformation is a sudden one; it leaves no 

 time for gradual adaptation in the course of generations. Indirect influ- 

 ence of the external relations of life, i. e. natural selection, is accordingly 

 excluded from the first; but direct influence of the altered circumstances 

 of life does not suffice by a great way to explain the total transforma- 

 tion of the whole structure, as I have already intimated and will now 

 show more minutely. 



The distinctions between the Paris Axolotl and its resulting Ami Cy- 

 stoma are, according to Dum^ril, Kolliker, and my own observations, 

 the following: 



1. The gills disappear, the clefts of the gills close up, and only the 

 foremost of the arches of the gill remains in existence; the other arches 

 vanish. At the same time the Os liyoideum is changed (Dumeril). 



2. The crest on the back disappears entirely (Dumeril). 



3. The rudder-like tail changes to a tail like a salamander's (DuMiiiRiL)^ 

 which nevertheless is not quite circular in section as in the salamander, 

 but is somewhat compressed laterally (Weismann). 



4. The skin gets yellowish- white patches, irregularly distributed on 

 the sides and the back (Dum:i&ril), while at the same time its former 

 ground color of grayish-black changes to a shining greenish-black (Weis- 

 mann), and, besides, the shiny secretion from the skin is lost and the 

 glands of the skin become indistinct (Kolliker). 



5. The eyes become prominent and the pupils small (Kolliker), and 

 eyelids are formed which can close the eye completely, while in the 

 Axolotl only a narrow circular fold surrounds the eye, and it cannot be 

 closed (VVeismann). 



6. The toes diminish in size and lose their skin-like appendages (Kol- 

 liker), or, more precisely, the half web-membranes which unite the 

 inner ends of the toes on all the feet (Weismann). 



7. The palatal teeth in this, as in all Amblystomas, stand in a diag 

 onal row, while in the Axolotl, like the Triton laivse, they stand at the 

 side of the palatal vault forming an arched band, with several rows of 

 teeth.* (Dumeril. See his figure. Zeitschrift f. wissensch. Zool., xxv 

 Bd., Sup., p. 279.) 



8. In the Axolotl the under jaw has, besides the teeth on the upper edge 

 of the bone, some very small teeth disposed in several rows; these latter 

 disappear after the metamorphosis (Dumeril). I add that the permanent 

 teeth belong to the os dentaJe, the temporary ones to the os operculare.f 



* Dumeril has the teeth of the vomer separated ftoin those of the os palatinum by a 

 gap. Probably this was an artificial one, as Gagenbaur (Friedricii & Gagenbaur, 

 "Der Scbiidel des Axolotl"— The Skull of the Axolotl— Wlirzburg, 1849) figures the 

 rows of teeth without interruption, passing over from one bone to the other. The 

 Bame was true in three Axolotla which I examined in regard to this iioiut; moreover, 

 this little dilfereuce is quite unimportant in the question here treated. 



t See O. Hertwig, " Ueber das Zahnsystem der Amphibien und seine Bedeutung fiir 

 die Genesis des Skelets der Mundhoble." (On the Dental System of the Amphibia, and 

 its Significance for the Geuesis of the Skeleton of the Mouth.) Arch. f. Mikroskop. 

 Anat., Bd. xi, Supjjlemen theft, 1874. 



