366 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 



The five Amblystomas, on wbicli I have reported bere, have shown, up 

 to the present time, no appearances of reproduction. 



It is evidently an objection that will very poorly stand the test when 

 Sacc * attributes the sterility of tbe Amblystomas reared from Axolotls 

 to "poor food." Wby, then, do tbe Axolotls reproduce so easily wben 

 tbey are fed exactly tbe same ? I can also state expressly that my Am- 

 blystomas are quite excellently' fed. To be sure, these have hardly reached 

 tbe age of one and a half years; but the Axolotls propagate tbe second 

 year, and some of Dumeril's Amblystomas were five years old in 1870. 



The fact of sterility stands in clear opposition to the view that tbese 

 Amblystomas are the regular advanced guards of the genus Siredon as 

 it moves forward in phyletic development. To be sure I will by no 

 means maintain that my theory of reversion could actually explain tbe 

 sterility, but at least it does not stand directly in contradiction witb it. 

 Mere forms of reversion may perisb without reproducing tbemselves. 

 A neic form called forth by tbe working of an unknown phyletic vital 

 energy cannot be a sterile one, because this directly destroys again tbe 

 "purpose" wbich tbe vital energy is pursuing. Tbe idea of tbe vital 

 energy includes that of teleology. 



Moreover, from our stand-point tbe sterility of the Amblystomas may 

 be, if not completely understood, yet shown as a phenomenon that does 

 not stand quite alone. In tbe case of the Lissotriton punciatuSj as quoted 

 above, the female "larvce" were at any rate sexually mature and laid 

 «ggs, but at the same time tbe males bad no perfected spermatozoa iu 

 tbe testicles. 



Otber cases of the kind are not known to me. At tbe time wben I made 

 my experiments witb butterflies, as mentioned above, this point of view 

 was still unseen, and so I neglected to examine the artificially produced 

 forms of reversion in regard to their organs of generation. But general 

 principles also lead to tbe conclusion tbat atavistic forms may easily 

 remain sterile. 



Darwin* finds tbe most immediate causes of sterility, first, in the 

 operation of widely varying circumstances of life; and, second, in tbe 

 crossing of individuals with widely differing constitutions. Varying 

 circumstances of life are at any rate wbat induce tbe transformation of 

 the Axolotl, and from this point of view it could not be surprising if we 

 find those individuals sterile, wbich have precisely shown themselves as 

 especially affected by tbese altered conditions of life, since they have 

 reverted to the salamander form. In tbis reasoning it is by no means as- 

 serted that reversion always and icithout exception is accompanied by ster- 

 ility. Nor can it be objected to my interpretation of the Axolotl's trans- 

 formation tbat tbrough reversion a colony of Axolotls capable of reproduc- 

 tion never could have arisen. On tbe contrary, Jullien's female Triton 



"Bull. Soc. Neuchatel, Bd. viii, p. 192, a reference to tbe place in Troschel's Jabrea- 

 bericbt (Annual Rei)ort), for 18Gt). 

 * Origin of Species, 5tb edition, j). 325. 



