Ko. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 563 



injection of fresh pituitary substance does induce axo- 

 lotl metamorphosis possibly by serving to release the 

 thyroid hormone. This experiment should be tried on 

 the Mexican strain of axolotl which apparently rarely 

 spontaneously metamorphoses and hence can be safely 

 controlled. 



THYROmECTOMY AND MeTAMOEPKOSIS 



Eight axolotls varying from seven to fourteen inches 

 were thyroidectomized and at the present writing, Sep- 

 tember 1, are still larva^ and show no indications of 

 transforming. Out of the original one hundred and nine 

 animals received from New Mexico these eight are tlic 

 only ones that have not metamorphosed. It is a fairly 

 safe assumption that these axolotls will remain perma- 

 nently as larva now that the thyroid gland is lacking.' 



The thyroids of several animals were removed after 

 the onset of metamorphosis, i.e., after the tail fin and gills 

 were undergoing reduction, but in all cases the removal 

 of the thyroid failed to prevent the completion of meta- 

 morphosis. 



Discrssiox 



The conclusion to be drawn li-oin tlicsr cxnt rnih iits is 

 that the New Mexican strain ol axoloil ciii i too 

 unstable to work with on an\' problem iii\-olving the 

 methods of feeding, injection or transplantation, where 

 the results require a lapse of several weeks to obtain. 

 The animals can not be controlled when the thyroid ap- 

 paratus is left intact. It is evident that conclusive ex- 

 periments of the above kinds on the New Mexican strain 

 of axolotl (where the animals themselves are used as 



