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THE AMERICAN NATURALIST [Vol. LVI 



Necturus. The experiment was performed May 15. By 

 June 11 all of the engrafted animals had transformed but 

 none of the controls for this particular group, though nor- 

 mal, untreated animals used as checks for other experi- 

 ments were metamorphosing during this interval. 



Despite the unstable nature of the control material 

 used, this experiment seems fairly sound and indicates 

 that Necturus thyroids when injected in sufficient quan- 

 tity will metamorphose axolotl. To be absolutely reliable 

 this experiment should have been performed upon thy- 

 roidectomized forms, but unfortunately the unsuitable 

 nature of the controls was not known until too late. 



Thyeoid Feeding Experiments 

 Five six-inch axolotls were fed desiccated thyroid tis- 

 sue (Parke, Davis and Company), containing 0.21 per 

 cent, iodine by weight. The feeding was done by means 

 of a pipette May 18. Two animals had transformed by 

 May 27, and all by June 10. None of the controls meta- 

 morphosed during this interval but all transformed by 

 July 25. The experiment seems trustworthy, especially 

 ill view of similar results obtained by other investigators 

 (»u animals of the European strain. 



Heteroplastic Pituitary Transplantation 

 Five axolotls varying in length from four to seven 

 inches were each grafted with two whole pituitary glands 

 of adult Rana clamafa frogs. The grafts were made May 

 . 5. June 3 one animal metamorphosed ; June 7 a second 

 transformed. June 10 the three remaining animals were 

 reengrafted with frog pituitaries. All metamorphosed 

 by June 25. 



During the interval between May 5 and June 25 only 

 two of the controls for this particular group transformed, 

 but it must be remembered that control animals of other 

 cultures were metamorphosing. The experiment is re- 

 corded for what it is worth, but the writer believes that 



