No. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 561 



blood stream. In these forms there appears to be some 

 inhibition of the secretory (excretory) functions of the 

 thyroid, and the hormone is retained within the gland 

 vesicles. 



The experimental animals and their controls were kept 

 in large aquaria with plenty of water and food. One 

 of the grafted animals had metamorphosed by June 

 27. Three others transformed by July 1 ; a fifth animal 

 died without transforming July 6. The two remaining 

 axolotls had not metamorphosed by September 1. Dur- 

 ing the interval between May 21 and September 1, all of 

 the controls spontaneously transformed. The experi- 

 ment is, of course, without significance because of the 

 unstable nature of the control material. It is highly 

 probable that the operated animals would have meta- 

 morphosed just about as rapidly if the thyroid had been 

 left in its normal position. 



ExpEKiMENT 2. Homoplastic Thyroid Transplantation 

 Five seven-inch axolotls were engrafted intraperitone- 

 ally with the thyroid gland of other animals of similar 

 size and appropriately controlled by animals transplanted 

 with pieces of muscle tissue. 



The transplants were made May 2, 1922. One animal 

 had transformed by June 3, a second by June 6, a third 

 June 11. Two animals remained as larva and were re- 

 engrafted June 11 with axolotl thyroids, and metamor- 

 phosed by July 3. In the meantime the controls also 

 transformed. A large series of transplantation experi- 

 ments were performed, using various endocrine glands,' 

 but in every case except two experiments the controls 

 metamorphosed along with the operated individuals. 



Heteroplastic Thyroid Transplantation 

 Four eight-inch axolotls were engrafted intraperitone- 

 ally with the glandular tissue of adult Necturus maciila- 

 tus. Each axolotl received the entire thyroid of a single 



