METAMORPHOSIS OF NEOTENOUS AMPHIBIANS 405 



The thyroid glands were compact and large — larger than the 

 glands of newly metamorphosed R. clamata frogs — and made up 

 of large and small follicles filled with colloid. The blood supply 

 to the glands was rich, apparently much more so than is the case 

 with larval anurans; only a superficial examination was made to 

 test this point because of the lack of sufficient material. 



The pituitary gland was also examined; the pars anterior 

 seemed normal or possibly rather small when the relative sizes 

 of all the lobes are considered. 



The thyroids were dissected out and each gland cut into three 

 pieces of approximately equal size. Each piece of tissue was then 

 transplanted intraperitoneally into immature Rana clamata 

 larvae averaging 51.5 mm. total length with hind-leg buds 2.2 

 mm. undifferentiated. A few hours following grafting one 

 tadpole jumped out of the container and was found dead, leaving 

 but five transplanted tadpoles. Eight days after transplanting 

 the pieces of axolotl thyroid, the engrafted tadpoles showed all 

 the characteristic features of hyperthyroidism, such as cessation 

 of growth, marked acceleration of limb development, tail atrophy 

 and resorption, and body emaciation. 



August 20th, or twelve days after transplantation, four of the 

 engrafted animals were found dead (figs. 8 to 10). The photo- 

 graphs show very well the marked tail atrophy and resorption 

 and the fore-leg development. The early death of the animals 

 was due to the great acceleration of metabolism and metamorphic 

 change. Undoubtedly, smaller pieces of the axolotl thyroid 

 would have had the same effect upon metamorphosis without the 

 too destructive rise in katabolic activity. The amount of t^il 

 resorption can be judged by the fact that during the twelve days 

 of the experiment the average total length of the tadpoles 

 decreased from 51.5 mm. to 29.6 mm. The control animals 

 remained unchanged.^ 



^ Since this was written one hundred and nine large axolotls were obtained by 

 Professor Harrison from Albuquerque, New Mexico, and given to me for experi- 

 mentation. This experiment was repeated on a large scale with identical results. 

 Mr. Carl Mason, of this laboratory, metamorphosed thirteen normal, thyroidless, 

 and pituitaryless R. sylvatica tadpoles by transplanting pieces of the thyroid of 

 a single 14-inch axolotl. 



