406 W. W. SWINGLE 



The pituitary gland of the axolotl was also engrafted into an 

 immature larva of R. clamata, measuring 45 mm. total length, 

 hind limbs 2.5 mm. long and differentiated into thigh and shank, 

 but without toe points. All three lobes of the gland were trans- 

 planted together. The success of the graft was attested by the 

 color change in the larva induced by the expansive action of the 

 pars intermedia secretion upon the melanophore system. 



Eighteen days after the graft was made the animal had not 

 changed in any way either in regard to limb development or 

 growth, so the experiment was abandoned. Examination of the 

 implanted gland showed it to be mostly resorbed. 



The negative result following grafting of the axolotl pituitary 

 is in striking contrast to that obtained when the pituitary of a 

 newly metamorphosed frog is transplanted into immature anuran 

 larvae. However, it must be remembered that in the latter case 

 we are dealing with a homoplastic graft and in the former with 

 a heteroplastic one, and a single transplant at that. It is un- 

 fortunate that a larger amount of axolotl material was not 

 available, for it is of importance to know whether or not the 

 pituitary gland of the axolotl is active, and some idea of its 

 potency can be obtained by testing its effect upon limb develop- 

 ment of anurans. If the results are consistently negative, then 

 it is probable that the gland is defective in so far as its relation 

 to the thyroid mechanism is concerned. 



The results obtained by grafting portions of axolotl thyroids, 

 are clear-cut and admit of but one interpretation: namely, that 

 the thyroid apparatus of this animal is highly active and potent 

 in inducing marked metamorphic change when transplanted into 

 immature anurans, but is apparently incapable of initiating 

 metamorphosis when left unmolested in its normal place. This 

 experiment seems to rule out the idea that the axolotl's thyroid 

 secretion is defective. If the thyroid glands of a single axolotl 

 when cut into six fragments are capable of initiating metamorpho- 

 sis in five anuran larvae grafted with a single fragment (the sixth 

 animal died) within ten to fourteen days, surely we may safely 

 assume that the same glands, entire, contain enough of the active 

 hormone to initiate metamorphosis in the single axolotl of which 



