On Amphibian Metamorphosis and Internal Secretions. 45 



toxic consequences. All our endeavours confirm the conclusion of Jensen 

 that iodine free of organic combination is not efficacious in producing meta- 

 morphic changes in the Axolotl. It is thus evident that in the neoteny of the 

 Mexican Salamander it is not primarily the exogenous factors (available 

 iodine supply and temperature) contributing to normal Amphibian meta- 

 morphosis that are significant. 



Hence it became desirable to test the effect of administering other ductless 

 glands. In this connection the results of D. I. Macht (1919), who has claimed 

 to accelerate transformation in frogs by prostate-feeding, as also Bennet 

 Allen's experiments (1920) on the part played by the pituitary gland (anterior 

 lobe), demanded some attention. On the other hand the experience of 

 Gudernatsch (1914) and others does not indicate the likelihood of influencing 

 Amphibian metamorphosis by administration of pituitary gland per os. 



Both young (4 to 6 months) and old (18 months) larvae were fed with pituitary 

 gland (anterior lobe). In the experiments glands of both old animals (ox) and 

 of calves were employed and the treatment was continued for three months 

 without producing metamorphic phenomena. As an illustration, particulars 

 of the following experiment will serve. Fresh ox pituitaries were obtained 

 from a slaughter-house, and the posterior and anterior lobes separated. On 

 October 2, 1920, four vessels were prepared with four larvae in each, which 

 were nearly 6 months old. Those in vessel A were fed on thyroid ; those 

 in B on pituitary anterior lobe (henceforth called pituitary for brevity's sake, 

 since posterior lobe was never employed in any of these experiments) ; in C on 

 thyroid and pituitary on alternate days ; and in D on raw meat, as controls. 



Those fed on thyroid showed the first visible signs of transformation on the 

 14th day, their gill-filaments were resorbed by the 21st day, and the meta- 

 morphosis was morphologically complete on the 26th day. The controls 

 showed no change throughout. Those fed on pituitary have showed no 

 metamorphic changes at all ; three were kept on the diet for 3 months, one for 

 8 months. It is obvious that the diet has no effect on their transformation. 

 Those fed alternatively upon pituitary and thyroid metamorphosed in a 

 perfectly normal way ; the process, however, took slightly longer, the first 

 signs of change appearing two days later than in those fed only on thyroid, 

 the total resorption of the gill-filaments, and the morphological completion of 

 the process, each taking place 3 days later than with the thyroid-fed ones. 



The rates of growth upon the different diets are illuminating ; they may 

 best be presented in tabular form : — 



