FEEDING EXPERIMENTS ON TADPOLES 437 



ment was discontinued, none in either group had hind legs out, 

 although spleen-fed ones showed leg buds. 



The three groups of tadpoles fed on adrenal cortex (fig. 1 /, 1 r), 

 adrenal medulla (fig. 1 g, It) and ovary (fig. 1 e, 1 p) were dur- 

 ing the first weeks of growth behind the muscle, liver, spleen and 

 thymus groups. Later, however, they grew more rapidly. Some 

 of those fed on ovary actually reached the average size of the 

 faster groups and completed their metamorphosis at the approx- 

 imate age of 105 days. 



The adrenal cortex tadpoles were somewhat faster in develop- 

 ment and grew better than the adrenal medulla ones. The former 

 budded hind legs on the 71st and the latter on the 81st day. At 

 the conclusion of the experiment the adrenal cortex ones had 

 strong well developed legs, while the legs of the medulla-fed 

 individuals were still short and drawn close to the body. 



In previous experiments, in which adrenal cortex and medulla 

 had not been given separately, it was seen that the adrenal-fed 

 tadpoles became extremely light in color after 3 or 4 weeks of 

 feeding. The pigment cells were found to be completely con- 

 tracted. The suggestion was made ''that the extract from the 

 chromaffine cells of the medulla which dissolved in the water 

 caused the pigment cells to contract" and "former experiments 

 with adrenalin would warrant such a suggestion." In the present 

 experiments, however, separate sets of tadpoles were fed on cor- 

 tex and medulla respectively. After 5 weeks' feeding those fed 

 on adrenal cortex became much hghter than those fed on adre- 

 nal medulla or any other food. This difference in color became 

 more evident as the experiment proceeded, until the cortex-fed 

 tadpoles had an extremely light, greenish-yellow tint. Thus the 

 above suggestion is doubtless incorrect, at least in these experi- 

 ments, yet the true cause of the light pigmentation is still obscure. 



These cortex-fed tadpoles also differed from the other groups 

 in still another feature, namely, the peculiar triangular shape 

 (fig. 7 6) of their bodies described above. A few of the brain-fed 

 tadpoles somewhat approached this condition. 



The chief purpose of feeding the set I on different foods was 

 to study the influence of the thyroid treatment, after the ani- 



