88 PIGMENTARY GROWTH AFTER ABLATION OP 



none of the animals included in these three classes are atrophic, 

 though the epithelial hypophysis be but one-sixth of its normal 

 size; indeed, those included in the second class exhibit greatly 

 hypertrophied thyroids with the frequent formation of accessory 

 glands (table 7, p 7, p 9, p 10). It will further be recalled 

 that only the specimens of the second and third classes com- 

 pleted metamorphosis, while those of the first class underwent 

 an abrupt and persistent metamorphic stasis at some stage in 

 this process. It would thus appear that by the slight reaction 

 between the true neural and the buccal components of the hy- 

 pophysis, a sufficient ' hormonal ' substance was supplied to cause 

 an hypertrophic response of the thyroid gland. 45 These tad- 

 poles metamorphosed (class 2, specimens p 7, p 9, p 10). On 

 the other hand, if a larger amount of secretion was supplied 

 by the pituitary (class 3, specimen p 8), no hypertrophy of the 

 thyroid then resulted. A tentative explanation of the correla- 

 tions obtaining between the epithelial and neural lobes of the 

 hypophysis and the thyroid in the first class of animals, those 

 in which no contact is made between the true neural lobe and the 

 epithelial fragment, is more difficult. Since the thyroid is of 

 normal size in these animals, it is evident that no compensatory 

 response of this gland was evoked, although there would seem 

 to be a need for such a response, since these animals did not 

 complete metamorphosis. It would appear that some inter- 

 action .between the true neural lobe and the epithelial lobe is 

 necessary in order to evoke a hypertrophic response of the thy- 

 roid. Thus a functional specificity attends this union of true 

 neural lobe tissue with the reduced epithelial component of the 

 gland. The thyroid does not hypertrophy and metamorphosis 

 appears never to be completed when the epithelial hypophysis 

 comes in contact with only an atypical or a new neural lobe. 



46 It is of interest to note in this connection that the thyroids, which were sub- 

 jected to microscopic examination, in Cushing's canine hypophysectomies, ex- 

 hibited an excess of colloid. Further, that partial hypophysial extirpations in two 

 human patients resulted in thyroid enlargement (Exner, cit. after Gushing). 



