GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 17 



in normal metamorphosis. A part of the shrinkage noted in 

 this experiment was due to loss of water from the tissues, as 

 happens to some extent during normal metamorphosis. 



Discussion. From the results given in the numerous papers 

 dealing with thyroidectomy in higher animals it was to be ex- 

 pected that definite and striking results would be obtained by 

 thyroidectomy in amphibia. Rogowitsch ('89) found that this 

 operation in mammals causes hypertrophy of the hypophysis 

 and Stieda ('90) noted an increase in the number of 'chief cells 

 of this gland. Herring ('08) stated that thyroid extirpation in 

 mammals causes increased activity of the pars intermedia of 

 the hypophysis, bringing about colloid formation. He reported 

 also a proliferation of the cells in the posterior lobe. Hofmeister 

 ('94) stated that this operation in mammals produces cachexia, 

 resulting in abnormal growth, especially of the bones. Ceni 

 ('05) stated that thyroidectomy in fowls causes interference with 

 egg production. Gudernatsch ('12, '14, '17) and several others 

 have shown that feeding thyroid to larval frogs hastens the 

 time of metamorphosis and checks general growth, hence results 

 somewhat opposite to those were to be expected in our experi- 

 ments. The effects produced by feeding thyroid to young am- 

 phibia are probably not due to any specific metamorphosing 

 function of the thyroid, but rather to a perversion of metabolism, 

 since they have been produced with thyroid substance of mam- 

 mals which do not undergo metamorphosis as do the amphibia 

 used in the experiments. Feeding thyroid to mammals increases 

 metabolism and causes hypertrophy of various organs, including 

 some of the ductless glands (Hoskins, '16). It was also to be 

 expected that the operation we performed might affect the hypoph- 

 ysis, since Smith ('16, '17) noted that after hypophysectomy 

 in young frogs embryos the thyroid failed to develop normally, 

 and Allen ('17) obtained somewhat similar results. 



The earliest apparent and most extensive differences between 

 the thyroidless and control frog larvae are in the skeletal ele- 

 ments. As Terry ('18) has well described, calcification and ossi- 

 fication (especially the latter) progress less rapidly in the thy- 

 roidless larvae than in the controls, and finally these processes 



