602 JAMES B. KOGERS 



The line of growth of the thymus glands in the thyroidless 

 specimens mounts rapidly after the September 25 specimen 

 is reached. It reaches its greatest height in the February 7 

 specimen and then drops. The sudden decline might mean 

 degeneration but on account of the few thyroidless tadpoles 

 observed it could not be determined. 



The line for the normal control mounts very high during the 

 period of metamorphosis. It then comes down sharply to the 

 recently metamorphosed frog stage and slopes off gradually to 

 the young sexually mature frog stage. 



SUMMARY- 



1. The pituitary gland continues to develop when the thyroid 

 gland is extirpated and the anterior lobe reaches a larger size 

 actually and relatively than in normal specimens. In most 

 cases it is larger than the pituitary gland of the corresponding 

 control even without reference to body length. It is at its 

 largest in proportion to body length in thyroidless tadpoles that 

 are of the same age as young sexually mature frogs. 



2. The thymus gland develops when the thyroid gland is 

 extirpated. The thymus glands of normal controls are larger 

 during the period of metamorphosis and immediately following 

 than at any other period of the frog's life. 



3. The young sexually mature frogs have smaller thymus 

 glands than do thyroidless tadpoles of the same age. 



4. The thymus glands of thyroidless tadpoles do not migrate 

 to the position in which the thymus gland is found in adult 

 frogs. 



5. The thymus gland of the thyroidless tadpole does not 

 degenerate like that of a frog that develops normally. 



