EFFECT OF EXTIRPATION OF THYROID 601 



The average of the thymus glands for the young frog controls 

 was 182, table 2. This volume varied in the different specimens 

 from 110 to 286. The thymus glands of each of the three oldest 

 thyroidless tadpoles is represented by* 575, 1219, 940, and 475 

 respectively (tables 2, 8, 9, and 10). It is clear that in none 

 of the young sexually mature frogs were the thymus glands 

 as large as in the four oldest thyroidless tadpoles. The thymus 

 gland of the young sexually mature control frogs is much smaller 

 than that of the recently metamorphosed control frogs and the 

 control tadpole has larger thymus glands than the recently 

 metamorphosed frogs. The thymus degenerates as maturity is 

 reached in most forms and this is what is happening here. In 

 the case of the thyroidless tadpoles this degeneration has 

 not taken place and instead the thymus gland has developed 

 more and has grown during a longer period of time. 



It is interesting to note here that the thyroidless tadpole killed 

 February 7, table 2, no. 8, has well developed thymus glands in 

 spite of the fact that the tadpole is sexually mature with 

 many live sperm. -The thymus gland has persisted after sexual 

 maturity was reached. 



THE GRAPHICAL REPRESENTATION OF THE VOLUMES 



The number of thyroidless tadpoles used as a basis for the 

 graphs described below was so small that the curves should be 

 accepted as showing general features and not as showing the 

 accurate details of growth. The volumes of the pituitary glands 

 in both the thyroidless and the normal tadpoles do not vary 

 much until the period of metamorphosis (table 1). The line for 

 the thyroidless tadpoles remains high until the February 22 

 specimen is reached when it comes down only to go up again 

 for the March 3 thyroidless tadpole (chart 1). The line for the 

 control specimens comes up gradually until the young sexually 

 mature frog stage is reached. The great deviation in the volume 

 of the pituitary gland of the thyroidless tadpole killed February 

 22, table 2, no. 9, is probably due to individual variation and has 

 no great significance. 



