596 JAMES B. ROGERS 



2). For the most part the pair of thymus glands approximate 

 each other in size. Thyroidless tadpole 7 shows a marked dif- 

 ference in the size of the two thymus glands. This variation 

 is thus found in both thyroidless and control specimens. 



COMPARISONS OF THE ANTERIOR LOBE OF THE PITUITARY GLAND 

 AND OF THE THYMUS GLANDS IN YOUNG TADPOLES 



In comparison there is nothing striking in the 10.5, 13, and 

 24 mm. total length (table 1), respectively except in the growth 

 of the normal thymus. Both the pituitary gland and the 

 thymus are slightly larger in the 10.5 mm. control tadpole. 

 The 13 mm. thyroidless tadpole has somewhat larger glands 

 than the 14 mm. control tadpole. The 24 mm. control tadpole 

 has better developed glands than the 24 mm. thyroidless tad- 

 pole. Here it is noticed that the normal thymus has made a 

 markedly greater increase than that of the thyroidless tadpole. 

 This proves nothing at this stage but it gives a hint as to the 

 further growth of the thymus gland in the larval frog. 



COMPARISONS OF THE ANTERIOR LOBE OF THE PITUITARY GLAND 

 AND OF THE THYMUS GLANDS IN METAMORPHOSING NOR- 

 MAL TADPOLES AND THYROIDLESS TADPOLES OF COMPAR- 

 ABLE AGE 



The period of normal metamorphosis for Rana pipiens ex- 

 tends from June to August, depending on the time at which 

 the eggs were laid, the season, the food, etc. The thyroidless 

 tadpole 4 {table 2) was killed September 25, 1916 and had a 

 body length of 36 mm. This specimen was killed soon after 

 the time when normal metamorphosis took place. The largest 

 of the metamorphosed control tadpoles, No. 10 (table 2) had a 

 body length of 34 mm. The average body length of these 

 controls was 30.16 mm. The thyroidless tadpole (table 2, no. 

 4) killed September 25, had a pituitary gland which with body 

 length correction was represented by 483. The average of the 

 pituitary glands of the normal metamorphosing tadpoles on 

 the same basis was 152. The pituitary gland of the thyroid- 

 less tadpole was thus very much larger than the average for the 



