510 BENNET M. ALLEN 



The thyroid region of this thyroidless tadpole killed February 

 7 was sectioned and it was clearly demonstrated that the thyroid 

 gland was absent. It is interesting to compare the gonads of 

 this specimen with those of two young male frogs killed February 

 26. These young frogs had transformed the summer before and 

 had lived in the open until captured by the dealers from whom 

 they were purchased. They were secured from a Chicago firm. 

 Although their exact history is not known, it is clear that they 

 are quite as old as the thyroidless tadpoles with which compari- 

 son is made. We find that in one of the young frogs of 51 mm. 

 body length, the testes are slightly smaller in transverse section 

 than in the thyroidless tadpole killed over two weeks earlier in 

 the season. In the other frog of 56 mm. body length, the gonads 

 are somewhat larger in transverse section than in the thyroidless 

 tadpole mentioned above, but are roughly proportional to the 

 difference in body length. 



A comparison was made between the volumes of the testes of 

 the older controls and the volume of the testes of the February 

 7 thyroidless tadpole. It was manifestly impossible to estimate 

 the exact volume, so a rough estimate was made by multiplying 

 together the average width, thickness and length as given in the 

 table, giving a certain numerical basis for comparing the size 

 of these structures. Correction was made for differences in body 

 size by taking an average of the body length of the two classes 

 to be compared, and then multiplying the value found to repre- 

 sent the testis average of the thyroidless tadpoles by a fraction 

 in which the average body length of the controls is the numer- 

 ator and the average body length of the thyroidless tadpoles the 

 denominator. This does not give a completely accurate basis 

 of comparison, because these body lengths are not comparable, 

 i.e., the body of the tadpole normally shrinks during metamor- 

 phosis. The results were as follows: 



mm. 



Average of MC 4) MC 5 , and MC 6 1 .4611 



Average of the two testes of MT 5 1 . 140S 



Undoubtedly, the thyroidless tadpoles were under a serious 

 handicap as regards nutrition. The malformation of the tails 



