126 



BENNET M. ALLEN. 



this color change will be discussed later. The operation and the 

 absence of the hypophysis have their influence upon the size of 

 the tadpoles. 



Lots 2 7 (a) and (b) also 27 X (control operated) (a) and (b) 

 were measured on May 16 giving the following results: 



It is to be remembered that 27 X a and b was performed I day 

 later than 27 a and b. 



It is thus seen that although the operated controls did not grow 

 as rapidly as the unoperated controls they grew decidedly more 

 rapidly than did the operated tadpoles. It is also seen that a 

 few of the largest operated tadpoles showed greater size than the 

 smaller controls. It is difficult to explain this. It may be partly 

 due to a difference in vitality. 



The serious mortality and delay of growth are in sharp contrast 

 with the results of the equally severe operation of removal of the 

 thyroid anlage. This was performed by making a transverse cut 

 between the heart and the thyroid, and then picking out the 

 latter by means of a needle. The cut was quite as large as that 

 made for the removal of the hypophysis and produced a con- 

 siderable loss of blood, yet there was no greater mortality in the 

 operated tadpoles than among the controls. In time they ap- 

 peared precisely like the normal controls and remained so until 

 the legs began to grow in the controls while remaining at an 

 early stage of development in the thyroidless tadpoles. 



Returning to the experiments upon removal of the hypophysis, 

 upon the question of mortality my results are quite at variance 

 with those of Dr. Smith who found that there was even less 

 mortality among his operated tadpoles than among his controls. 

 I feel that this difference between his results and mine may well 

 be explained by the fact that our material was reared in a different 

 water supply. It is quite significant that lots 156 and 17 raised 



