504 



BENNET M. ALLEN 



In my experiments upon removal of the anterior lobe anlage 

 of the hypophysis of the tadpole (Allen, Biol. Bull., March, 

 '17) it was shown that the operation had an extremely unfav- 

 orable influence upon the tadpoles. I have advanced the sugges- 

 tion that the hypophysis plays an important role in metabolism 

 even during these early stages, and that in its absence the tadpole 

 is unable to cope with the heavy mineral content of the water. 



Nothing of this kind was seen in the early development of the 

 tadpoles deprived of the thyroid gland but still retaining the 

 hypophysis. They in no wise differed from the controls in 



Text fig. 3 Outlines of heads of a large thyroidless tadpole and of a normal 

 tadpole of a corresponding stage of differentiation. 



form, color, vitality or in any other observable character. There 

 is no evidence of any modification in the operated tadpoles until 

 the hind legs begin to grow. These reach a length of 4 to 5.5 

 mm. and then cease to develop when the tadpoles cease to grow. 

 The fore limbs never break through the skin but are to be found 

 in a most undeveloped condition only after careful dissection. 

 It is thus clear that both the hind and fore limbs can start to de- 

 velop in the total absence of the thyroid gland but their devel- 

 opment ceases at an early stage. In the case of the hind legs, 

 this is quite readily seen. The tail also retains its larval pro- 

 portions. It is impossible to give any tail measurements of value 

 in this series because as explained, the tails of both thyroidless 



