500 



BENNET M. ALLEN 



development of the gonads and germ cells. Two of my graduate 

 students are working upon the effects of this operation upon 

 other organs. Mr. George Terry is studying the effects upon 

 the skeleton and Mr. James Rogers is investigating the effects of 

 its removal upon the other glands of internal secretion. 



Text fig. 1 Diagram of a sagittal section of the tadpole at the stage when the 

 operation is carried out. This shows the position of the thyroid anlage. The 

 dotted line immediately behind it shows the plane in which the cut is made. 



The thyroid anlage was removed at its very inception in tad- 

 poles of 6 to 7 mm. total length. This was done by making a 

 transverse cut between the thyroid anlage and the pericardial 

 cavity as shown in text figure 1. With some practice it was 

 possible to do this quite accurately. The cut was quite deep 

 usually laying open the ventral portion of the pharynx cavity. 

 The thyroid anlage is pigmented and with some practice it can 

 be recognized with great precision. As results will show, there 



