THYROID REMOVAL IN LARVAE OF RANA PIPIENS 501 



was occasional failure to remove the thyroid anlage. These 

 cases were probably due to failure to remove all of the gland 

 when it was cut in two as frequently occurred. Whenever this 

 was noticed both portions were removed. Care was usually 

 taken to remove the portions of the pharynx floor adjacent to 

 the point from which the thyroid anlage was growing. In some 

 instances there might have been a renewed growth of the anlage 

 from the point of origin. 



It may be well to point out that one can always determine the 

 presence or absence of the thyroid gland in later stages preserved 

 for study. This was done by a painstaking study of sections of 

 the lower jaw back to and including the anterior portion of the 

 heart in all specimens used to establish cardinal points in this 

 work. The epithelial bodies (parathyroid glands) were not re- 

 moved, nor was there any evidence that the results detailed be- 

 low were secondarily caused as a result of failure of other glands 

 of internal secretion to develop to full functional capacity. 



The thyroid anlage was removed with a cataract needle. 

 Within half an hour the wound had completely healed and the 

 tadpoles appeared to be quite normal. 



It may be pointed out that the mortality which decimated the 

 half grown tadpoles was due to failure to care for the specimens 

 properly, since the controls showed just as high a mortality as 

 did the thyroidless tadpoles. In spite of the loss of specimens 

 due to failure to provide ideal conditions for them, a sufficient 

 number were retained for firmly establishing the points set forth. 

 At this date, June 10, 1917 three thyroidless tadpoles are still 

 alive — considerably over a year after the operation, and twelve 

 have been killed at various dates from September 20 to the 

 present time. Others were preserved at frequent intervals be- 

 tween the time- of operation and that date, so it will be seen 

 that there is an ample amount of material at hand. 



