Kansas Acadenii/ of Science. 245 



EXPERIMENTS UPON THE EXTIRPATION OF THE 



PITUITARY AND THYROID GLANDS 



IN TADPOLES. 



Bennet M. Ai.lkn'. 



IN recent years great interest has been aroused in the glands 

 of internal secretion. It has been found that these play a 

 role of fundamental importance in metabolism and develop- 

 ment. It is the latter phase of the subject that has especially 

 appealed to the author and the students whom he has started 

 in this line of investigation. While there has been a large 

 amount of work done upon these glands in adults, there has 

 been comparatively little study of them in embryos. The 

 reason is not far to seek, since our interest is chiefly stimulated 

 by the importance of these glands to medicine. The investiga- 

 ors have naturally turned to the mammals for experimental 

 study. In the study of embryology the development of the 

 chick has chiefly attracted attention. 



Now neither the mammals nor the birds nor reptiles afford 

 ready facilities for the study of the functions of these glands 

 during embryonic development. A few years ago Gudernatsch 

 carried on some stimulating and suggestive work upon the 

 effects of feeding thyroid preparations to tadpoles. He was 

 able by this means to greatly accelerate metamorphosis, caus- 

 ing a precocious development into the adult condition. It 

 occurred to the author that since such precocious development 

 was produced by an excess of thyroid material, an inhibition 

 of metamorphosis might be produced by the removal of the 

 thyroid gland. This is an extremely simple process, being 

 accomplished by making a transverse cut just back of the 

 thyroid gland, at the beginning of its development, in Rcma 

 pipiens tadpoles of 6.5 mm. total length. The tadpoles thus 

 deprived of the thyroid gland developed in a perfectly normal 

 fashion up to the time when the hind limbs began to grow. 

 These limbs reached a length of four to five mm. and then abso- 

 lutely ceased developing. This cessation of differentiation was 

 not only seen in the case of the limbs, but was evident in the 

 length of the intestine, characteristics of the mouth, the per- 

 sistence of the tail, and the development of the skeletal system. 



