532 W. W. SWINGLE 



eight days of the experiment. None of the controls revealed 

 an3 r indications of limb development, nor any other of the 

 structural changes exhibited by the thyroid fed larvae. 



November 20, marked atrophy and degenerative changes of 

 the tail became evident, the organ was so shriveled as to be 

 practically functionless. The sucker-like tadpole mouth had 

 given place to the mouth characteristic of the adult. About 

 this stage, two small prominences were observed under the 

 skin of the pectoral region. These proved upon dissection to 

 be the fore limbs. 



From November 30, on, the mortality among the thyroid- 

 fed larvae gratly increased, until by December 7th, only seven 

 larvae remained alive; six of these were killed and preserved for 

 microscopic examination of the gonads. 



The one remaining thyroid-fed tadpole was kept alive by 

 careful dieting, until December 16. During this time no fur- 

 ther metamorphic changes other than those recorded were ob- 

 served. The limb buds grew somewhat in length and differenti- 

 ated into their primary divisions The animal died a few days 

 later. 



The control animals for the thyroid-fed tadpoles just de- 

 scribed had, by December 7, increased in size considerably. 

 The average length at this time was 28 mm. Two larvae 

 measured 33 and 34 mm. respectively. All of the control animals 

 possessed tiny limb buds, though not nearly so large as those of 

 the thyroid-fed group. The fore limbs had not begun to form 

 at this time. 



Microscopic examination of the gonads revealed little differ- 

 ence in size or development between the glands and germ cells 

 of the thyroid-fed and control larvae. 



It was impossible to obtain a record of the normal rate of 

 growth and development of the gonads in the short space of 

 time the experiments continued, whicli was twenty days for the 

 oldest larvae. It matters little, however, whether the normal 

 rate is slow or rapid, thyroid feeding did not accelerate growth 

 or development of the gtrm glands and cells of the experimental 

 animals over that of the controls. As was the case with the 



