412 W. W. SWINGLE 



animals appeared emaciated and showed other symptoms charac- 

 teristic of hyperthyroidism. The controls had increased in size 

 somewhat, and microscopic examination showed tiny limb buds. 

 The iodin feeding was continued until the time of metamor- 

 phosis, which took place in a normal manner and was success- 

 fully completed by all with the exception of nine larvae which died 

 during early metamorphic change. The thyroidless animals 

 under the stimulus of the iodin completed metamorphosis in a 

 much shorter time than the normal control animals with thyroid 

 glands intact. The thyroidectomized animals used as controls 

 for the series are at the present writing very large and show no 

 signs of limb. buds. 



About this time twenty extremely large thyroidless toad 

 larvae were obtained from Miss Mary Larson, of the University 

 of Kansas. The glands of these animals had been removed 

 several weeks before; they were much larger than normal toad 

 tadpoles at metamorphosis; they were, in fact, typical giant 

 thyroidectom.ized larvae like those described by Allen. These 

 animals showed no indications of limb buds when started on the 

 iodin diet, but are at the present writing (June 12th) undergoing 

 metamorphosis. The fore and hind legs of the animals are well 

 developed; mouth is changing from larval to adult form; tails 

 almost completely resorbed. 



Four of these giant thyroidless larvae used as controls for the 

 iodin-fed culture are larger than at the beginning of the experi- 

 ment, but show no signs of limb development. 



A number of both large and small thyroidectomized tadpoles 

 were killed at different stages of the experiment and preserved 

 for microscopic examination. Careful search made for vestiges 

 of the thyroid gland have yielded only negative results. No 

 indications of accessory thyroid glands have been found in any 

 of the thyroidectomized animals examined by me in connection 

 with this work. 



An experiment to test the ability of thyroidectomized larvae 

 to withstand the deleterious effects of iodin in different con- 

 centrations was attempted. Iodin is only very slightly soluble 

 in water, but if the crystals are finely ground, a certain pro- 



