THYROIDECTOMY AND EARLY DEVELOPMENT 



321 



3. Select some embryos that show definite effect of thyroidectomy at a time when 

 metamorphic changes are beginning to appear in the controls, and treat them 

 with 1/1, 000,000 thyroxin to determine whether it is possible to compensate for 

 the loss of the thyroid gland in bringing the larvae through the critical stage of 

 metamorphosis. (Consult exercise on "Thyroid and Amphibian Metamorphosis". ) 



RANA' STAGE 17 



AMBYSTOMA' STAGE 31 



Infundibulum 

 Epiphysis 



Hypophysis 



THYROID ANLAGE 



Thyrod 



ENDOCRINE ANLAGEN AT 

 THE 5mm. STAGE (FROG) 



DISCUSSION: 



Thyroidless tadples will not generally go through metamorphosis. This stage in Rana 

 pipiens controls should be attained at about 75 days at laboratory temperatures, provid- 

 ing the food, space, and other factors are adequate. There is no doubt but that the 

 pituitary gland is closely related to the thyroid in function. The active element of the 

 thyroid gland is iodine, and this may be administered in different forms (e. g. , crystal- 

 line iodine, KI, or in thyroxin). Thyroidless embryos stiinulated by thyroxin may occa- 

 sionally surpass the controls in metamorphic changes. 



REFERENCES 



ALLEN, B. M., 1938 - "The endocrine control of amphibian metamorphosis." Biol. Rev. 13:1. 



BAUMAN, G. , 1936 - "Modifications des premiers stodes du developpement des oeufs de bactraciens anoures sans I'influence de 



la Thyroxine." C. R. Soc. de Biol. 121:1032. 

 BOWERS, C. Y. , A. SEGALOFF G B. BROWN, 1959 - "Factors affecting the thyroid gland uptake of 1-131 of the Rana catesbiana 



tadpole." Endocrin. 65:882-888. 

 HOSKINS, E. R. G M. M. HOSKINS, 1919 - "Growth and development of Amphibia as affected by thyroidectomy. " Jour. Exp. 



Zool. 29:1. 

 HUNT, E. G J. N. DENT, 1957 - "Iodine uptake and turnover in the frog tadpole. " Physiol Zool. 30:87-91. 

 LARSON, M. E. , 1927 - "The extirpation of the thyroid gland and its effects upon the hypophysis in Bufo americanus and Rana 



pipiens. " Sci. Bull. Univ. Kansas. 17:319. 

 STOKES, M., 1940 - "Early localization of the thyroid anlage' in Hyla regilla. " Proc. Soc. Exp. Biol. G Med. 45:681. 

 TAYLOR, A., 1934 - "Athyroidism in the salamander, Triturus torosus. " Jour. Exp. Zool. 273:153. 



