526 THYROID AND IODINE AND METAMORPHOSIS 



Other items to note will be changes in the mouth, the shape and size of the head, the ap- 

 pearance of the forellmbs, etc. 5y means of averages of these size changes, determine the 

 body proportions that show maximum response to the thyroid. 



While the tadpoles are exposed to the thyroid or iodine treatment for only a short 

 time (1 to 2 weeks) the final data should not be collected for from 1 to 2 weeks (or more) 

 after the cessation of the experimental conditions. Some of the tadpoles should be kept 

 until they achieve metamorphosis and the time of emergence from the water of the experi- 

 mentals and parallel controls should be noted. Normally Eana pipiens larvae will reach 

 stageg of metamorphosis in about 75 days after the eggs are fertilized, if kept at labora- 

 tory temperatures of 23°-25°C., fed well, and not crowded. 



Arrange your data in tabular form on preceding page, and illustrate with drawings or 

 photographs . 



DISCUSSION : 



It is not within the province of this Manual to carry an endocrine study beyond the 

 macroscopic examination. The relation of the thyroid and/or the pituitary gland to meta- 

 morphosis has been the subject of long and thorough studies. There are, however, other 

 embryological approaches to the problem which might bear investigation. These are sug- 

 gested in the form of questions, as follows: 



1. Will thyroid or iodine affect stages of development prior to the limb-bud stages, 

 or stages prior to the normal functioning of the host thyroid? Is there any ef- 

 fect on the blastula or gastrula or neurula, for instance? 



2.- The pituitary is known to have thyreotropic function, but which of these glands is 

 the ontogenetic precursor? 



5. What would be the effect on the embryos (larvae) following extirpation of either 

 or both the thyroid and the pituitary anlagen? 



h. What is the effect on them of grafting thyroids (or pituitaries) of the same and 

 of advanced ages into the tail blastemas of tadpoles. 



5. What is the effect of thyroid and of thyroidectomy upon the regenerative processes 

 of the larva? 



Some of these questions have been answered, but others should be. (See Beferences.) 



BEFERENCES : 



Adolph, E. F. , 1951 - "Body size as a factor in the metamorphosis of tadpoles." Biol. 



Bull. 61:376. 

 Allen, B. M., 1938 - "The endocrine control of amphibian metamorphosis." Biol. Bev. 15:1. 

 Bower, C. M., 1958 - "Growth rates of the hind limbs of Eana sylvatlca during normal and 



induced metamorphosis." Anat. Bee. 72: suppl. 99- 

 Clements, D. I., 1952 - "Comparative histological studies of the thyroid and pituitaries 



in frog tadpoles in normal and accelerated metamorphosis." Jour. Boy. Micr. Soc. 



52:158. 

 D'Angelo, S. A., A. S. Ckirdon, H. A. Charipper, 19^1 - "The role of the thyroid and 



pituitary gland In the anomolous effect of Inanition on amphibian metamorphosis." 



Jour. Exp. Zool 



Etkln, W., 1956 - "The phenomenon of amphibian metamorphosis. III. The development of 



the thyroid gland." Jour. Morph. 59=69. 

 Gudernatsch, J. F., I9I2 - "Feeding experiments on tadpoles." Arch. f. Ent. mech. 55:'+57. 

 Gunthorp, H., I952 - "Results of feeding thyroid glands of various vertebrates to tad- 

 poles." Physiol. Zool. 5:597. 

 Ingram, W. B. , 1929 - "Studies on amphibian neotony. I. The metamorp}josis of the Colorado 



axolotl by Injection of inorganic iodine." Physiol. Zool. 2:1^9. 

 Schneider, B. A., 1959 - "Effects of feeding thyroid substance." Quart. Bev. Biol. 114^:289. 

 Spaul, E. A., 1925 - "Iodine and amphibian metamorphosis." Proc. Zool. Soc, London. 995- 

 Swingle, W. W., I926 - "The effect on amphibian differentiation of feeding iodofibrln, 



lododestln, and iodogliadin." Anat. Rec. 5^:150. 

 Uhlenhuth, E. & H. Kama, I928 - "The morphology and physiology of the salamander thyroid 



gland. III. The relation of the number of follicles to development and growth of 



the thyroid in Amblystoma maculatum. " Biol. Bull. 5'+:128. 



