Vol. XL V. November, 1923, No. 5. 



BIOLOGICAL BULLETIN 



IODINE AND AMPHIBIAN METAMORPHOSIS. 1 



W. W. SWINGLE, 

 OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY. 



Recently the claim has been made that the metamorphosis of 

 urodele larvae such as axolotl and amblystoma differs from that 

 of anurans in that transformation in the caudate amphibia is 

 independent of iodine and subject only to the influence of the 

 thyroid gland. Experiments are described in this paper which 

 invalidate this conclusion and indeed, render it impossible to 

 understand such a view. The role of iodine in metamorphosis 

 is also discussed, and evidence presented showing that the phys- 

 iologic response (metabolic changes) of mammals to thyroid 

 administration and the metamorphic changes of amphibian 

 larvae following iodine treatment are probably due to quite 

 different causes and hence not to be compared. 



Acknowledgement is due Mr. William Anderson for his labor 

 in iodizing the various compounds employed. 



The axolotls came from New Mexico, and were obtained 

 through the courtesy of Mr. J. N. Gladding of Albuquerque. 



I. EXPERIMENTS ON THYROIDECTOMIZED AXOLOTLS. 



The thyroid glands of eight animals were extirpated. One 

 larva was extremely large, measuring over a foot in length. The 

 remaining larvae averaged seven inches total length. Few tech- 

 nical difficulties are involved in removing the thyroid glands 

 from animals as large as the axolotl. The larvae were anesthe- 

 tized in chioretone solutions, placed upon their back under a 

 low-power binocular microscope, and the hyobranchial region 

 strongly illuminated. A median incision was made through the 

 skin and superficial muscles, extending from the posterior edge 



1 Part of the expense of this investigation was defrayed by a grant from the 

 Elizabeth Thompson Science Fund. 



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