EFFECT OF IODINE ON LARVAE OF SALAMANDERS. 149 



larval and distinctly less far developed than the least advanced 

 control larva No. 2. 



One larva of each set was photographed today. Fig. i shows 

 the least advanced control larva No. 2, Fig. 2 the least ad- 

 vanced iodine-fed larva No. 5, and Pig. 3 the iodothyrine-fed 

 animal No. 9. While the latter animal 'is a completely metamor- 

 phosed terrestric salamander and has been so for several months, 

 both the control and the iodine-fed animal are larvae. The control 

 possesses, however, slightly shorter gills, its eyes are slightly more 

 bulging than those of the iodine-fed larva (not visible in the 

 photograph) and the ventral portion of the fin 'is greatly absorbed 

 as compared to the completely preserved fin of the iodine-fed 

 animal. On dissection the small intestine of the control, although 

 the control larva was larger than the iodine-fed larva, was found 

 to be shorter (308.5 mm.) than that of the iodine fed larva (387 

 mm.). 



In short 134 days after the beginning of the experiment the 

 least advanced control larva proved to be nearer metamorphosis 

 than the least advanced iodine-fed larva, although the latter was 

 kept, till the 75th day after the beginning of the experiment, in 

 iodine solutions of concentrations up to 13 drops of 1/20 M solu- 

 tion of inorganic iodine per 1,000 c.c. of water, and in addition 

 had received a total number of 25 iodine crystals during the last 

 76 days of the experiment. 



DISCUSSION. 



The experiments reported in this article fully confirm the ex- 

 periments reported in a previous paper, in which I showed tha^t 

 inorganic iodine does not enforce metamorphosis of normal larvae 

 of the salamander Ambystoma punctatitui!' The administration 

 of inorganic 'iodine, even if this substance be administered in com- 

 paratively large doses, is incapable of bringing about the amphib- 

 ian metamorphosis in those species in which the control of the 

 excretion of the thyroid hormone is of such a kind that no hor- 

 mone can escape from the thyroid before the end of the larval 

 period. 5 ' 8 



8 Uhlenhuth, E., /. Gen. Physio!., 1919. i, 473-482, and Am. \nt.. 1921, Iv, 

 193-221. 



