EFFECT OF IODINE ON LARV.E OF SALAMANDERS. 



TABLE V. 



EXPERIMENT II.: 30 DAYS AFTER BEGINNING OF EXPERIMENT. 



313 



As Tables III., IV. and V. show, the inorganic iodine had no 

 influence whatsoever on the development of the limbs. 



The relation between limb development and metamorphosis was 

 further tested in two experiments in which larvae of Ambystoma 

 maculatum at a more advanced stage were employed. Concerning 

 the action of iodothyrine, the results were in complete accordance 

 with those obtained in the larvae of Ambystoma opacurn; rapid 

 metamorphosis, but no influence on limb development was ob- 

 served. In each experiment one series was devoted to the study 

 of the influence of inorganic iodine; this substance likewise had no 

 influence on limb development, but unlike iodothyrine it did not 

 cause precocious metamorphosis. Both iodine experiments as 

 regards the influence of iodine on metamorphosis were described 

 in detail in a previous article (5) ; they will be only briefly reported 

 in this article. 



In Experiment III. the larvae were placed into iodine-free water 

 containing o.i gm. iodothyrine per 1,000 c.c. of water at an age of 

 20 days, at which date nearly all larvae had developed 4 toes in the 

 fore limbs and several had commenced to develop the first 2 toes 

 in the hind limbs. Thirty-three days after hatching i.e., 13 days 

 after the first administration of iodothyrine every one larva meta- 

 morphosed (as compared to 101 days in the controls), but in none 

 of them the number of toes was more than 7.5, and in one it was 

 only 6.0, this stage of limb development corresponding to the con- 

 trol series kept in iodine-free water without the addition of 

 iodothyrine. 



In Experiment IV. a smaller dosis of iodothyrine (o.oi gm. per 

 1,000 c.c. of iodine-free water) was administered. Precocious 

 metamorphosis was caused also by this dosis, but the development 

 of the limbs again remained completely unaffected as compared to 



