EFFECT OF IODINE ON LARVAE OF SALAMANDERS. 



Experiment I. One egg mass of Ambystoma maculatum was 

 collected on April 18, 1920. The eggs were not only freed from 

 the general mass of jelly, but also the individual egg envelopes 

 were removed, in order to assure ready access of the iodothyrine 

 and iodine to the developing embryos. 



Beginning of the experiment: 28 embryos selected; 9 of them 

 placed into iodine-free water (10,000 c.c. H 2 O, 0.16 gm. Na,CO 3 , 

 0.04 gm. K 2 CO 3 , 0.4 gm. MgSO 4 -7H 2 O, 0.6 gm. CaQ 2 ), 9 into 

 iodine (2 drops of a 1/20 M solution of inorganic iodine per 1,000 

 c.c. of iodine-free water) and 10 into iodothyrine (o.oi gm. Bayer's 

 iodothyrine per 1,000 c.c. of iodine-free water). In all embryos 

 the first four visceral arches are formed ; the fore-limb rudiments 

 not yet differentiated from the pronephridial protuberance; no 

 hind limbs. 



The concentration of the inorganic iodine was increased to 8 

 drops per 1,000 c.c. 5 days, decreased to 6 drops 7 days, and de- 

 creased to 4 drops ii days after the beginning of the experiment. 



Sixteen days after the beginning of the experiment: Neither the 



TABLE I. 



EXPERIMENT I.: 16 DAYS AFTER BEGINNING OF EXPERIMENT. 



iodine nor the iodothyrine had produced any influence on the de- 

 velopment of the limbs (see Table I.). 



Tzventy days after the beginning of the experiment: The con- 

 centration of the iodine is decreased to 3 drops per 1,000 c.c. of 

 water, the concentration of the iodothyrine increased to o.i gm. 

 per 1,000 c.c. of water. 



Tzventy-seven days after the beginning of the experiment: Hind 

 limbs commenced to differentiate into toes ; but neither iodothyrine 

 nor iodine accelerated limb development as compared to limb de- 

 velopment of controls kept in iodine-free water (see Table II.). 



