EFFECT OF IODINE ON LARV.E OF SALAMANDERS. 147 



fin on ventral and dorsal side of tail, eyes not bulging out) and 

 No. 3 was neotenous (a sex mature male whose cloacal lips were 

 swollen and warty). These 3 larvae served as controls. 



No. 4 measured 184.9 mm - 5 No. 5, 158.5 mm.; and No. 6, 

 214.0 mm. All 3 larvae were completely larval; No. 6 was a sex 

 mature male. This set of larvae was used for the iodine experi- 

 ment. 



No. 7 measured 179.8 mm.; No. 8, 154.2 mm.; and No. 9, 

 184.5 mm - Again each animal was completely larval ; the third 

 one, however, presented no external sign of sex maturity (it was 

 probably a female). This set was used for the iodothyrin experi- 

 ment. 



It will be noticed that each larva of each set was comparable to 

 a corresponding larva of the two other sets, as regards size and 

 stage of development. The larvae selected for the iodothyrin ex- 

 periment, however, were smaller in average than the larvae of the 

 two other sets. This selection was made in order to be sure that 

 in case the larvae kept in iodothyrin should metamorphose before 

 the other larvae their earlier metamorphosis was not due to a more 

 advanced stage at the beginning of the experiment, but to the 

 specific effect of the iodothyrin. 



On December 9, 1920, the larvae of the second set (Nos. 4, 5, 6) 

 were placed into an iodine solution containing 5 drops of a 1/20 M 

 stock solution of inorganic iodine (in 95 per cent, alcohol) per 

 1,000 c.c. of water, while the larvae of the third set (Nos. 7, 8, 9) 

 were put into water containing o.i gm. of Bayer's iodothyrin per 

 1,000 c.c. of water. The larvae of the first set (Nos. i, 2, 3) 

 served as controls. 



Thirteen Days after the Beginning of the Experiment. The 

 controls and the larvae of the iodine experiment do not show any 

 changes, in particular no signs of metamorphosis. Every one of 

 the three larvae kept in iodothyrin was found this morning to have 

 shed its skin for the first time. 



These three larvae absorbed the gills very quickly, moulted sev- 

 eral more times in rapid succession, and 25 days after beginning 

 of the experiment had reached the stage at which the larvae must 

 be removed from the water and put on land, in order to prevent 



