148 E. UHLENHUTH. 



drowning. Fig. 3 shows No. 9 completely metamorphosed 134 

 days after the beginning of the experiment. 



Forty-three Days after the Beginning of the Experiment. Since 

 5 drops of iodine per 1,000 c.c. of water had no effect on meta- 

 morphosis, the iodine concentration was gradually increased and 

 has reached today 9 drops in No. 5 and 8 drops per 1,000 c.c. of 

 water in Nos. 4 and 6. Since it is believed that the alcohol used 

 as solvent of the iodine might have some influence, too, on the 

 animals, an equal number of drops of 95 per cent, alcohol is added 

 from now on to the water in the controls. 



Fifty -five Days After the Beginning of the Experiment. The 

 larvae of the iodine series did not show any sign of an approach 

 towards metamorphosis. Therefore the concentration of the 

 iodine (and of the alcohol in the control series) was further in- 

 creased and reached today 13 drops per 1,000 c.c. of water, a con- 

 centration of iodine more than 4 times the concentration sufficient 

 to cause growth of the limbs in tadpoles. 



Seventy-five Days After the Beginning of the Experiment. 

 The strength of the iodine solution was kept till today at 13 drops 

 of a 1/20 M solution of iodine per 1,000 c.c. of water; in addition 

 one larva (No. 5) was fed iodine crystals directly per mouth (i 

 crystal on the 57th, 63d, 68th, 7oth and 74th day after the be- 

 ginning of the experiment). Yet, in spite of these large amounts 

 of inorganic iodine being adminstered to the larvae, none of them 

 shows any signs of metamorphosis so far. 



From now on all larvae, controls as well as experimentals, are 

 kept in ordinary tap water, but the larvae, Nos. 5 and 6 of the 

 iodine series (No. 4 is used for a different experiment) are fed 

 crystals directly per mouth. 



One hundred and thirty-four Days After the Beginning of the 

 Experiment. The total number of 'iodine crystals fed to each 

 one of the iodine-fed larvae is now 25. This number of crystals 

 was fed to No. 5 during a period of 76 days and to No. 6 during 

 a period, of 59 days. These large amounts of inorgan'ic iodine 

 were incapable of accelerating metamorphosis. In both the con- 

 trols and the experimentals one larva has shed its skin, the iodine 

 larva (No. 6) be'ing now farther advanced than the correspond- 

 ing control. But No. 5, the other iodine-fed larva, is completely 



