On Amphibian Metamorphosis and Internal Secretions. 43 



1/100 solution. In the 1/10 solution the animals refused to feed at all. 

 One (the smaller) died after one day. The other was more sluggish than 

 normal animals. It showed distinct reduction of the gill-filaments after 

 3 days. The filaments were nearly absent after 5 days ; on this day 

 the solution was diluted to 1/12, as the animal seemed ill at ease. On 

 the eleventh day mere stumps of gills were left, and the tail-fin had been 

 nearly resorbed. The animal was poorly, not reacting to stimuli properly, 

 and on the twelfth day it was dead. The saturated solution contained 

 - 076 mgrm. of iodine per litre. 



Another series of experiments was started on January 26, 1920. Unfor- 

 tunately, it had to be discontinued after 16 days, owing to the ill-health of 

 Miss F. Peterson, who kindly helped with the work, and to whom grateful 

 acknowledgment is made. Twelve sets of four animals were taken, there 

 being two lame of S. maculosa and two of Triton vulgaris in each lot. These 

 were distributed as follows, according to temperature and to strength of 

 iodine solution : — 



Temperature. 



Strength of solution (in dilutions of a solution of iodine 

 saturated at room-temperature). 



1. 



2. 



3. 



4. 



A. 26° C 



B. 17°-18° C 



C. 2 3 -5° C 



1/20 

 1/20 

 1/20 



1/50 

 1/50 

 1/50 



1/125 

 1/125 

 1/125 



Control. 



In Series C no animals metamorphosed during the 16 days. In Series B 

 five metamorphosed after an average time of 11*6 days. In Series A five 

 metamorphosed after an average time of 6 days. This shows a very decided 

 retarding effect of low temperature upon metamorphosis. 



All animals were here kept in the same volume of water, so that only two 

 variables affecting gill-size remained. High temperature was found to favour 

 gill-development, while high iodine-concentration had the reverse effect. This 

 was well brought out in the results. The gills of those kept at 26° C. could 

 be arranged in a graded series according to size, the controls having the 

 largest filaments, those in the 1/20 solution the smallest. Those kept at 

 2°-5° C. also showed a series which was identical, except for the fact that it 

 started at a much lower level ; in fact, the gills of the controls at the low 

 temperature were slightly smaller on the average than the gills of those kept 

 in the 1/20 solution at the high temperature. The 17°-18° C. series was 

 intermediate, but rather nearer, as would be expected, to the high-temperature 

 series. 



