IODINE AND AMPHIBIAN METAMORPHOSIS. 233 



The experiment shows beyond doubt that thyroidless urodele 

 larvae respond to iodized substances in precisely the same manner 

 as thyroidless and pituitaryless anurans. The importance of 

 iodine in the amino-acid and protein molecule in order to render 

 these substances effective in inducing metamorphosis is clearly 

 demonstrated. 



II. EXPERIMENTS ON LARVAL Spelerpes bislineatus. 



H. H. Wilder years ago ('99) called attention to Spelerpes as 

 a favorable object for experimentation. Unlike most urodeles, 

 the larvae of Spelerpes can be obtained at any season of the year 

 and are easily kept under laboratory conditions. The larval 

 life of this form has not been adequately investigated, conse- 

 quently little is known concerning it. I. W. Wilder ('22) has 

 been engaged for some years in studying the relation of growth 

 to metamorphosis but to date has published only a very brief 

 summary of the results. The data indicate a large range of 

 variation in the size and age of the animals at transformation, 

 with an average larval life of two years. 



Eighty animals were used in the experiment, varying in size 

 from 23 mm. to 53 mm. total length. They were separated into 

 four groups of twenty animals each, equal numbers of large and 

 small larvae being represented. One group of twenty animals 

 was kept in a large aquarium and given plenty of food. The 

 three remaining cultures were subdivided into smaller lots of ten 

 animals each and kept in glass containers in 250 cc. of tap water 

 w r ater through which compressed air bubbled constantly. Spe- 

 lerpes larvae soon die if kept in small amounts of water unless it 

 is kept cool and well aerated. Twenty individuals were reared in 

 tyrosine solutions representing 120 mg. per 250 cc. of water; 

 another twenty were kept in equivalent solutions of 3-5 dibrom- 

 tyrosine; twenty more in equal concentrations of 3-5 diiodotyro- 

 sine. The animals were fed sparingly during the experiment. 

 Once each week they were removed from the tyrosine solutions 

 and placed in large containers holding 6,000 cc. of water, plenti- 

 fully supplied with food and allowed to feed for thirty-six hours 

 after which they were returned to the solutions. 



The experiment began October 17. Thirteen days from the 

 date the animals were placed in the solutions, two large larvae of 



