IODINE AND AMPHIBIAN METAMORPHOSIS. 



241 



readily adapt themselves to the changed environment.^ Animals 

 captured in the autumn generally pass the winter and spring as 

 tadpoles. 



September 13, 1922, a large number of larvae were collected 

 and eighty tadpoles of approximately equal size and develop- 

 mental stage were selected and divided into four groups of twenty 

 individuals each. One group was fed tyrosine, another ordinary 

 tadpole food such as spirogyra and insect larvae, the third lot 

 received dibromtyrosine and the fourth group diiodotyrosine. 

 A fifth culture of animals, forty in number, of varying size and 

 developmental stage was kept in large glass aquaria and fed 

 quantities of alga?. Each culture except the fifth was further 

 subdivided into lots of five tadpoles each, and placed in 250 cc. 

 of tap water containing 120 mg. of the tyrosine compounds. 

 Each evening the animals were transferred to large jars contain- 

 ing 10,000 cc. of tap water and plentifully supplied with alga.'. 

 This procedure was considered necessary in order to rule out the 

 starvation factor since tadpoles can not exist indefinitely on 

 tyrosine alone. 



The animals obtained the tyrosine compounds by two methods: 

 through the alimentary tract, and by absorption through the 

 skin. Most of the tyrosine goes into solution after a short time, 

 hence the larvae probably obtain most of this substance through 

 the skin. This is certainly the manner in which Spehrpes larvae 

 obtain the tyrosine and its iodized and brominated compounds. 



Table I. gives the average measurements of the animals at 

 the beginning and end of the experiment. The figures are averages 

 based upon measurements of fifteen animals of each culture. 



TABLE I. 



Thirteen days from the beginning of the experiment a marked 



