6G() 



C. M. LAPIERE AND J. GROSS 



to 



--0 o--. 



Starved 

 Controls 



Thyroxin 

 ^ Treated 



50 



DAYS 



Thyroxin 



Fig. 2. Decrease in tail length of tadpoles treated with thyroxin as a func- 

 tion of time of exposure to the hormone. Controls were starved, since thyroxin- 

 treated animals ceased feeding. 



Comparing tail fin and back skin in the resting state, collagen 

 concentration is fourfold higher in the latter, with free proline and 

 noncollagen protein concentration about twice as high. There is 

 some resorption of collagen from the back skin, associated with the 

 change in shape and organization which occurs in this area during 

 metamorphosis (Kemp, 1961). 



