436 J. r. GUDERNATSCH 



July 11 Muscle-fed ones have the best developed hind legs, next the 

 ovary and adrenal-cortex ones which have short but very 

 strong legs, then adrenal-medulla, brain and spleen. 

 The color of the animals on the different diets is: control, 

 brown; muscle, dark brown; liver, dark greenish; spleen, 

 dark; adrenal cortex, very light brown; adrenal medulla, 

 dark broAvn; ovary, yelloAvish; thymus, dark; brain, brown. 



July 19 Muscle-fed ones begin metamorphosing. 



July 20 Ovary-fed ones begin metamorphosing. 



Thymus-fed have no signs of legs, spleen-fed only small buds. 



In this experiment the thj^roid treatment proved to be as 

 effective as in the experiments performed in 1911. Tadpoles that 

 had been fed on no other food than thyroid grew hind legs 9 days 

 after the feeding began and fore legs only 2 days later. Normally 

 several weeks would have elapsed between the appearance of the 

 hind and the fore extremities. When these thyroid-fed tadpoles 

 put out their anterior limbs and began to shorten their tail, they 

 were 18 to 20 days old, calculating from the date of hatching. 

 Normally they would take from 10 to 12 weeks to complete their 

 metamorphosis. 



The tadpoles fed on ordinary meat, muscle (fig. 1 d, 1 n), 

 showed distinct hind legs 44 days and fore legs 71 days later 

 than the thyroid-fed ones. The first individual in the muscle- 

 fed group to complete its metamorphosis was approximately 104 

 days old. 



Liver-fed tadpoles (fig. 1 a, 1 i, 1 x) show the best growth, al- 

 though their growth is only slightly better than that of the spleen 

 and thymus sets. Next to the thyroid group the liver-fed tad- 

 poles also showed most rapid progress in differentiation. They 

 grew hind legs 40 days and fore legs 49 days later than the thy- 

 roid group. The first liver-fed specimen to complete its meta- 

 morphosis was approximately 78 days old. 



The spleen- (fig. 16, 11) and thymus- (fig. 1 c) fed tadpoles 

 show almost parallel courses in growth and differentiation. Dur- 

 ing the first weeks of the experiments the spleen group ran a 

 little ahead of the thymus specimens. The members of both 

 groups became extremely dark in color during the course of the 

 feedings. At the approximate age of 104 days, when the experi- 



