598 IODINE AND THE THYROID. Ill 



April 20, 1919. Controls: Length 25 mm. Limbs tiny epithelial buds as yet 

 imdifiFerentiated . 



Culture 1. — Length 26 mm. Legs small but perfectly developed. Pigmenta- 

 tion dark. Animals well nourished. 



Culture 2. — Length 29 mm. Very large, well nourished animals. Limbs 

 large. Fore limbs just visible under the skin. Pigmentation dark. 



Culture 3. — Length 23 mm. Legs 7 mm. long. Pigmentation light. Animals 

 very sluggish. Fore limbs easily visible under the skin. 



Culture 4. — Length 26 mm. Hind legs 9 to 10 mm. long. Tail shrinkage ap- 

 parent. Fore legs through skin on side in three animals. Pigmentation dark. 

 Animals sluggish. 



On this date the larvae left in the pool were examined again. The average 

 length was 13.5 mm. No limb buds were visible. Pigmentation slightly lighter 

 than that of the laboratory controls. 



April 27, 1919. Controls: Length 26 mm. Otherwise no change. 



Culture 1. — Lengtii 28 mm. Limbs larger and better developed than those 

 of controls. 



Culture 2. — Length 31 mm. Legs well developed otherwise no change. 



Culture 3. — Length 23 mm. No change, except an increase in the size of the 

 legs. 



Culture 4. — Length 27 mm. Fore legs through skin in several animals. Hind 

 legs very large. 



Animals in the pool were again measured. The average length was 15 mm. 

 Tiny epithelial hind limb buds present. No differentiation yet. Lightly pig- 

 mented. Animals well nourished and active. The experiment was abandoned 

 May 1, 1 month and 10 days from the date of the first iodine feeding.^ 



Discussion of Experiment 1. 



Metamorphosis. — ^The effects upon metamorphosis of feeding known 

 quantities of iodine in progressively stronger concentrations is ob- 

 vious from this experiment and needs only brief mention here. It 

 is clearly shown that the rate of metamorphic change in Anuran larvae 

 depends upon the amount of iodine the animals receive; the stronger 

 the concentration, the more rapid the change from larval to adult 

 condition. Iodine even in such minute quantities as Culture 1 



^ Though no iodine was fed after May 1, and but little food given all the 

 animals of Cultures 3 and 4 completely metamorphosed by May 17. Seven 

 larvas of Culture 2 had transformed by June 1. Two animals from Culture 1 

 metamorphosed June 10. None of the control tadpoles has yet completed 

 metamorphosis. 



