THE PHENOMENA OF MUTATION 197 



metamorphosis, but the body was also shorter. 

 There is some reason therefore for concluding that 

 actual reduction in size of body occurs as the result 

 of metamorphosis induced by thyroid feeding. As 

 in the other case the skin and opercular membranes 

 were distended by liquid beneath them. 



The total period of the change in this second ex- 

 periment was ten days. 



I conclude that the amount of thyroid eaten was so 

 excessive as to cause pathological conditions as well 

 as precocious metamorphosis, so that the animals died 

 without completing the process. 



On June 10 I still had four tadpoles which had 

 never had thyroid, but only pieces of meat, earth- 

 worm, or fish. These were very much larger than any 

 of the others, were active and vigorous, and the 

 largest one showed small rudiments of hind-legs, the 

 others none at all. 



