38 E. R. HOSKINS AND M. M. HOSKINS 



rium and swim rapidly toward the surface, their momentum en- 

 abling them to reach the air which they breathe in. This air 

 is soon expelled again and the process repeated. Not only do 

 the normal larvae which are later to become frogs use their lungs 

 in this manner, but the thyroidless animals which are to remain 

 in the larval state do the same. As they later become larger 

 their lungs become very large, extending to the posterior limit 

 of the body cavity. These older thyroidless larvae breathe in air 

 less frequently than they do at the time of normal metamor- 

 phosis, but when they are autopsied their lungs are always seen 

 to contain air. They are not dependent on their internal gills 

 for respiration, as was seen when one of them was placed in a 

 moist chamber. In this situation the animal lived for two days, 

 breathing irregularly. Ultimately it must starve, as it cannot 

 move about or feed as in normal circumstances. 



Intestines. As noted by Allen ('18), the intestinal tract of 

 the thyroidless larva does not shorten as does that of the normal 

 larva in metamorphosis, but continues to increase in length and 

 diameter with the growth of the animal. As shown in figure 

 35, the groove in the liver which is made by the gut persists 

 in all of the thyroidless larvae. The variability in the length 

 of the intestine has already been discussed (Allen, '18, p. 505). 



Adrenals. The adrenals in amphibia are, unfortunately, so 

 diffusely scattered along the kidney as to render impractical a 

 study of their size. In mammals, we have shown (Hoskins, '16) 

 that the size of the suprarenals tends to increase, with increase 

 in the size of the liver, kidney, and heart produced by changes 

 in metabolism that are in turn brought about by thyroid feeding. 

 Somewhat similar interrelations should exist in amphibia, al- 

 though these structures are not in quite the same condition as 

 in mammals. 



Skin. The only differences in the skin to be noted in our 

 various animals is that in many cases, although not in all, the 

 skin of the thyroidless larva tends to contain more pigment than 

 the normal amount, and these larvae thus appear darker than 

 the controls. The integumentary glands developed normallj^ 

 in thyroidless larvae. 



