GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 7 



less rapidly than the animals of the control group; those with 

 regenerated thyroids which grow at about the same rate as the 

 controls; and those which have normal jaws and muscles, but 

 are devoid of thyroid, and which grow more rapidly than the 

 normal animals. 



The growth rate of frog larvae kept in aquaria varies greatly, 

 and the most important factor in this is the kind and quantity 

 of food; but the size of the aquarium is very important, because 

 it is easier to keep large aquaria balanced than small aquaria. 

 The influence of the food and size of the aquarium is shown very 

 clearly by a comparison of the growth of our 1917 and 1918 

 animals. 



In 1917 fourteen series of extirpations were performed with 

 about 700 larvae. These were kept in small aquaria and fed 

 from April to the beginning of June upon a plant obtained from 

 a local aquarium supply dealer, and to this diet were added 

 occasionally cracker crumbs and bits of liver. In June the diet 

 was changed to spirogyra, and the animals were transferred to 

 larger aquaria. The growth rate rapidly increased when this 

 change was made. The average time of metamorphosis of the 

 control animals did not arrive until the first week in August. 

 Under optimum laboratory conditions R. sylvatica undergoes 

 metamorphosis in June or July. 



In 1918 the animals were exposed to the sun for an hour 

 or two each day. In each aquarium were placed small plants 

 and a layer of mud and old oak leaves from a pond of stagnant 

 water. The diet used in 1918 was composed principally of algae 

 found floating on the surface of a stagnant pond. Taken with 

 the algae were large numbers of small crustaceans which the 

 tadpoles may have eaten after the crustaceans died in the aquaria. 

 Only small amounts of the algae should be put into the aquarium 

 at a time, because if added in large amounts it will die and poison 

 the tadpoles. In our 1918 experiments the animals grew much 

 more rapidly than did those of the previous years. Whereas 

 in 1916 and 1917 the larvae required a minimum of three months 

 to reach their maxjmum size and begin metamorphosis, the 

 minimum time required by the 1918 larvae for this was only 



