FEEDING EXPERIMENTS ON TADPOLES 



449 



TABLE 7 



A glance at table 5 will show that the tadpoles of 37 and 46 

 (or 35 and 44) days showed the slowest reaction to the thyroid 

 treatment. The possible reasons for this behavior were dis- 

 cussed above. 



Experiment IV 



Rana temporaria, Set II. Figure 2, a to n. 960 tadpoles hatched 

 on April 6 to 7, 1912, and fed on muscle until June 3. The experiment 

 started on June 5. 



This experiment confirmed the results of the two previous ones. 

 Tadpoles (fig. 2, a) which had lived for 50 days on an ordinary 

 meat diet were later affected by the thyroid stimulus as greatly 

 as animals fed only on a thyroid diet. The main object of this 

 experiment, however, was to ascertain how long the thyroid agens 

 had to be applied before results were noticeable, and furthermore, 

 whether or not it would be possible to counteract the thyroid in- 

 fluence after one or more days feeding. A great number of tad- 

 poles were reared on muscle and at the age of 50 days were di- 

 vided into groups of 80 individuals each. The different groups 

 were then fed on thyroid from 1 to 5 days and after this treat- 

 ment five of the groups were put on a vegetable diet (Elodea 

 canadensis) (fig. 2, / to i) and 5 others on muscle diet (fig. 2, c to e). 



One group (fig. 2, 6) was allowed to starve to test whether 

 hunger following a long period of feeding (over 6 weeks) would 

 bring about a quicker differentiation. 



Still another group (fig. 2, I) was kept in water in which small 

 pieces of thyroid gland were placed, but so arranged that the 



