FEEDING EXPERIMENTS ON TADPOLES 463 



Experiment X 



Bufo vulgaris, Set III. Figure 9, a to r. Brought into the laboratory 

 May 21, 1912, size 18 to 23 mm, age unknown. Experiment started 

 June 5. Thirteen groups of tadpoles, 150 individuals in each, were 

 given food as indicated below; one group was starved. 



A part of this experiment corresponds to Experiment IV in 

 which several groups of tadpoles of Rana temporaria were fed 

 on thyroid for from 1 to 5 days respectively and afterwards put 

 on a vegetable diet. The Bufo tadpoles reacted very quickly to 

 the thyroid stimulus, but when the thyroid feeding was stopped, 

 they seemed to overcome the thyroid influence more readily than 

 any other tadpoles. The groups fed on thyroid from 3 to 5 days 

 (fig. 9, h to d) developed hind legs 5 days after the first feeding, 

 showing as in other experiments, that a 3 day feeding of thyroid 

 gland suffices to give the typical results. The 2 day group budded 

 the hind extremities on the 7th day and the 1 day group on the 

 11th day. These intervals approach close to those observed in 

 Experiment IV, which were 5, 6 and 14 days. The anterior ex- 

 tremities appear in the 5 day group 14 days after the first feeding 

 (in Experiment IV on the 10th day) and this group begins to 

 undergo metamorphosis on the 18th day. In the other, 1 to 4 

 day groups, the after-treatment with vegetable food seems to 

 check the hastened differentiation following the intake of thy- 

 roid tissue. They fuially do not go much faster than tadpoles 

 which had not received thyroid. It might thus appear as if the 

 Bufo tadpoles had a stronger resistancy against the thyroid stimu- 

 lus than the Rana larvae. This point is not entirely clear, how- 

 ever, since the former had not received any food before the thy- 

 roid feedings began, while the latter had previously lived for 50 

 days on muscle. As has been stated above, any meat diet before 

 or after the thyroid treatment is apt to render the animals more 

 susceptible to the thyroid stimulus than does starvation. 



The thyroid treated Bufo tadpoles do not reduce their size so 

 much as the Rana tadpoles, as before mentioned under Experi- 

 ment VII. 



THE AMERICAN JOrRNAl OF ANATOMY, VOL. 15, NO. 4 



