FEEDING EXPERIMENTS ON TADPOLES 459 



The difference between the rates of growth of the two sets is 

 not marked^ there may be a Httle faster growth in the set fed on 

 neural hypophysis. The tadpoles fed on glandular hypophysis 

 (fig. 5 b, 5 d) show decidedly better differentiation and gradu- 

 ally become less pigmented than those fed on neural hypophysis 

 (fig. 5 e). 



Experiment VII 



Bufo vulgaris, Set I. Figure 8, a to d. Hatched April 10 to 20, 

 1912, and the feeding began May 6. 



The experimental data are as follows : 



May 5 The feeding began. 



May 11 All the thyroid-fed specimens have hind legs and the frog 

 shape is noticeable. They were fed only four times. 



May 18 Thyroid-fed animals have developed fore legs. 



May 22 Algae were placed in with the thyroid-fed tadpoles. 



June 18 Last thyroid-fed ones die. 



June 20 Thymus-fed ones have hind leg buds. 



June 24 Control animals have hind leg buds. 



July 1 1 The muscle-fed tadpoles have the best differentiated hind legs. 



July 14 Muscle-fed animals grow fore legs. 



July 20 The first metamorphosis in muscle-fed group. The control 

 still have very small hind leg buds. Thymus-fed animals 

 have their hind legs still drawn close to the body. 



This experiment introduced a new species into the study, Bufo 

 vulgaris, yet the results, as one might have expected, are essen- 

 tially the same. The thyroid-fed group (fig. 8, d) showed their 

 usual precocious differentiation, their decrease in size is not as 

 marked as in the Rana species. The thymus-fed group (fig. 

 8, c) did not grow much faster than the muscle-fed ones (fig. 8, h) 

 and towards the end of the experiment they actually fell behind 

 in size, yet they showed little, if any, differentiation at the time 

 of the first metamorphosis of the muscle-fed tadpoles. A con- 

 siderable number of the thymus group died when they reached 

 a length of about 21 mm (status thymicus, thymus death). 



