I3O W. W. SWINGLE. 



between the controls and thymus-fed animals either in regard to 

 body length, shape or stage of development. Before the experi- 

 ment was discontinued the larvae of both groups of animals were 

 measured. The controls measured in length 41 mm., the thymus- 

 fed animals 39.5 mm. 



In this series of larvae, as in the two previous series, thymus 

 feeding certainly did not accelerate growth. 



On November i, another set of Rana catesbiana larvae were 

 obtained, and all larvae of 75 mm. in length were selected for 

 thymus feeding. There were twelve 75 mm. larvae. They were 

 divided into two groups of six each for controls and thymus 

 feeding purposes. The diet of both groups was similar to that 

 given to the larvae of the previous series. 



November 10 the animals of both control and thymus-fed 



e 



groups were measured. The controls averaged 83 mm. in length ; 

 the thymus-fed larvae 85 mm. The limb buds of both groups 

 were very small. No other differences in the two groups were 

 noticed. 



December 9, the larvae of both groups were again measured. 

 The controls averaged 89.5 mm. The thymus-fed larvae averaged 

 90.5 mm. Pigmentation, body shape, were the same in the 

 animals of both groups. 



December 23, the animals of both control and thymus-fed 

 groups were again measured. The controls averaged in length 

 92.5 mm., the thymus-fed larvae 93 mm. The limb buds of 

 both groups appeared to be of about the same size and stage of 

 development. 



The experiment was discontinued at this time. 



It was observed in this series that the thymus-fed larvae aver- 

 aged slightly more in length than the controls. The differences, 

 however, are very small. 



A last series of feeding experiments with powdered thymus was 

 started November 17, 1915. Eighty small tadpoles (species 

 not determined), averaging 17 mm. in length and without limb 

 buds, were brought to the laboratory on this date. Thirty were 

 selected and treated similarly to those of the earlier experiments. 

 These animals were fed thymus from November 17 until Decem- 

 ber /. Upon this date the tadpoles of both control and thymus- 



