120 W. W. SWINGLE 



into older larvae. These results are interesting when it is recalled 

 that under normal conditions the larvae of the bullfrog require 

 approximately two years to complete metamorphosis. Fully 

 differentiated legs do not appear usually until the larvae are al- 

 most full-grown in regard to size and over a year old. Hence, 

 when hind limbs are induced to grow to a length of 14 mm. in 

 immature tadpoles of 50 mm. total length by transplantation of 

 the anterior lobe of the hypophysis, and such growth occurs 

 within forty days, it is readily seen that the changes induced are 

 indeed marked. The effects upon metamorphosis following trans- 

 plantation of the thyroid of adult frogs are very much more 

 rapid, and more marked in every feature of the reaction than 

 those following transplantation of the anterior lobe of the pitui- 

 tary. Grafts of the anterior lobe "activate" the physiologically 

 inert gland of immature larvae. 



These experiments on the transplantation of the anterior lobe 

 of the hypophysis and the thyroid gland are not discussed in the 

 present communication, and are mentioned here in order to show 

 that my experiments along this line, together with those recorded 

 here, were begun simultaneously with and independently of the 

 closely similar work of Prof. B. M. Allen, of the University 

 of Kansas. Professor Allen has recently published a brief state- 

 ment of his results in Science (vol. 52, no. 1342, 1920). Our re- 

 sults are in essential agreement, differing merely in such minor 

 matters as technique, frog species used, and whether homo- or 

 heteroplastic transplants were utilized. 



MATERIAL AND METHODS 



Allen used normal, pituitariless and thyroidless tadpoles of 

 Rana pipiens and made use of homoplastic grafts only; my own 

 material consisted of the neotenous larvse of the bullfrog with 

 glandular material from several frog species; i.e., the grafts were 

 both homo- and heteroplastic in nature. 



The tadpoles used, in the majority of the later experiments, 

 were caught in the vicinity of New Haven and all came from the 

 same pool. The average size was 55 mm., from snout to tip of 

 the tail ; most of the animals had minute hind-limb buds. Dur- 



