412 



W. W. SWINGLE 



logically active and capable of inducing metamorphosis, pro- 

 vided their contained secretion could get into the blood stream. 

 Like the thyroid mechanism of axolotl, the glands of these larvae 

 seem to be rendered more or less functionless by an inhibiting 

 factor which prevents secretion of the hormone into the circula- 

 tion. Following transplantation, the inhibition apparently is 

 overcome by the acquisition of a new blood and nerve supply 



iM 



Fig. 1 Immature R. clamata larvae engrafted with the thyroids of extra large 

 neotenous tadpoles with hind limbs 11.6 mm. long, B, immature control animals 

 of A groups. X 2. 



in the new environment, because the absorbed secretion induces 

 metamorphosis. 



A modification of the experiment just recorded was attempted; 

 the thyroids of large neotenous larvae were engrafted intra- 

 peritoneally into other extra-season animals of the same size 

 and developmental stage. The idea was, that since the glands 

 of such individuals are physiologically active and capable of 



