METAMOEPHOSIS IN FROG LARVAE 541 



this series showed little or no change during the period of the 

 experiment, and when measured May 1, had increased their 

 length about 3 mm. 



It seems odd that after four months of total starvation, dur- 

 ing which growth and development were inhibited, the feeding 

 of thyroid extract should stimulate these starved animals to 

 undergo almost complete metamorphosis. 





si- 



p& - A 







a 



/ 



■ 



i •- ' > ■*■ Q 1 



U —"V^H Jrf^' M f ,' : 'T ( v" $"*'"'■ "o& 



V" l'")f .'■ >i f-v^'; i '■'■■'■ ' ■:• "'* i .",■ '■■ ■ **■ ~ t J ,- ''■'</ 





Fig. 12 Representative transverse section through the gonad of thyroid-fed 

 larvae which had almost completed metamorphosis. X 800. 



Fig. 13 Representative transverse section through gonad of control larva 

 for animal shown in figure 12. X 800. 



CONCLUSION 



The results obtained in the present experiment appear to 

 indicate that the thyroid gland has no intimate physiological 

 relation to the gonads and germ cells in the amphibia. By 

 feeding thyroid extract to frog larvae, great bodily changes are 

 brought about within a very few days; entire organs and systems 



THE JOURNAL OF EXPERIMENT \l. ZOOl OGY, VOL. 24, NO. 3 



