METAMORPHOSIS IN FROG LARVAE 



535 



fed and algae-fed animals are very marked. The experimental 

 animals are far ahead of the control tadpoles in somatic develop- 

 ment. 



The alimentary tracts of both control and thyroid-fed animals 



Fig. 6 Photograph of thyroid-fed and control Rana catesbiana larvae, 

 thyroid 23 days. 



Fed 



were measured. The average length of the tract from oesoph- 

 agus to cloaca in the experimental larvae was 100 mm. In 

 all the thyroid-fed animals, the shape of the gut was very similar 

 to that of the adult. Figure 8 shows that the gut had differ- 

 entiated into the divisions characteristic of the frog, and had 

 a well developed stomach, a small and a large intestine. 



In the control animals, the average length of the spiral gut 



