PLATE 1 



EXPLANATION OF FIGURES 



1 Surface view of the third vertebra of a normal control frog killed August 

 6, body length 21.5 mm. showing the irregular deposition of the calcium salts, 

 the deposition of calcium salts lateral to the centrum and the well developed 

 spinous process. 



2 Surface view of the third vertebra of a thyroidless tadpole killed October 

 14, total length 80 mm., body length 29 mm. showing the uniform deposition of 

 calcium salts, the well marked centers of calcification, the presence of a deposi- 

 tion of calcium salts in the rib, the total absence of a spinous process, and the 

 regular outline of the calcium salts in the centrum. 



3 Surface view of the third vertebra of a normal control frog killed August 



6, body length 21.5 mm. showing the heavy deposition of calcium salts on the 

 sides and ends of the centrum, and the deposition of salts lateral to the centrum 

 filling in the neuro-central suture. 



4 Surface view of the third vertebra of a thyroidless tadpole killed October 

 14, total length 80 mm., body length 29 mm. showing the heavy deposition of 

 calcium salts in the centrum, the marked centers of calcification and the lack of 

 deposition lateral to the centrum. 



5 Surface view of the third vertebra of a normal control tadpole having a leg 

 length of twelve millimeters, total length 52 mm. showing the uniform deposi- 

 tion of calcium salts in the centrum and neural arch before metamorphosis and 

 also the fairly well developed spinous process. 



6 Surface view of the third vertebra of a thyroidless tadpole killed February 



7, total length 123 mm., body length 43 mm. showing the increase in size, the 

 increase in the amount of calcification and the partial filling in of the neuro- 

 central suture and the dorsal bridge. 



7 Transverse section of the centrum and neuro-central suture of a normal con- 

 trol frog killed March 28, body length 56 mm., showing the large amount of peri- 

 osteal bone and osteogenic tissue. 



8 Transverse section of the centrum and neurocentral suture of a thyroidless 

 tadpole killed March 6, total length 102 mm., body length 40 mm. showing the 

 absence of the periosteal bone formation, the early stage of the hyalin cartilage 

 cells of the neuro-central suture and the small amount of endochondral ossifica- 

 tion in the centrum. 



582 



