EFFECTS OF EXTIRPATION OF THYROID GLAND 573 



correspondence with the fact that the former have outstripped 

 the latter in body length. 



Another very interesting phase in comparing the vertebrae 

 of the thyroidless and control tadpoles is the nature of the 

 deposition of the calcium salts (figs. 1, 2, and 5). Figure 5 

 represents the third vertebra of a normal control tadpole killed 

 before metamorphosis, total length 52 mm., body length 23 

 mm. when the hind legs have reached a length of only twelve 

 millimeters. Especially to be noticed at this early stage is the 

 uniformity of the deposition of calcium salts throughout the 

 neural arch and the centrum. In the control frog killed August 

 6 (fig. 1), body length 21.5 mm. the vertebra appears quite 

 different, the cartilage cells have been invaded by the osteo- 

 blastic tissue and a large part of the calcium salts have been 

 eroded away or completely absorbed. The centers of deposi- 

 tion appear more plainly marked than in the earlier stages and 

 are especially noticeable near the ends of the neural arch as 

 we approach the neuro-central suture and the dorsal bridge. 

 Heavier deposition is also noticed in the centrum and in the 

 transverse process some distance out from their point of union 

 with the neural arch. The same irregularity of deposition as 

 was noticed throughout the vertebra is also to be observed in 

 the centers of deposition. In other words there is a clumping 

 together of the calcium salt spicules giving us what we might 

 term small centers of deposition within larger centers. The 

 same thing is true of the centrum. Its outline is more or less 

 irregular, the deposition is not uniform, and it is confined almost 

 entirely to the ends and lateral portions as clearly shown in 

 figures 1 and 3. The dorsal and ventral sides contain a very 

 small amount of calcium salts and are easily shattered in free 

 hand sectioning. The most striking thing in the case of the 

 controls is the deposition of salts lateral to the centrum which 

 is peristent in all forms studied after the time of metamorphosis 

 and which is not at all shown in the thyroidless tadpoles. In 

 the thyroidless animal killed February 7, total length 123 mm., 

 body length 43 mm. we see that a great part of the neurocentral 

 suture has been filled in by deposition lateral to the neural 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 3 



