574 GEORGE S. TERRY 



arch rather than by deposition lateral to the centrum as was 

 the case in the controls above mentioned. 



In comparing the thyroidless tadpole at the time when 

 metamorphosis should normally take place with a normal 

 control of the same age we see that the amount of calcification 

 in the one corresponds very closety with that in the other, but 

 especially to be emphasized at this stage is the fact that the 

 process of ossification in the thryoidless animal is greatly de- 

 layed. The cartilage cells appear to be almost completely 

 calcified but the process of absorption of these salts appears to 

 be almost stopped. The same spicular arrangement of the 

 granules can be observed but they are more or less fused together 

 and as a result they appear more uniform in their distribution. 

 The centers of deposition have a very definite and regular out- 

 line and are clearly marked off from the rest of the vertebra 

 (figures 2 and 4). Further differential points observed were 

 the presence of a heav}^ deposition of salts in the rib and their 

 uniform distribution in the centrum. One also notices in the 

 operated tadpole killed October 14, total length 80 mm., body 

 length 29 mm. that there is an absence of deposition lateral 

 to the centrum and that the line of separation between the 

 neural arch and the centrum is very definite. 



In the specimen killed seven months past the period of meta- 

 morphosis (fig. (5) I have failed to observe any striking changes 

 over the specimen above described other than a gradual de- 

 velopment of the vertebra consisting of an increase in size, an 

 increase in the amount of calcification and a partial filling in of 

 the dorsal bridge and the neuro-central suture. The neuro- 

 central suture is almost closed in the first and second vertebrae 

 especially on the anterior side, while the length of the dorsal 

 bridge has been greatly reduced. The centers of deposition 

 are still persistent but are much less prominent due to the heav- 

 ier deposition of salts in the other parts of the vertebra. 



The next point of interest is a comparison made in the dorsal 

 bridge region of the vertebra. In the case of the operated 

 tadpoles the development of the cartilaginous bridge is greatly 

 delayed. In the normal control tadpoles the spinous process 



