204 BENNET M. ALLEN 



a linear dimension of each volume value which may be roughly 

 compared with the average length measurement of the group 

 considered. While no claim is made for mathematical refine- 

 ment, especially in view of the marked change of form due to 

 metamorphosis, nevertheless the writer feels that a fair compari- 

 son may be made from the data at hand and that the results are 

 sufficiently striking to justify the conclusions drawn. These 

 figures speak for themselves and no further comment seems 

 necessary. 



There were no evidences of colloid deposition in the parathy- 

 roids of thyroidless tadpoles, even though the thyroid glands of 

 tadpoles in corresponding stage of development have a large 

 amount of colloid, and though they have reached an age and a 

 size corresponding to those of young toads long after metamor- 

 phosis — a stage when colloid is normally present in the thyroid 

 glands in large amount. Tliis shows quite clearly that in the 

 toad at least the parathyroid glands do not vicariously assume 

 the function of colloid production after removal of the thyroid 

 glands, as asserted by the authors mentioned in the discussion of 

 literature. There are, in fact, no peculiarities of any kind rec- 

 ognizable in the structure of the parathyroid glands of thyroidless 

 tadpoles. 



CONCLUSIONS 



1. Removal of the thyroid glands of Bufo causes a very marked 

 hypertrophy of parathyroid glands, so that they grow to many 

 times the volume attained by the thyroid glands of unoperated 

 specimens. 



2. There is no deposition of colloid in the parathyroid glands of 

 thyroidless tadpoles nor any other evidence of the assumption of 

 a vicarious relationship between the thyroid and parathyroid 

 glands. There are no noticeable histological peculiarities of the 

 parathyroid glands resulting from the removal of the thyroid 

 glands. 



