PARATHYROID GLANDS OF THYROIDLESS LARVAE 203 



the thyroid, pituitary, and thymus glands (Allen, '18; Rogers, 

 '18, and Larsen, '19), no such reduction in size is indicated in the 

 present work. The number of specimens of this stage is too 

 small to have any significance upon this point. In general there 

 is a constant regular increase in the volume of the parathyroids 

 of the controls. The number of nuclei counted in maximum-size 

 sections shows the corresponding increase demonstrating that 

 the growth in size is a genuine growth in the amount of tissue, 

 not a mere loosening of the texture of the gland. Since counts 

 of the nuclei had to be made in a section of each of the four para- 

 thyroid glands of each specimen, it iseasy to see that the work of 

 counting becomes very laborious when one is dealing with the 

 large thyroidless tadpoles. Observations upon the other speci- 

 mens in which counts were not made showed that the parathyroid 

 glands were of equal density. For these reasons the count was 

 not carried further. In these two cases where counts were made, 

 there was such a large number of nuclei that the comparison 

 with the older metamorphosed controls was perfectly clear. 

 It is quite safe to say that the relative density of the para- 

 thyroid glands of thyroidless tadpoles is equal to that of the 

 parathyroids of the controls and that their much larger size in 

 the thyi'oidless tadpoles probably indicates that in these they 

 have a greater functional importance than in the controls. Even 

 though the average body length of the young Bufo controls, 

 studied in this work, was 50 per cent greater than the body 

 length of the thyroidless specimens, their parathyroid glands were 

 much less than one-fourth as large as those of the thyroidless tad- 

 poles. In comparing the large thyroidless tadpoles with the 

 young control tadpoles in the corresponding state of differentia- 

 tion, nos. 1 to 5, it is seen that the parathyroid glands of the 

 controls have less than one-fifteenth the volume of the thyroid- 

 less specimens. While the average body length of these controls 

 is as 10.2 mm. compared with 17.9 mm. 



In order to give a more accurate criterion for estimating the 

 relative average volume of the parathyroid glands of specimens of 

 different size and stage of development, the cube root of the 

 general average volume in each group is given. This would give 



