RELATION OF GLANDS TO IODINE AND METAMORPHOSIS. 415 



a whole have shrunken appreciably together with the shrinkage 

 of the body as a whole; but not proportionately as much. In 

 the iodine-fed tadpoles the colloid masses show a slightly greater 

 average diameter than do those of the normally fed specimens. 

 These facts do not seem especially significant. The slight in- 

 crease of the colloid masses and the actual decrease in the dimen- 

 sions of the gland roughly counterbalance one another. It is to 

 be admitted that the number of specimens is small but it is large 

 enough to demonstrate that no striking changes in the size of 

 the thyroid glands and of their colloid content in pituitaryless 

 tadpoles result from iodine feeding, at least, not within the 

 stages and time limits of the experiment. It will be interesting 

 in future experiments to test whether feeding iodine at early 

 stages prior to the normal time of colloid formation would cause 

 it to appear precociously. 



In a paper upon the "Development of the Thyroid Glands of 

 Bufo and their Normal Relation to Metamorphosis," Allen 

 (in press), a study was made of the relation of the growth of the 

 thyroid gland to the growth and metamorphosis of Bufo tad- 

 poles. The stages used are a trifle more advanced than those 

 used in this experiment. It appears, however, that the thyroid 

 glands are of about the same size in their early stages in pituitary- 

 less tadpoles as in normal tadpoles and that the colloid begins to 

 form at the same time in both. 



SUMMARY AND CONCLUSIONS. 



At the beginning of this paper, attention was called to the 

 fact that the growth of the thyroid glands and the accumulation 

 of colloid in them are retarded by the removal of the pituitary 

 gland. Rogers and Larson have both shown that the removal 

 of the thyroid gland causes an hypertrophy of the pituitary 

 gland (Rogers, '18, anterior lobe; Larson, '19, anterior and inter- 

 mediate lobes). It would be premature to offer an interpre- 

 tation of these facts but they seem to justify the hypothesis that 

 these glands are closely interrelated. The writer has for several 

 years favored the hypothesis that the thyroid gland may, largely 

 at least, play the role of a storage organ for the iodine of the body, 

 at the same time controlling its distribution. It even seems 



