4l6 BENNET M. ALLEN. 



possible that the pituitary gland might play the chief role in the 

 utilization of iodine by the body. This view is in the main based 

 upon the fact that tadpoles of Rana and Bufo, deprived of the 

 pituitary gland, fail to metamorphose in spite of the fact that 

 the thyroid glands remain intact and even though the body of 

 the tadpole reaches gigantic size. The removal of the pituitary 

 gland renders the thyroid gland as powerless to bring about 

 metamorphosis as though the thyroid gland were itself removed. 



It was shown by Swingle that metamorphosis could be pro- 

 duced in normal tadpoles by feeding them iodine. He likewise 

 showed that iodine feeding would produce metamorphosis even 

 in tadpoles deprived of the thyroid glands. Simultaneously 

 with the above work, the writer was carrying on the experiments 

 that form the subject of the present paper. They show con- 

 clusively that metamorphosis can be produced by iodine feeding 

 in tadpoles deprived of the pituitary glands. More striking 

 still is the demonstration of the fact that feeding iodine to tad- 

 poles deprived of both thyroid and pituitary glands can carry 

 them far in the process of metamorphosis, the attainment of 

 which was prevented only by the death of the tadpoles. 



In the light of all these facts, we are justified in drawing the 

 following general conclusions: 



With normal feeding, involving the intake of very minute 

 quantities of iodine, the presence of both the thyroid and pituitary 

 glands is essential to enable the animal to undergo metamor- 

 phosis. Unpublished data show quite conclusively that Rana 

 and Bufo larvae proceed to the same stages of limb growth in the 

 absence of the thyroid or of the pituitary gland or of both to- 

 gether. The administration of large quantities of iodine will 

 cause the tadpoles to undergo metamorphosis in the total absence 

 of the thyroid gland or of the pituitary gland or in the simul- 

 taneous absence of both thyroid and pituitary glands. It may 

 be found by later experimentation that iodine is not the only 

 factor that is capable of bringing animals to maturity. Investi- 

 gation along these lines is still in its infancy. Before this paper 

 appears in print, the writer expects to have under way more 

 extensive quantitative experiments that will determine the 

 reactions of normal, pituitaryless, thyroidless, and pituitary- 



