The Extirpatio7i of Glands in Tadpoles. 247 



found that by feeding in the same way that Gudernatsch had 

 done he produced the marked acceleration of metamorphosis 

 mentioned above, but that the germ glands and germ cells 

 remained unaffected, continuing their normal slow growth 

 and differentiation. Here again we have an influence exerted 

 on every organ except the germ glands. 



I think we are thus justified in saying that the germ glands 

 are not directly influenced by the thyroid gland. They neither 

 show acceleration with the administration of thyroid nor re- 

 tardation of development in absence of the thyroid. 



Investigations were made upon the effect of removal of the 

 pituitary gland of Rana pipiens. This was accomplished quite 

 readily by making an incision across the front of the head and 

 extending just beneath the pituitary gland. The latter was 

 then easily picked away with a needle. As a result of this the 

 tadpoles within eight days after the operation assumed a 

 bright silvery color throughout, due to the migration of the 

 black pigment cells from the epidermis, and to their marked 

 contraction throughout the whole body. This was true whether 

 these pigment cells were located in the skin or in the internal 

 organs. Metamorphosis was prevented just as truly as by the 

 removal of the thyroid gland. Owing to a very high mortality 

 brought about by the absence of the pituitary secretion, it was 

 impossible to study the later development of these tadpoles as 

 might be wished. Enough is known, however, to enable us to 

 say that metamorphosis is distinctly inhibited. This might 

 possibly be explained by the failure of the thyroid gland to 

 undergo its full development. Experiments are being con- 

 ducted now to determine this question. There is no doubt that 

 the absence of the pituitary gland caused the tadpoles to be 

 very susceptible to unfavorable conditions. This could not be 

 explained by injury produced, because many tadpoles that 

 have been operated upon failed to show the equal change and 

 continued to develop normally, reaching a size very much 

 greater than that of the silvery tadpoles. When these normal- 

 . appearing tadpoles were sectioned it was found that the pitui- 

 tary gland had not been removed in the operation, although 

 the injury had been just as severe in these cases as in those in 

 which the operation had been successfully carried out. There 

 was neither a serious retardation in growth nor an appreciably 

 large mortality. While both of these features were mainly 



