THE EFFECTS OF HYPOPHYSECTOMY 



mized tadpoles (Allen, 1928). On the other hand, if salamander 

 larvae {Ambly stoma tigrinum) are hypophysectomized after the 

 development of the thyroid, their growth-rate (at least for a 

 period of eighteen weeks) is not significantly different from 

 that of normal larvae (Greenwood, 1924). Burns and Buyse 

 (1932) also hypophysectomized immature salamanders {A. 

 tigrinum, axolotl variety). Despite the operation, the animals 

 grew as large as normal adults. Such results differ from those 

 obtained in mammalian experiments. In very young rats 

 (less than four weeks old), some growth may occur for a short 

 time after hypophysectomy; in older rats (more than six 

 weeks old), growth ceases almost immediately after hypo- 

 physectomy. The excision of the pars buccalis in tadpoles 

 would correspond more to the hypophysectomy of the mam- 

 mal in utero — a feat which has never been accomplished. 

 Therefore, the experiments in which tadpoles were used can 

 hardly be compared with those in mammals. More compa- 

 rable are the experiments of Burns and Buyse, who hypophy- 

 sectomized immature salamanders which, however, finally 

 grew as large as normal salamanders. 



Regeneration of a limb or the tail occurs as readily in hypo- 

 physectomized as in normal axolotls (Kabak, 1931). 



Involution of the gonads or failure of the gonads to develop 

 as a result of hypophysectomy can be demonstrated more 

 clearly in immature or adult amphibia than in amphibian 

 larvae. Smith (1916) removed the pars buccalis of larvae of 

 R. boylei but found no constant change in the gonads as a re- 

 sult of the operation. Atwell (1932) performed the same 

 operation in tadpoles of R. sylvatica. The central part of the 

 ovaries of operated tadpoles contained large ovocytes sur- 

 rounded by interstitial tissue, whereas the cortical part con- 

 tained largely ovogonia. It is not clear from Atwell's report, 

 however, to what extent this histologic appearance differed 

 from the normal. Observations on the effect of hypophysec- 

 tomy on the genital tract of adult female toads have been 



[37] 



