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THK AMKinCAN XATUEALIST [Vol. LV 



not fully known as yet (IS). One of these conditions is 

 the temperature as has l)een pointed out above. 



I will discuss briefly now the role of the hypophysis in 

 the growth and development of amphibians. The most 

 noteworthy fact seems to be the existence of a remark- 

 able resemblance between the functions of the amphibian 

 thyroid and hypophysis glands during the larval period. 

 If the hypophysis gland is extirpated in early embryonic 

 stages, the tadpoles stop to develop at a stage at which, 

 in normal tadpoles, metamorphosis begins. Growth, too, 

 is inhibited in the hypophysectomized. tadpoles (23, 24). 

 In a series of extremely interesting experiments Allen 

 (25) showed that both growth and development can be 

 restored to the hypophysectomized tadpoles, if the an- 

 terior lobe of the hypophysis of an adult frog is grafted 

 to such larvcT. Xo other part of the hypophysis when 

 grafted to the hypo])hysec'tomized tadpoles can restore 

 growth and dcxclopnit'iit. and it is certain, therefore, that 

 it is the anterior lobe of the hypophysis which controls 

 the growth and development of the larvcT. Iii tadpoles 

 the feeding experiments as made by P. E. Smith (26) 

 seem to corroborate the extirpation experiments. Feed- 

 ing of anterior lobe to hypophysectomized tadpoles in- 

 creases the rate of growth to such an extent that growth 

 becomes as vigorous as in normal larva?. Moreover, at 

 the time when the normal tadpoles metamorphose and 

 growth ceases for a time, the anterior lobe-fed hypophy- 

 sectomized tadpoles continue to grow and iinally attain 

 a size in excess of that of normal larva\ Ultimately, how- 

 ever, the growth of these larva' stops and before the size 

 is reached characteristic of the normal adult animal. 

 The etfect of feeding anterior lobe to normal larvffi is a 

 matter still under discussion at present. Smith (26) 



