No. G38] INTERNAL SECRETIONS OE AMPHIBIANS 195 



The rapidity with which these processes mny takf i.l.u'f 

 is one oi* the most remarkable features of the tlixioid 

 effect. Two normal larvtc of the species J. o/tacmn, tm- 

 instance, metamorphosed at an a^e of S() s .mikI iin ;i-- 

 ured 60 mm. at this time. Six other lar\;e of the s;iiii»" 

 brood were placed in an emnlsion of iodotlix riiii' ;it mm 

 age of 35 days, at which time they measuivd ;;o nun. on 

 the average. < >nc week later, at an au'(^ (.f oiilx iL' to 4;'> 

 days and a si/.r of l'4 mm., all luid nn'tam'ori.liosrd. 



47 days in one animal which was examined in sections, 

 the visceral skeleton had undergone all those complicated 

 changes through which the gill arches of the larva? de- 

 velop into the hyoid apparatus of the adult. The effect 

 of the thyroid hormone is quantitat Inc : the accclci'ation of 

 the amphibian metamorphosis incii ascs with increasing 

 concentration of the thyroid emulsion, a> shown in 

 Table I. 



TABLE I 



Qu \T T .TiVE Effect of the Thyroid Hokmoxe ix the Acceleration of 

 THE Metamorphosis of Amhiisinma nuinilatum 



ill one experiment the larva^ of Ambifsfoma ludciihit >nn 



