No. G3S] INTERNAL SECRETIONS or AM I'll / HI 213 



consequently did not metamor})li()>('. ilic cnl<»i-;ition ot' tlio 

 skin advanced to a stage very similar to that of ;ni adult 

 animal. On the other hand if yoiiuu l;n-\;r of J. oparinn 

 are made to metamorphose precociously l.y menus of the 

 application of iodothyrine, metamorphosis takes place, 

 while the color pattern remains in an carlv larval stage. 

 Through the ol)servatious of Cop.. ( ;!.-)) it has become 

 lamwn that othrrwix- c-omph'tely metamorphosed indi- 

 viduals of the speeies J. /Ifn-'nnnii may •■xhihit either a 

 larval conditi.)n of the tongue or larval" chai-aeters of the 

 palatal teeth or larval characters in both the tongue and 

 the palatal teeth. 



In nature it is not uncommon that the sex glands of 

 salamanders develop to complete maturity while the rest 

 of the organism remains in a lar\-al stage iH). This 

 phenomenon, known b\- the name of neoten.x. illusti'ates 

 that the sex organs can develo}) in the al)sence of the thy- 

 roid function. The same fact has been shown in the 

 larvae of anurans by B. M. Allen and his coworkers. In 

 thyroid-fed frog larvfr, which have undergone precocious 

 metamorphosis, the sex (n-gans do not seem to be further 

 developed than those of normal lar\a' of the same auc 

 (3). Moreover, if the thyroid is ivmoved fi-om the lai va' 

 and metamorphosis inhibited, the sex organs di^xt'lo]) at 

 the same rat(^ as in normal larva' cJl). lloskin- (i^-) 

 and Allen (I'l) showed that the testiele of thyroi.leetom- 

 ized tadpoles may develop ripe spermato/.oa. 'i"he>e 



germ plasm is independent of the soinatic i)lasm, in the 

 Weismannian sense. The characteristic feature of the 

 amphibian development is not the independence of the 

 germ ])lasm fi'om the sonnitic plasm, Imt the imle- 



due to the fact that the development of each of these 

 groups is conti'olled by substances ditfereiit from those 

 controlling the other groups, and that each of these sub- 

 stances sepai-ately ma\- l)e supplied to or withheld from 

 the organism either by the experimenter or l)y conditions 



