No. 638] INTERNAL SECEEriOXs or AM I'll /HI A. \> 211 



the thyroid action at least in salaniaiulcrs and iu;iy. uiidtT 

 certain conditions, occur in the ahsmcc of tliis ;ic-li()ii <ir 

 not occur in the presiMicc of ii. 1 have pointed out in 

 former articles (18) that ;iiiioiiu- the iiiaii\- chaiiiics occur- 

 ring during the sakmaiidcr mctainoi-pliosis thci-c nro two 

 which seem to be particulai'l>- closely related to the tliv- 

 roid action, namoly the Hrst shiMhliii- of the >kin ;nid the 

 redncti..u of the -ills to mere stubs. While the >ucr..sHoii 

 of all the other chau-es eiiuuiernted alM.ve >eeuis ex- 

 tremely variable, the or.ler in which the lirst moult and 

 the reduction of the -ill., follow en.-li other could not h:' 

 chauovd .-IS yet hy any of the pi-ocedures emph^ved. inn>- 

 nmch a> the sheddin- of the skin always is followed l.y 

 the atroi)liy of the gills. Moreover. the>e two i-henomena 

 liave nt'ver failed to occur in the metamorphosis of the 

 many hundreds of metamorphosin- larva^ ol)served in 

 the laboratory, and even in such lar\a' as wei-e forced 

 at a very early date into ))r.'c<.ci(ni- nu'tamorphosis by 

 the adndidsti-atioii of iod.itliyrim' and in which other 

 chan-es did not occur. .\nd furthermore, m>ither the first 

 moult n..r the reduction of the -ill. coidd ever l)e ob- 

 served in larva', whose met;imorpho>i> w;i> inhibited In- 

 dietary or other nu'ans. Thus I have coum" to look upon 

 the lirst moult and the atrophy of the -ills as two of the 

 ])rimai-y com|)onents of the salnmander uu'tnmoi'phoHs. 

 1 have not .'n<m-h i.ers.uial experience with the lnrv:e .•f 

 anurans. but feel encoura-ed throu,-li the experience,, 

 report.',] by other in V(-t i-ators to believe that in anurnns 



taiidy'the first shed.Hn- of the >kin >eems to accomp.any 



(38), and substances other than thyroid hormone or 

 iodine, such as the antei'ior lobe substance, altlH)u,-h they 

 may cause the limbs to grow, do m»t bring about atrophy 

 of the gills in tliyroidectomi/.ed tadpoles (L'7). 



It is <litrerent with the limbs, the pi.uiueulary pattern, 

 the tongue, the palatal teeth and the sex organ<: these 

 five groups of organs, at least in salamanders, have 



