EDUARD UHLENHUTH 535 



such as the caecihans, legs are completely absent in the adult form 

 and yet a normal metamorphosis takes place in these amphibians. 



There are still other organs the development of which does not 

 seem to be caused by the iodine action in metamorphosis. It has 

 been observed by Cope^^ and confirmed later by Powers^" that in 

 Amhy stoma tigrinum under certain conditions metamorphosis may 

 take place without the tongue and the larval arch of the palatal teeth 

 developing the adult condition. From this may result metamorphosed 

 animals without tongue and with the larval arch of the palatal teeth 

 persisting. The substances causing metamorphosis apparently do 

 not influence the development of the two organs in question. Thus it 

 seems that at least six chemical mechanisms are present in the am- 

 phibian organism, one for metamorphosis, one for the skin coloration 

 of the adult, one for the sex organs, one for the legs, one for the 

 tongue, and one for the palatal teeth. The remarkable feature in the 

 amphibian development is that each of these mechanisms can act 

 independently without influencing the others; the organism as a whole, 

 as an organic individuality, seems to have no control over the har- 

 monic development of these groups of organs, since the chemical 

 mechanisms separately respond to conditions which are not located 

 within but without the organism. We will see now that one of these 

 conditions is the temperature, which affects the rate of some of 

 these mechanisms in a different way and consequently brings about 

 unequal development of various parts of the body. 



Influence of Temperature upon Metamorphosis and Coloration of 

 Amby stoma tigrinum. 



If the coloration of the skin is caused by substances different from 

 those which cause the amphibian metamorphosis, we can understand 

 the influence of temperature upon the coloration of Amhy stoma 

 tigrinum as observed in the following experiments. 



Two sets of larvce of Ambystoma tigrinum, Tigrinum 1917, Series S 

 and U, were kept at approximately 25° and 15°C. respectively; other- 



^^ Cope, E. D., The batrachia of North America, Washington, 1889, 73. {Bull. 

 U.S.Nat. Mus., No. 34). 



^^ Powers, J. H., Univ. Studies Univ. Nebraska, 1907, vii, 197. 



