METAMORPHOSIS OF AMPHIBIAN ORGANS 239 



morphosis was not developed at the time of operation, the factor 

 necessary to its production was apparently already contained 

 in the eye. The young eyes grafted to the old animals on the 

 other hand, did not metamorphose simultaneously with the 

 host, because one or two days of action of this factor is ap- 

 parently not sufficient to produce metamorphosis. 



Thus, in the case of the eye of Salamandra maculasa the ex- 

 istence of a definite factor involved in the metamorphosis was 

 shown. It was found (1) that this factor cannot be produced 

 by the eye itself but originates in the body of the host, the 

 exact part being unknown; (2) that it must act a certain length 

 of time in order to start the process of metamorphosis and (3) 

 that metamorphosis will occur if once induced by this factor, 

 even if the organ is removed from the further influence of the 

 action of the factor. 



The fourth characteristic of the metamorphosis factor could 

 not be precisely determined as the number of experiments was 

 not sufficiently large. It was observed that eyes of salamander 

 larvae also metamorphosed when grafted to larvae of Triton. 

 These experiments suggested that the metamorphosis factor is a 

 non-specific agent, but owing to the small number of experi- 

 ments no comment was made at that time. 



The first three characteristics however, were observed with 

 such regularity that they were considered to be definite rules 

 of the process of metamorphosis and apt to throw some important 

 light on this phenomenon. In order to justify this opinion it was 

 considered particularly necessary to examine several of these 

 organs, the metamorphosis of which is most prominent and to 

 find out whether the metamorphosis of these organs is subjected 

 to similar or identical rules as the metamorphosis of the eye. 

 If this were so, one would be justified in thinking that one 

 single factor governs the metamorphosis of all these organs and 

 that a common center in the body responsible for the develop- 

 ment of this metamorphosis factor could be found. 



It was from this idea that Kornf eld's experiments on the 

 metamorphosis of the gills originated. By grafting the gills 

 in a similar way as the eyes, it was proved that also in the meta- 



