METAMORPHOSIS OF AMPHIBTAN ORGANS 283 



It is to be regretted therefore, that there are no statements an 

 Weigl's paper as to when the individual used in the experiment 

 in question had hatched, nor is there any picture or measure- 

 ment of this individual to be found indicating the appearance 

 of the individuals which Weigl 7 calls 'young.' Furthermore, 

 although it is true that the photograph leaves no doubt as to 

 the fact that the host was still a larva, there is unfortunately, 

 in this photograph no definite indication that the graft had 

 actually metamorphosed. It seems to us that the records ac- 

 companying the paper are not as complete as they should be to 

 lead us to accept this remarkable and only exception among so 

 many experiments. 



Fourth: to a young larva of Salamandra maculosa a piece 

 of skin from a young larva of the Mexican axolotl was grafted; 

 a short time after the host had metamorphosed the skin graft 

 metamorphosed also. It is well known that the variety of the 

 Mexican axolotl bred in Europe, does not metamorphose and in 

 the case before us the axolotl larvae which were kept as control 

 did not metamorphose even after they were removed from the 

 water and set on land. They did not show the slightest indi- 

 cations of metamorphosis when the grafted piece of skin meta- 

 morphosed. Weigl himself cannot but admit that the graft 

 in this case was forced 'into metamorphosis by the host — even of 

 a foreign species. In the face of this experiment, which is in 

 accordance with the experiments reported by the writer in this 

 article and in a former paper, and which supports the viewpoint 

 held by the writer, it seems difficult to understand how Weigl 

 could defend the idea that metamorphosis of the skin is a process 

 of self differentiation. 



If we compare the results mentioned in the foregoing four 

 paragraphs we shall appreciate how much they would lack in 

 uniformity if viewed from the standpoint that metamorphosis 

 is a process of self differentiation; i.e., that all factors necessary 

 to the metamorphosis of an organ are contained and developed 

 by this organ. It seems, however, that all results, including 

 those obtained by Weigl so far as they are based on definite 



7 .R. Weigl, 1913, figure 7, plate XXVIII. 



