278 EDTJAKD UHLENHUTH 



in the experiments of series XXVI on heteroplastic transplanta- 

 tion. Pieces of skin and eyes of A. punctatum when grafted to 

 another species (A. tigrinum), showed exactly the same mode of 

 metamorphosis as they showed when grafted to an individual 

 of their own species. Metamorphosis of these two organs did 

 not take place unless and until the host metamorphosed. After 

 we have seen that neither of these two organs contain the meta- 

 morphosis factor, this can only mean that the factor has been 

 furnished to them from the body of an individual of a foreign 

 species. Hence the factor in question must be 'non-specific.' It 

 was mentioned on page 239, that some evidence of non-specificity 

 was also found for the metamorphosis factor of the eye of 

 Salamandra maculasa. 5 



2. One objection might be raised against the method employed 

 here. In certain cases of skin grafting the grafted pieces of skin 

 are soon partly or entirely replaced by the host. 



If, then, in the experiments of series XXV the skin graft 

 had been replaced by the skin of the host before the appearance 

 of the network or the yellow spots, the yellow spots developed 

 on the place corresponding to the grafted piece of skin, would 

 actually have been spots of the host and not of the graft. It 

 would not be surprising then that these spots always developed 

 at exactly the time that the rest of the spots of the host developed. 



Although the fate of the grafted skin of the homoplastic series 

 has not been followed on histological sections, there is enough 

 definite evidence at hand to show that no replacement of the 

 graft took place. 



First: the edges of the graft retain complete definiteness 

 throughout the larval period. This can be ascertained as the 

 color of the graft and that of the host show as a rule at least 

 slight individual differences (fig. 13). Later on when the animals 

 are entirely metamorphosed, graft and host are uniformly black 

 and the borders of the graft can no longer be distinguished. This 

 'fact does not interfere with our results, however, as at this 

 time the phenomena on which the present investigation is based 

 are long past. 



6 E. Uhlenhuth, 1913 c, p. 353. » 



