METAMORPHOSIS OF AMPHIBIAN ORGANS 277 



The two pieces however, did not act in this manner. On the 

 contrary : 



a. Pieces of skin grafted from one larva to another developed 

 the network and the yellow spots simultaneously with the host 

 instead of with each other; i.e., they developed the characteris- 

 tics of the adult skin only when the host developed them, and 



b. This resulted in the establishment of a more or less consid- 

 erable difference in the time of development of the adult charac- 

 teristics between the two pieces of skin taken from the same animal 

 provided such a difference existed between the two respective 

 hosts. This difference ranged from seven days to five months 

 with regard to network development, and from three days to 

 four months with regard to the development of the yellow spots 

 (separation of the network). 



Such a relation can exist only if at least one factor necessary 

 to the development of the adult characteristics of the skin is 

 not present in the skin itself but must be furnished to the skin 

 from the host. This factor which may be called "metamorphosis 

 factor of the skin" is a factor external to the skin, and metamor- 

 phosis is not a process of self differentiation, for it is dependent 

 on a body (host) which produces this factor. 



It appears therefore, that in the metamorphosis of the skin 

 a factor has manifested itself which is similar to the metamor- 

 phosis factor of the eyes and of the gills of Salamandra maculosa, 

 for the metamorphosis factor of all three organs is necessary to 

 induce metamorphosis in these organs and is primarily not con- 

 tained in the organs but in the body of the organism. From 

 experiments 33-34, of series XXV, it appears that the eye of 

 Amblystoma punctatum also follows this mode of metamorphosis. 



According to the method employed, the experiments described 

 in this paper could not be expected to furnish any evidence con- 

 cerning the question as to whether the second and third quality 

 of the metamorphosis factor of the eye of Salamandra maculosa 

 mentioned on the first page of this article, will be found again 

 in the metamorphosis factor of the skin of Amblystoma puncta- 

 tum, although this assumption seems justified. As to the fourth 

 characteristic of this factor, we have obtained a definite answer 



