Metamorphosis of Skin in Amphibians. 91 



it can also be furnished to the skin by the body of another species. 

 Fig. 7 shows a specimen of A. tigrinum, to which a piece of 

 skin with the eye from a larva of A. punctatum was grafted. In 

 four other specimens of A. tigrinum which had a similar graft, 

 metamorphosis had occurred from 1 to 6 weeks ago; in these 

 animals also the graft was metamorphosed. The animal shown 

 here was still larval, when painted, as you see from its color and 

 large gills. The graft, as you see, is also larval. The skin is 

 even grayish brown and the eye shows the ring still. It was not 

 until after about three weeks that this animal also metamorphosed 

 and then, simultaneously with its host, also the graft metamor- 

 phosed. The animal was painted again on November 24, the 

 ring of the eye is gone and only a few yellow spots, instead of the 

 ring are left (Fig. 8). 



Hence what these experiments show is that under normal 

 conditions a certain agent induces metamorphosis in the Amphib- 

 ian organs; that this agent cannot be produced by the organs 

 themselves, but must be furnished by the animal's body; that 

 metamorphosis can be delayed as long as the agent does not 

 reach the organs and that this agent is a non-specific one, as it 

 also is produced by another species. 



According to the method of these experiments it was only 

 possible to delay metamorphosis (by seven months in the case of 

 the eye experiments on Salamander maculosa). I am, however, 

 fully aware that it will be necessary to show that metamorphosis 

 can be entirely prevented if the agent is permanently kept away 

 from the organs, as only this will demonstrate that it is actually 

 a substance produced outside the organs — a substance which in 

 no way can be produced by the organ itself. Such experiments 

 have been started several times but could not be finished, as it is 

 very difficult to obtain the proper material and to obtain it just 

 at times when it is needed. 



