238 EDUARD UHLENHUTH 



I. INTRODUCTION 



In a series of experiments performed on larvae of Salamandra 

 maculosa in 1910, 1911 and 1912, 1 the writer studied certain 

 factors involved in the normal metamorphosis of the Amphibian 

 eye. It was shown that eyes taken from an old larva and grafted 

 to a young one, cannot metamorphose unless the host meta- 

 morphoses. The metamorphosis of the old eyes, therefore, was 

 delayed as compared with the time of metamorphosis of their 

 eye-mates left on the old larvae from which the grafted eyes were 

 taken. In one case in which the new host metamorphosed two 

 months later than the animal from which the grafted eye was 

 taken, the metamorphosis of the grafted eye also occurred 

 two months later than that of its eye-mate. Furthermore, it 

 appeared that the grafted eye must metamorphose at the time 

 that the eyes of the host metamorphose. When one eye of a 

 young larva was grafted to an old larva, the metamorphosis of 

 the young eye was accelerated just so much as to occur simul- 

 taneously with that of the host's eyes. In this way it was 

 possible to accelerate metamorphosis of the grafted eye by two 

 to six months. From these experiments, the following con- 

 clusion seemed justified; that metamorphosis of the eye is de- 

 pendent upon the presence of a particular factor without which 

 metamorphosis cannot occur, and that this factor cannot be 

 produced by the eye itself, but is developed in another part of 

 the animal's body whence it is furnished to the eye. 



When however, very old larvae such as were leaving the water 

 one or more days after the operation, were one of the two com- 

 ponents (host or graft) in these grafting experiments, the results 

 differed considerably from those described above. When one 

 of these very old larvae (called 'Larvenendstadium' in the first 

 publication) was the host the young grafted eye metamorphosed 

 at a later date than the host and furthermore, when such an old 

 eye was grafted on a young larva it metamorphosed long before 

 and independently from the host. Though in these 'Larven- 

 endstadien' the morphological change corresponding to meta- 



1 E. Uhlenhuth, 1913 a. 



