METAMORPHOSIS OF AMPHIBIAN ORGANS 265 



to that of experiment 13 and 45. The network of the host did 

 not separate when the network of the graft loosened up into spots, 

 but needed five days longer for this process and even then had 

 not entirely disappeared. When the animal had completed 

 metamorphosis it turned out to be again one of those individuals 

 whose skin is almost lacking in yellow pigment; only a few light 

 spots had formed on each shoulder (fig. 10). This case will be 

 discussed together with experiments 13 and 45 later on. 



In experiments 11-12 we have a case similar to experiment 28 

 which will demonstrate particularly well the difference between 

 the factor that is concerned in this kind of delayed development 

 of the yellow spots and the factor which is involved in metamor- 

 phosis, for in this case both hosts were of this almost spotless 

 variety and both behaved towards the grafts in a similar way. 

 In addition to this, the grafts were taken from an animal whose 

 spots were characterized by a particularly vivid and almost 

 orange yellow coloration as shown by the fact that both grafts 

 showed this feature in the same way. Since both characteristics 

 are permanent even after metamorphosis (figs. 11 and 12) they 

 apparently must be parts of the specific individuality of the adult 

 animal, which of course, cannot be changed by the action of the 

 metamorphosis factor, but on the contrary should be developed 

 by this factor. 



In the experiments mentioned until now the difference be- 

 tween the rate of development of the two grafts was rather 

 slight, ranging from seven to twenty-eight days in regard to the 

 network and from three to twenty-three days in regard to the 

 spots. This was apparently due to the fact that the respective 

 hosts did not show any greater differences. The last pair of 

 experiments, however, will prove that the difference between 

 the rate of the grafts increases in exactly the same way as the 

 difference between the rate of development of the respective 

 hosts increases and that one graft may metamorphose very 

 much earlier than the other one as soon as one succeeds in ac- 

 celerating metamorphosis of one of the hosts and in delaying 

 metamorphosis of the other host a considerable length of time. 



