272 EDUARD UHLENHUTH 



organs of A. tigrinum are entirely different from those of the 

 graft. Consequently only one definite step was left to which 

 to refer the changes of the grafted punctatum organs, and that 

 was the moment when the tigrinum host leaves the water. Doubt- 

 lessly, a certain amount of inaccuracy enters these experiments, 

 for different individuals may show a different degree of develop- 

 ment of some of their characteristics when they leave the water, 

 a condition frequently noted during observation of a large 

 number of Urodelan larvae. We shall see, however, that the 

 difference in the dates when the hosts left the water is wide 

 enough to establish a corresponding difference between the 

 grafts and to make the relation between host and graft a definite 

 one. 



Furthermore, it must be said that it was not known exactly 

 when the grafts would have metamorphosed if they had remained 

 with individual A., for this individual had been killed and could 

 not be used as a standard. But an approximate normal stand- 

 ard-time of the metamorphosis of the graft can be calculate4 

 from the records made about the time of metamorphosis of the 

 entire stock of A. punctatUm larvae from which our grafts were 

 taken. According to these notes, from approximately 300 

 punctatum larvae all but about 10 metamorphosed before October 

 1, 1916. Four of the five grafts to be reported also metamor- 

 phosed before this time, together with their hosts ; the fifth meta- 

 morphosed late in October and later than any A. punctatum 

 larva of the entire series of experiments described in this paper. 

 As the respective host showed a corresponding difference, com- 

 pared with the other hosts, it seems justified to conclude that 

 in all probability the time of metamorphosis of the grafts in this 

 series (XXVI) was also determined by the hosts. 



The material used as grafts was the same as used in Series 

 XXV ; all animals were hatched on May 6 and were in this case, 

 the offsprings of the same mother. The tigrinum larvae were 

 collected in the early part of July, 1916 in ponds on Long Island 

 by Mr. Deckert and myself. 



The operations were performed on July 21 at which time the 

 tigrinum larvae ranged from 57.00 mm. to 87.50 mm. and still 



