H^ MORGAN. [VOL. II. 



off the tails obliquely, as shown in the figure the more 

 anterior end on the dorsal side. Consequently, in order to 

 carry out the second operation of cutting off the tail through 

 the line of union, the cut was made also obliquely, but with 

 the ventral side forward. In a few cases the tails were first 

 cut off with the ventral side further forward (Fig. 2), and the 

 subsequent cutting off was made with the dorsal side forward, as 

 shown by a-a in Fig. 2, but the results were practically the same. 



It was found easier to graft the tail of Rana palustris on the 

 posterior end of Rana sylvatica than the reverse. On an aver- 

 age five operations of the former succeeded to one of the latter. 

 The reason for this cannot be given, but it may be due to some 

 difference in the relative sizes of the two components that is 

 more favorable for union in one than in the other way. The 

 result recalls the experiments in cross-fertilization of the eggs 

 in different species, where the crossing can be more easily 

 carried out in one direction than in the other. In this case 

 also the results may be due in some cases to a gross, physical 

 difference, as Pfluger has tried to show for the frog's egg. 



In the large majority of cases in which the experiment was 

 carried out as shown in Fig. I, the core of the new tail seemed 

 to be formed by the minor component, --i.e., if a yellow tail 

 (R. palustris) had been grafted upon a black tadpole (R. syl- 

 vatica) and then after twenty-four hours the tail had been cut 

 off obliquely (Fig. 4, A], the central part of the new tail would 

 be composed entirely of the yellow tissue derived from the minor 

 component (Fig. 4, B, C}. The small piece of yellow ecto- 

 derm is carried out on the new tail and remains near the tip. 

 It covers a larger area than at first, but it increases not nearly 

 so fast as the rest of the new, yellow tissue of the new tail. 

 The distinctive differences in color can only be seen in the 

 core of the tail, i.e., in the cells that form the muscles. On 

 each side of this axial core a broad fin is present containing 

 inside a gelatinous-like substance with scattered cells, but this 

 fin does not show any difference in color in the two species. 

 It is, therefore, probable that in many cases in which the core 

 of the new tail appears to be composed only of tissue from the 

 minor component that the ventral (or dorsal) connective tissue 



