Experiments in Grafting 299 



different species of tadpoles to unite than pieces of the same 

 species, although Rana esculenta can be united with ease to 

 Rana fusca or to R. arvalis. The facility with which the pieces 

 unite is owing to the rapidity with which the ectoderm of Rana 

 esculenta covers exposed surfaces. Rana fusca and R. arvalis 

 do not combine so readily, because the ectoderm unites very 

 slowly. On the other hand, it is very easy to unite Rana escu- 

 lenta with Bufo igneus, but not permanently, as the parts die 

 or separate. In one case, however, the union lasted for three 

 weeks. Partial union, but of short duration, was effected be- 

 tween the tadpole of Rana esculenta and a larval Triton. 



Although some of these combinations between different 

 species lasted for some time, and seemed to be permanent in 

 several cases, each part developed only its own specific peculiari- 

 ties, as seen especially in the color. No hybridizing effects were 

 apparent. 



Harrison has united the anterior half of Rana virescens to the 

 posterior half of Rana paiustris, and has reared young frogs 

 from the combination. The anterior half of the body of these 

 frogs showed the characters of one species and the posterior part 

 that of the other. There was no trace of mutual influence 

 between the two halves. 



I have examined a case in which the relation of the parts is so 

 intimate that were there any influence exerted we should expect 

 to get evidence of it. The tip of the tail of a young tadpole of 

 Rana sylvatica was united to the tail of Rana paiustris (from 

 which previously an equivalent piece had been removed) (Fig. 

 22, B). As the new tail grows out, the dark ectoderm of R. 

 sylvatica is carried out to the tip (Fig. C), while the underlying 

 cells remain behind, and come to be covered over by the light 

 yellow ectoderm of R. paiustris. If now the tail is cut off at 

 the line indicated by the vertical line a-a, this cut end will be 

 made up of the inner organs of R. sylvatica, and, externally, of 

 the skin of R. paiustris. When the new tail regenerates (Fig. 

 E) the opportunity for mutual influence of the parts is afforded, 

 yet no such influence was apparent. Other experiments of a 



