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 palustris, 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 palustris (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. palustris. 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. palustris. 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 
