Experiments in Grafting 287 
correspond with that of the other. If, for instance, the nervous 
system of one piece is not opposite the nervous system of the 
other piece, regeneration at the place of union may subsequently 
occur. The nervous system is the most important factor in the 
result; for it acts as a center for the formation of the new part, 
which may be a head or a tail, or two heads, etc., according to the 
region that regenerates at the union. In some cases where the 
cut ends of the nervous system are not exactly opposite they find 
each other, and become united by a connective of nerve tissue, 
derived from the ectoderm of the region of union. The further 
the cut ends of'the nervous cord are apart, the less likely are they 
to unite, and regeneration from one or from both cut ends is 
more likely to take place. 
Born has shown that cut surfaces of very young tadpoles may 
be united, and he has made a great variety of combinations of 
these embryos. The method of grafting is very simple. The 
tadpoles are taken from the jelly capsules, cut in two with a 
sharp knife, and the cut ends quickly brought in contact with 
each other. The pieces are held in place by means of small 
blocks of silver." The combinations are permanent, and in no 
case does regeneration take place from the cut surface even 
when like organs are not united. The tail region of one animal 
has been united to various parts of the body of another animal, 
where it remains attached and continues to develop, producing 
its normal structures. In one case, the tail grafted upon the 
ventral surface of another individual showed signs of being 
absorbed at the time of metamorphosis, when the normal tail 
was absorbed. 
These results of grafting pieces upon parts of the body, differ- 
ent from those with which the part in question is continuous 
under normal conditions, show that the development of the part 
is due to self-differentiation, and that its development is not 
dependent on relation of the part to the rest of the organism. 
Parts of planarians have been grafted together by Mrs. Mor- 
1 T have found that bent pieces of aluminium wire and short straight pieces of 
the same wire cut off very obliquely can be used to hold the pieces together. 
