The grafting-experiments that have been described in the preceding pages were carried out with pieces of adult organisms. Somewhat different conditions are present when parts of the developing egg or embryo are united, inasmuch as a process has been started in them that may go on independently, to a certain extent, of the union of the pieces. Born has carried out a large number of experiments in grafting parts of tadpoles of the same species, and also of different species. The union is brought about at the time when the tadpoles are about to leave the jelly membranes. The cut-surfaces are brought in contact and the pieces pushed together and held in place for an hour or two by means of small silver blocks or pieces of wire. The pieces readily stick together, and the union is a permanent one. Before describing Born’s results, it may be well to consider the power of regeneration of young tadpoles. If the tail is cut off a new one is regenerated by the tadpole, but all parts of the body do not have this same power. Schaper found that if a part of the brain, or even the entire brain, is removed, no regeneration takes place. I have found that if the region where the heart is about to develop is cut out from a young embryo, a new heart is not formed.[87] If a tadpole is cut in two across the middle of the body, neither piece regenerates the missing half. Byrnes has found, however, that if the region from which the posterior limb develops is cut out a new limb regenerates. In older tadpoles, Spallanzani found that if the hind limb is cut off it will regenerate, and Barfurth has more recently confirmed this result. The end of the tail that has been cut off from a young tadpole, before the tail has begun to differentiate, may continue alive for several days. It grows larger and flatter, and the V-shaped mesoblastic somites are formed. A slight regeneration even starts at its anterior end, as first observed by Vulpian and later by Born. The notochord and nerve-cord may send new tissue into the new part, and even some of the muscle cells may extend into this part, but the piece dies before regeneration goes any further. If, however, the tail is grafted in a reverse direction on the body of another tadpole, the regeneration may go further and produce a _tail-like_ structure, as Harrison discovered and as I have also seen.