Several heterografting experiments between pieces ofHydra vulgarisandChlorohydra viridissimaand homografting ones ofHydra vulgarishave been made. The pieces have been obtained by means of a transverse cut at the body half. The heterografting had not joined, while the separated tissues of two pieces provided to recover and regenerate themselves. The fragments' gastrodermis maded a double cellular diaphragm, which crosses the coelenteron, parting it in two, parts each of one belongs to the higher piece and the other to the lower one. The homografting, on the contrary, remained permanently united, but sometimes the recovery of hydra has been accompanied by temporary growth of a gastrodermis sept crossing the coelenteron and which have then been reabsorbed. It seems thence that also in homografting there is a partial incompatibility of joining and a temporary tendency to regenerative autonomy between the higher and lower piece.