Small pieces of bone from the caudal vertebræ were also transplanted, care being taken that each piece should contain some of the periosteum and marrow. The bone tissue goes to pieces, but the periosteum and marrow develop further. New bone is formed from the cells of the marrow as well as from those of the periosteum. Finally the entire piece, both its old and its new parts, is absorbed. Pieces of muscles were also absorbed. These experiments of Ribbert show that transplanted pieces of tissue do not increase in size by growth, but undergo changes which he describes as a return to an earlier condition of development. The abnormal condition of their existence seems to be the cause of this change. The transformation may be due to a change of nourishment, or to a loss of nerve influence, or to lessened functional activity. These results have a direct bearing on the problem of regeneration. They show that all kinds of tissue may continue to live, and the cells multiply in different parts of the body, but there seems to be nothing in these cases comparable to a regeneration of the entire organ. In the new situation the cells often assume an entirely new arrangement. After a period of activity, a process of degeneration commences, and the piece atrophies. Ribbert thinks that the atrophy is due to lack of nourishment, yet it is not clear how this could be the case, since for the first few weeks after transplantation there is an active growth, and in some cases, as in that of the bone, there is a formation of new, characteristic tissue. It may be that the transplanted tissues can no longer manufacture the substances necessary for their specific growth, and after the materials that have been brought along with them have been used up, the growth of the piece is stopped and its subsequent degeneration begins. It would be interesting to see if pieces transplanted to the same kind of organ as that to which they belong will become permanently incorporated in their new position.