Podwyssozki (’86) found that regeneration may take place in the kidney of certain mammals,--best in the rat, more slowly in the rabbit. The restoration of the lost part takes place first by replacement of the epithelium. The old canals may then push out into the connective tissue that accumulates in the new part, but there is no new formation of canals or of glomeruli. According to Podwyssozki the regeneration of the kidney is less complete than that of any other gland. Peipers has reinvestigated the subject, and his results agree in the main with those just given. He finds in addition that new canals may grow out from the old ones into the new part. Podwyssozki and Ribbert (’97) have found that the salivary gland has a remarkable power of regeneration. Ribbert removed a half (or even more than this) of the salivary gland of the rabbit. In the course of two or three weeks new material had developed over the cut-surface. In one case at least five-sixths of the gland had been taken out, and at the end of three weeks the gland had regenerated to its full size. Microscopic examination showed that the greater part of the gland was made up of new lobes, some of which were as large as, others smaller than, the normal lobes. The new part contained new tubes with terminal acini. These had arisen from the tubes of the old part. The connective tissue of the new part also came from that of the old. In this case a true process of regeneration takes place from the cut-surface; in addition a certain amount of enlargement, or hypertrophy, also takes place in the old part. Ribbert believes there is a connection between the process of hypertrophy and of regeneration of such a kind that the more active the one, the less active the other. Regenerative changes are known to occur in other internal organs besides these glandular ones. Broken bones are united, if brought in contact, by a process that involves a certain amount of regeneration. Although new bony tissue may be formed at the region of union, the bones of mammals and of birds do not seem able to complete themselves, if a part is removed, except to a limited extent. While the broken bones of the leg or of the arm have the power of reuniting if held for some time in place, yet in nature this condition can seldom be fulfilled, and the animal with a broken leg or wing will most probably be killed. Nevertheless, since the bones have this power at whatever level they may be broken (but only if they are kept together artificially), the process can scarcely have been acquired through the liability of the parts to injury. We find here another instance of a useful process existing in animals, but one that could not have been acquired by exposure of the part to injury. It is probable that this same property is found in all the bones of the body,--in those that may occasionally be injured, and in those that are not.