A Ringer fluid of 0.147M concentration is approximately isos-motic with the body fluids of Lumbriculus. In this and somewhat weaker solutions wound closure dif- fers from that occurring in fresh water. There is a protrusion and eversion of the gut and a partial failure to close the wound. In many cases no new tissue is apparent in individuals regenerating in approximately 0.14M solutions. Those pieces which do produce new tissue in 0.14M solutions do so only on the ventral side. The tendency to produce new tissues becomes greater the more hypotonic the solution. In Lumbriculus the dilution of the body fluids, by the passage of water through the open wound, is an important factor in arousing the cells to regenerative activity.