1. The change in the form of a laceration piece, leading up to the acquisition of the typical actinian shape, takes place through the upgrowth of the tissue about the orifice where it was torn off from the parent. 2. The permanent mesenteries arise as new growths in the undifferentiated tissues of the oral end of the laceration piece. 3. The first twelve mesenteries do not appear in the sequence followed by those in egg embryos. 4. As development goes on the old mesenteries—those brought over from the parent when the fragment was torn off—become restricted to a proportionately shorter and shorter part of the base of the young actinian until they are finally entirely resorbed. 5. The mesenteric filaments are formed, just as in egg embryos, from a downgrowth of the ectodermal lining of the stomodeum. Their trilobed condition arises through the differentiation of this tissue. 6. The tissues of the most actively growing part of a laceration piece become very thin; the ectoderm and the entoderm lose all apparent cell boundaries; the mesoglea arises as a direct continuation of that present in the older tissues. 7. The newly formed tissues contain a very small number of gland cells and nematocysts. These two types of cells are developed to the usual number after the tissue relations have become stable.