During the past 10 years considerable data have appeared indicatingthat the growth of hydroids is not, as was earlier believed,similar to the meristematic growth of plants, but rather thatthe sites of cell proliferation are removed in space from thesites of utilization, that cells migrate individually, activelyas amoebocytes through the epidermis or pawively as epitheliocytescarried along in the hydroplasm, to the sites of utilization,and that considerable migration across the mesoglea occurs. A model of hydroid morphogenesis and morphostasis based on thisnew information provides a comprehensive picture, albeit onefilled in with numerous assumptions, of the manner in whichcolony form is produced as a consequence of cell proclivities.