The Induction of Regeneration in the Hydroid Cordylophora Lacustris

Abstract

1. Beadle & Booth's work on grafting oral cones into reconstitution masses of Cordylophora lacustris has been repeated, confirmed and extended. Oral cone grafts induce the development from mass tissue of hydranth regions basal to the oral cone, and other regeneration of the mass is inhibited. Except in the most quickly developing material, induced development is significantly faster than 'spontaneous'development. 2. Inducing action when grafted to a mass is not peculiar to the oral cone but is a property of all tissue with hydranth differentiation (the tentacular ring, subtentacular region, hydranth neck and even pieces of tentacle), and of tissue containing the rudiment of hydranth differentiation (the tips of outgrowths developing from masses). Tissue which does not possess hydranth differentiation (unspecialized stem coenosarc and stolon tips) has no inducing activity but is absorbed into the mass without influencing its regeneration. 3. Grafts of basal hydranth regions and outgrowth tips normally regenerate oral cones out of graft tissue, but induction may occur even when no oral cone is regenerated by the graft. Tentacle grafts do not regenerate an oral cone; the oral cone of the induced hydranth develops from mass tissue. Inducing power therefore does not depend upon the regeneration by the graft of an oral cone. 4. Grafts of inverted oral cones or fragments of oral cones may produce induction. That inducing activity does not depend on the size, orientation or completeness of the grafted differentiated tissue further shows that it is the presence of hydranth differentiation in tissue, rather than any other factor, which confers inducing ability. 5. No induction has been produced when an oral cone graft is separated from the host tissue by an agar or a cigarette paper barrier. Direct close contact between the graft and the host appears to be necessary for induction to be produced. 6. Grafts of agar on to which oral cones have previously been squashed, macerated oral cones or killed oral cones do not produce induction. If macerated oral cone tissue becomes reorganized into a small fragment possessing the histological structure of part of an oral cone, induction may then occur. The separated constituents of differentiated tissue do not appear to be capable of producing induction.