The capacity of hydranths of Tubularia to regenerate or recoiistitute when cut during a process of reorganization already in progress has been the subject of many investigations and much controversy. The discussion has concerned both the fate of the distal fragment and of the stock of the primordium.
According to Bickford (1894), Driesch (1897) and Xorgan ( 'Ol), distal fragments show a certain amount of growth hut usually no regeneration of proximal structure, although Morgan asserted that it was possible, as did Peebles ( '00). Child ('07) also concluded that proximal structures were in general not replaced by more distal ones, and postulated the existence of a gradient in differentiation, the supposedly more highly differentiated distal regions being incapable of altering their reactions in thq direction of decreased differentiation. Proximal areas on the other hand were considered to be capable of increased specialization.
The greater part of the controversy has concerned the fate of the proximal p a r t remaining continuous with the stalk. The replacement of missing structures has been widely reported. Driesch (1897) described 4 methods by which replacements occurred : ' ' Regenerationsmodus," formation of new mouth and distal tentacles by a budding process of the emerging coenosarc ; "Ersatzanlagemodus," a new distal row of teiitacles forming anteriorly to the proximal before 4G.5