Contributions to the Problem of Regeneration in Protozoa

Abstract

Regenerative capacity has been demonstrated in nearly all groups of free-living Protozoa, expecially in the Sarcodina and the Ciliata. Parasitic forms have been inadequately studied. The extent and course of regeneration in each instance are apparently limited by the pattern of normal reorganization attending asexual reproduction. It seems likely that there may be only one basic mechanism of reorganization, and that this acts in both normal and experimentally induced reconstitution. Within the Ciliata, there is a progressive specialization of regenerative response. Unlike the holotrichous forms (Paramecium, etc.). which exhibit replacement of missing structures in situ, hetero-trichs like Stentor possess well-marked anlagen of regenerating oral structures; these undergo initial differentiation and then migrate to their definitive positions. In the complex hypotrichs (Stylonychia, etc.). still more highly localized reorganization fields appear during regeneration; it is a remarkable fact that removal of even one ciliary organelle may cause a complete reorganization of all organelles in these forms. The observation by Calkins and others that. the regenerative capacity of "young" and "adult" individuals is different is extended by data showing physiological differences between these individuals. The actual mechanism underlying regeneration in Protozoa is still unclear. The nuclear apparatus (macronucleus of ciliates) undoubtedly plays an important role, but whether or not it elaborates formative substances that are distributed in the cytosome is still unproved.