An Analysis of Mitotic Activity and the Question of a Thymus-Like System in Planarians

Publisher Website
Google Scholar
Abstract
In smeared fragments of Dugesia subtentaculata, mitoses were counted in the three parenchyma cell types acting in regenerative processes, i.e. cells of type I, residual plasms and syncytium. The mathematical analysis of results obtained with counts in regenerating or cultivated fragments clearly demonstrates that two distinct systems are involved in regeneration: syncytium and the system of cells of type I. Syncytium is the undifferentiated and totipotent material. Its mitotic activity lies near the transection surfaces and depends upon its localization. In in vitro cultures, the syncytium is more prolific when explants are formed by recently regenerated tissues. The system of cells of type I includes mother cells, cells of type I and residual plasms (cytolyzing cells of type I). This system is activated in the whole parenchyme after wounding or amputation but is not stimulated again when a second amputation is performed 8 days later (‘cinephylaxie’). The quantity of cells produced and then cytolyzed is independent of the quantity of lost tissues. The process looks like an inflammation. The system of cells of type I is similar to the thymus of vertebrates. It is characterized by the same overproduction of short-lived cells which cytolyze without pycnosis. It has the same sensitivity towards seasonal and nutritional factors; it increases its mitotic activity after injection of extraneous substances and exhibits the same phenomenon of cinephylaxie as the thymus.

This publication has 0 references indexed in Scilit: