Later stages of regeneration in the Polychaete, Nephtys.

Abstract

AbstractThe sequence of events in posterior regeneration of the polychaete, Nephtys, has been examined in histological preparations from the fifth day to the end of the third week after amputation, that is from the time when wound healing is complete until several new segments are differentiated. The pygidium forms and begins to differentiate prior to segmentation. The first indication of each new segment is the appearance of a large pair of segmental blood vessels which arise from the vascular complex in the gut wall. Associated with these are fibroblasts, the anlagen of the new septum. Epidermal derivatives develop subsequently, appearing first ventrolaterally, close to the regenerating nerve cord. The mitotic rate appears to be highest prior to the period of maximum segment formation. Visible cell differentation follows, and subsequent growth of segments is primarily by cell enlargement. It appears likely that the blood‐vascular system associated with the gut and the regenerating nerve cord, both of which are disproportionately large in the regenerate, are important for the initiation of new segments.