ABSTRACT
Evidence has been obtained showing that unlike the requirements of errant polychaetes studied by other investigators, at least two species of sedentary polychaetes, Branchiomma nigromaculata and Chaetopterus variopedatus can undergo caudal regeneration in the absence of a brain.
Both Branchiomma, when maintained in a brainless condition by repeated removal of anterior segments, and Chaetopterus, when rendered brainless by amputation of cephalic segments at a level at which anterior regeneration does not occur, undergo posterior regeneration following removal of caudal segments.
Animals maintained in a brainless condition for 7–10 days prior to posterior segment removal undergo normal posterior regeneration. Consequently, it appears unlikely that a circulating brain hormone present at the time of amputation is responsible.
Experiments were performed on the extremely long 13th segment of Chaetopterus. An isolated posterior half of segment 13, which possesses ventral ganglia, regenerates both anteriorly and posteriorly, while the anterior half regenerates only anteriorly. That the tissues of the anterior half of segment 13 are competent to regenerate posteriorly was shown by leaving the anterior half of the segment attached to the first 12 segments. Under these conditions posterior regeneration occurred.
These experiments suggest that the ventral ganglia rather than the brain are important in posterior regeneration in these species.
