On the non-hormonal control of the termination of regeneration

Simultaneous amputation at three different anterior and three posterior levels in the earthworm Eisenia foetida did not produce any measurable effect on the number of segments regenerated posteriorly compared to controls with intact heads. In every group, the number of segments formed depended only on the level of the posterior cut, declining by ten every time the level of the posterior cut was moved ten segments further from the head end. Repeated anterior amputation to prevent regeneration of the brain and subpharyngeal ganglia was without effect. No consistent differences were observed in the anterior neurosecretory cells either at the start or the end of regeneration. These results are discussed in relation to the "progress zone theory," the limited clonal cell life theory, and the theory of "sequential cumulative inhibition." It is concluded that the information determining the number of segments regenerated posteriorly resides in the tissues adjacent to the cut surface.