ABSTRACT
The regeneration of the planarian Dendrocoelum lacteum has been tested at three different levels of amputation : just behind the eyes, half-way between the eyes and the pharynx, and just in front of the pharyngeal base. The plana-rians always regenerate in the first case, never in the last case, and about 7 times out of 10 in the intermediate case.
Experiments involving amputations and irradiations show that there are regeneration cells (neoblasts) in the regions behind the pharyngeal base, regions which are unable to regenerate.
When they are not irradiated, these neoblasts are able to move towards the head and to restore the irradiated regions. They reconstitute a blastema with eyes, the number of cases directly depending on the prepharyngeal level of the section.
The histology confirms the experimental results and demonstrates the processes of regression, of necrosis, and then of colonization of the irradiated regions.
