Abstract
The freshwater planarian Dugesia japonica was used to examine the influence on the axial polarity of a tail piece transplanted into the following three regions: in experiment I posterior to the head; in experiment II just anterior to the pharynx; and in experiment III in the postpharyngeal region. The hosts were transversely amputated at a level 0.5 mm posterior to the grafted site at various times after transplantation. After this procedure, the regenerating blastemas from the posterior cut ends of the hosts were examined to determine if they were the head or the tail. The regeneration of the head occurred as a result of the reversal of the original anteroposterior polarity of the planarian body.
In experiment I, when the hosts were amputated immediately after transplantation, a head regenerated in about 50% of the cases. The longer the time after amputation, the higher the rate of head regeneration, and the reversal of polarity was completed within 7 days or more after transplantation. In experiment II, the rate of head regeneration was lower than that in the first experiment at every time point after posterior amputation. In experiment III, a reversal of polarity was also observed, but the rate of head regeneration gradually decreased after the 4th day from the time of amputation, and the tail completed its regeneration on the 10th day in all cases. Based on these results, a discussion is presented on the role of the tail in axial polarity during its regeneration.