The Role of the Nervous System in the Planarian Regeneration II. Regeneration of the Body Fragments with the Reversed Nerve Cord

In order to determine the influence of the nerve cord on the polarity of the blastema regeneration in Dugesia japonica, three groups of isolated body fragments with the reversed ventral nerve cord were prepared; 1) fragments with one nerve cord intact and the other rotated; 2) fragments with only one nerve cord reversed; 3) fragments with three nerve cords which consist of two intact nerve cords and one reversed nerve cord transplanted between them. Although the experimental fragments developed into regenerates of various shapes, the results in al the experimental series agreed in that a head is regenerated from the posterior cut end of the fragments with the original anterior end of the rotated nerve cord. From these results, we discussed the role of the biological polarity of the nerve cord in determining the differentiation of the regenerating blastema.