THE LOCATION OF FACTORS OF HEAD REGENERATION IN THE EARTHWORM

¹ From the Biological Laboratories, Harvard University

1. The presence of pharynx at a wound region is not essential to head regeneration even though it may, under some circumstances, be the source of nerve material (brain).

2. While obviously not a head determiner, the intestine can participate in head regeneration apparently as readily as the pharynx can. Intestinal epithelium can redifferentiate into characteristic pharynx epithelium.

3. The presence of nerve cord at a cut surface is not an essential factor in head regeneration since a brain may develop independently of any cellular connection with the cord. There may, however, be some hormonal relation between the nerve cord and regeneration.

4. The nerve cord does not determine the type of there generate for:

(a) The anterior (cephalic) nerve cord can participate in heteromorphic tail formation as well as in head formation.

(b) The post-clitellar cord (within the first twenty-five segments behind the clitellum) can participate in head formation as well as in normal and heteromorphic tail formation.

5. The "sleeve" operation, consisting in grafting over the intestine, in normal orientation, segments of anterior body wall containing either no central nervous parts, or anterior or posterior nerve cord, was invariably followed by head regeneration except in most of those cases in which no nerve cord was initially present. The "sleeve" cases afford strong evidence that the epidermis of the anterior body wall, being the source of the brain anlage, contains the primary determiner of head regeneration, and that the seat of this determination is probably located in the dorsal part of the epidermis.