INCOMPLETE REGENERATION IN LEPTOPLANA LITTORALIS 1 9! 



about two or three weeks, often in two symmetrical groups, 

 but sometimes with irregularities in size and position. The pieces 

 at first were sluggish, and behaved like piecesi from which the 

 whole anterior end including the ganglia hai been cut off, but as 

 the eye-spots and other missing parfs appeared the worms be- 

 haved more like the normal animal. In the light of what fol- 

 lows, it would be interesting to make more detailed observations 

 on this point, for, in spite-of the external signs of complete regen- 

 eration, sections show that the ganglia themselves have not re- 

 generated. In the normal worm, the cephalic ganglia are well 

 defined, and enclosed in a distinct sheath, and have the appear- 

 ance in section of a brain of two hemispheres. The large nerve 

 cords pass through the sheath and are connected with the gan- 

 glion (Fig. B, i). In the regenerated worms, in place of the 

 definitely defined cephalic ganglia, nerve fibers alone are present, 



FIG. B (i), Diagrammatic figure of the cephalic ganglia, nerves and eye-spots of 

 a normal worm, taken from a horizontal section. (2), Diagrammatic figure of the 

 nerves in the position of the ganglia, in the regenerated worm of Fig. A (2), seven 

 weeks after the removal of the cephalic ganglia. 



which connect the large anterior and posterior nerve cords of the 

 two sides of the body (Fig. B, 2). The eye-spots of the normal 

 worm are more numerous and cover a larger area than in the 

 regenerated worm. In the latter, the eye-spots are usually 

 found in two well defined groups, though sometimes, crowded 

 out of place or irregular, when the wound has healed in such a 

 way as to leave too small a space for them to develop in the nor- 

 mal position. 



In the absence of the ganglia it seems to be a fact that the 

 presence of some anterior tissue is conducive to regeneration. It 



