REGENEEATION OF POLYCLADS 53 



In one series of experiments the anterior ends of worms were 

 split as nearly as possible along the midline. If the cut passed 

 slightly to one side of the brain, the edges of the womid closed 

 completely within three or four days, depending upon the length 

 of the cut. But if the brain was injured, in every case except two 

 the cut edges healed together up to about the level of the brain, 

 and from this point remained open indefinitely, the flaps thus 

 formed folding over each other. Examination afterwards show^ed 

 that the nervous tissue had been so injured that the contours of 

 the cephalic ganglia could not be recognized, and they were not 

 restored at the end of a month. In the two cases referred to, 

 portions of the cephalic ganglia remained. Eye spots and a 

 certain amount of anterior tissue were restored, though not in 

 sufficient amount to restore the normal form. There was no 

 addition to the amount of nervous tissue left in the pieces after 

 the operation. 



In one of the two cases the knife passed fairly exactly through 

 the center of the brain with so little damage to the nervous tissue 

 that each piece possessed practically half the brain. The left 

 side of the head with its two sets of eyes and tentacle on the 

 brain was separated from the rest of the body, and the regenera- 

 tion of both the smaller left piece and the larger right one were 

 followed for over a month. After six days regeneration became 

 evident in both pieces. On the tenth daj^ the smaller one showed 

 the characteristic tendency to accumulate material at the point 

 where the tail should appear, and about the fourteenth day the 

 digestive tract began to be evident in this projection. After 

 twenty-five dsiys eye spots showed the beginnings of a series of 

 right eyes, and the form of the worm was much like that of worms 

 sectioned transversely^ immediately behind the cephalic ganglia. 

 The final result a little over a month after the operation is shown 

 in figure 4. The larger piece began to show diverticula from the 

 digestive tract in the new material on the left side after twelve 

 days. Pigment spots also appeared at this time where the left 

 eyes should be. The form was never fully restored, since there 

 was not enough material to allow the worm to become straight 

 (fig. 5). When these two pieces were examined to determine 



