Inequality of the two Ej'es in regenerating Planarians. 71 



of the experiments must be abandoned, in view of. the fact that the 

 work was necessarily being done within narrow time limits. However, 

 in the few cases where the lateral slip remained attached to the 

 head-bearing- portion of the worm long- enough for new structures to 

 become well formed, a striking peculiarity was noted in the develop- 

 ment of the eyes belonging to the new head on the lateral slip. This 

 peculiarity was made the subject of some further study with which 

 this paper has to deal. 



Experiments. 



I. Thirty-flve worms were cut in the way above described 

 with a view to producing projecting lateral slips with free anterior 

 ends. In all but six of the thirtj^-five cases there was either com- 

 plete reunion of the tissues along the cut edges, in spite of frequent 

 reopening, or else separation of the slip and the main portion of 

 the worm occurred before regeneration had progressed far. In the 

 six cases where a new head developed on the slip while it was 

 still attached to the main part "of the worm, the oblique cut was 

 long and deep — about half the length of the worm and ex- 

 tending nearly to the median plane. The behavior in all six cases 

 was essentially alike. 



Immediately after the cutting the main portion of the worm 

 became bent so that its axis was concave on the side toward the 

 cut. The lateral slip became even more decidedly curved, and so 

 that the cut edge was on its concave side. This curving of the 

 two portions of the worm caused them to interfere with each other, 

 as a result of which the free end of the slip was sometimes thrust 

 over or underneath the larger part of the worm. In the course of 

 a few days after the operation the slip, still sharply curved toward 

 its cut side, came to project at a considerable angle to the original 

 axis of the worm, so that collision of the two parts was then 

 largely or entirely avoided (see Fig, C). During the first week after 

 cutting, new tissue developed along the cut edge of the slip. This 

 new material appeared in much greater mass at the anterior region 

 of the cut edge than elsewhere. Numerous other observers of 

 planarian regeneration have noted that, in regeneration at an oblique 

 anterior cut surface, the new material accumulates .most rapidly at the 

 anterior region of the cut edge. Fig. C shows the condition of 

 a typical one of our six cases about five days after cutting. The 

 same worm, on the tenth day after cutting, appeared as represented 



