Inequality of the two Eyes in reg'enerating Planarians. 75 



line indicates the general position of the second cut. In Fig. F is 

 shown the form which the worm takes almost immediately after the 

 second cut is made. The contraction which always takes place in 

 the region of a cut has caused the worm to become concave in out- 

 line along the side from which the longitudinal strip was removed. 

 The curving of the axis following the second cut is in direction the 

 reverse of that caused by the first cut. The change of curvature 

 does not extend in any marked degree into the immediate region 

 of the regenerated eyes, nor does it noticeably alter the configuration 

 of the regenerated tissues. The direct effect of the second cut, so 

 far as change of form of the remaining material is concerned, is 

 confined mostly to those parts of the worm lying directly mesiad 

 of the newly cut edge. After the second cut the conspicuous cur- 

 vature of the worm is the convexity of its axis toward the side 

 opposite the newly cut edge. The opposite curvature resulting from 

 the first cut persists in the anterior portion of the worm, but it is 

 less conspicuous than the newly acquired curvature. 



The direction of locomotion of the worm is affected by the cur- 

 vature of the axis. After the first cut the worm tends, in general, 

 to progress in curved lines whose convexity corresponds in direction 

 to the convexity of the anterior portion of the worm's axis. The 

 larger eye is therefore in most cases on the convex side of the curve of 

 locomotion. After the second cut the worm tends to move in curves 

 whose convexity corresponds in direction to the convexity of axis 

 produced by the second cut. (The arrows in Fig. E and F indicate 

 the direction of locomotion.) The curvature of the line of locomotion 

 is therefore reversed from one side to the other. Accordingly the 

 eye - — usually the larger one — which before the second cut was 

 on the outside of the curve of locomotion comes to be, after the 

 second cut, on the inside of the curve of locomotion. 



Now, of the three worms above referred to upon which this 

 second operation was carried out, two just before the second opera- 

 tion had the outside eye larger (as represented in Fig. E) and the 

 third had the inside eye larger. None of the eyes were fully deve- 

 loped. In the course of some three days after the second operation 

 it was found that, in the two worms which before the second opera- 

 tion had the larger eye outside, the relative sizes of the two eyes 

 had been reversed. The second cut must have caused a change 

 in the rate of growth of the eyes such that the eye which had 

 formerly been the smaller gained upon and eventually exceeded the 



