72 



H. W. Rand and E. A. Boyden. 



in Fig. D. A head is now distinctly formed in the new tissue at 

 the anterior region of the cut edge, where growth appears to have 

 been most rapid. 



A noteworthj^ feature of the new head is the inequality in the 

 size of the two eyes. The outer eye (that is, the eye nearer the 

 convex side of the slip) is well formed. It shows the characteristic 

 pigmented cup situated in the midst of a well defined clear region. 

 The other eye, however, is still at an early stage of development. 

 The clear region surrounding it is well defined, but only a minute 

 speck of pigment marks the position of the optic cup. Accurate 

 measurements of the organs in the actively moving worms was not 

 possible, but it is safe to say that the greatest dimension of the 



a^ b 



Fig. A. After Voigt. Fig. B. 



Fig:, c. 



Fig. D. 



pigmented mass in the left eye was about three times the diameter 

 of the pigment spot representing the right eye. During the next 

 few days the inequality of the two eyes diminished and the right 

 eye gradually became like the left. On the thirteenth day after 

 cutting, the greatest dimensions of the left and right pigment masses 

 were about in the proportion of three to two. At the end of the 

 third week both eyes appeared to be fully developed, perfectly 

 normal, and exactly alike in size. Meanwhile the new head had 

 assumed normal proportions and the curvature of the lateral slip 

 had greatly diminished. 



In every one of the six regenerating lateral slips the two eyes 

 were of unequal size during the earlier stages of their development. 

 The degree of inequality varied considerably. In one case markedly 

 more pigment appeared in one optic region than in the other and 



