Inequality of the two Eyes in regenerating Planarians. 77 



Following this negative outcome of the second cutting, these 

 worms were subjected to a third operation, performed on the seven- 

 teenth day after the original decapitation, consisting in removing 

 the regenerated head by cutting as closely as possible along the 

 line between old and new tissue — a repetition of the first opera- 

 tion. But the conditions after this third operation were unlike those 

 after the first operation owing to the intervening second cut. For 

 the curvature caused by the long lateral second cut still dominated 

 the greater part of the worm, and the reverse curvature caused by 

 the closing and healing of the third cut aifected only a relatively 

 small anterior portion of the worm, that portion having already 

 been curved in similar manner by the first cut. After this third 

 cutting, therefore, the conditions which it had been sought to pro- 

 duce by the second cut were practically regained, with the diiference 

 that the main curvature of the axis, due to the second cut, was 

 established in advance of the oblique decapitation of the worm, 

 instead of after it. Thus whatever effect, if any, the long lateral 

 cut might have upon the regeneration of the eyes would be opera- 

 tive from the beginning of their regeneration instead of being inter- 

 jected into the midst of the process. After this third cutting obser- 

 vations were completed upon only nine of the seventeen worms. 

 Six days after the third cutting six of the nine worms had unequal 

 eyes and the larger eye was outside with reference to the main 

 curvature of the axis, that is, the curvature resulting from the 

 second cut (see Fig. G). Thus the larger eye in these six cases was 

 on the side where, if oblique decapitation had been the only opera- 

 tion performed upon the worm, the smaller eye was to be expected. 

 In one case of the nine the eye upon the inside of the main curva- 

 ture of the axis — the side from which the long strip had been 

 cut away — was the larger. In another case the two eyes were 

 equal, and in the ninth case a single median eye was developed. 

 Altho the number of individuals dealt with in this series of experi- 

 ments was small, the distribution of the results suggests very 

 strongly that the regeneration which followed oblique decapitation 

 was in some way influenced by the removal of a long strip from 

 one lateral edge. 



IV. A variation of the experiment consisted in decapitating and 

 removing a lateral strip as nearly as possible at the same time. In 

 five cases this was done, the decapitating cut being oblique to the 



