70 H- W. Rand and E. A. Boyden, 



lated with the new head or independent of it. (See Fig. A, copied 

 from Voigt's paper.) If, however, the slip be one whose base re- 

 presents a more anterior and the tip a more posterior region of the 

 original tissue, then a new tail appears in the posterior part of the 

 new tissue on the mesial cut edge of the slip. Voigt's account leaves 

 it uncertain as to what species of worm was used in most of his 

 experiments. He considered his results chiefly in reference to the 

 question of heteromorphosis. 



Our object in repeating the experiments was to determine, so 

 far as possible, the factors which influence the development of these 

 lateral heads — particularly to investigate the relation of food 

 supply to the production of such structures which, so far as the 

 original individual is concerned, are certainly supernumerary and 

 useless. The attempt to carry out the experiments on Planaria 

 maculata met with unforeseen difficulties. Incisions were made 

 extending from the edge backward and inward, with a view to 

 securing lateral slips which should be attached posteriorly and free 

 at an anterior tip (Fig. B). If only a short oblique incision was 

 made, the cut edges reunited quickly and perfectly, and however 

 frequently, within practicable limits, the wound was reopened, no 

 projecting slip was produced. It was only by making a very long- 

 oblique cut, or one so deep that it extended nearly or quite to the 

 median plane of the worm, that the reunion of the cut edges could 

 be prevented by frequently reopening the wound. In a large pro- 

 portion of such cases the worm separated into two parts by trans- 

 verse fission at the region of the base of the lateral slip. In the 

 few cases where the process was carefully watched the separation 

 took place in such a way that the original tail was retained by the 

 lateral slip, while the piece carrying the original head was left 

 tailless. The separation commonly took place before the development 

 of new structures had progressed far. In some cases it appeared as 

 if the disruption of the individual resulted from the impediment to 

 locomotion afforded by the projecting part, which served as a drag" 

 upon the posterior portion of the worm. Consequently as the worm 

 advanced there was a state of tension at the region marked a & in 

 Fig. B, as shown b}^ the fact that this region became more or less 

 attenuated, and it was here that the separation was observed to 

 take place. 



So few successful results were secured from a large number oi 

 experiments that it soon became apparent that the original object 



