Studies on Regulation. IV. 1 1 1 



ceding and examined at the same Intervals. Figure 5 shows the 

 piece five days after section, Figure 6 ten days after section, and 

 Figure 7 twenty-seven days after section. In Figure 5 the new 

 tissue Is symmetrical with respect to the contracted cut surface 

 but not with the median plane of the animal. As growth proceeds 

 however, a gradual change In direction of the axis of the new 

 tissue occurs (Figure 6), until finally this corresponds with the 

 median plane and approximate bilateral symmetry of the whole 

 results, though the new tissue Is still unsymmetrical In form since 

 the surface from which It arose Is oblique. 



This change in the direction of regeneration Is also familiar 

 to students of regeneration, having been described by Morgan 

 and others for Planaria and other forms. It seems to bear the 

 stamp of a true regulative process for it brings the parts Into the 

 position which they must occupy In order to produce a bilaterally 

 symmetrical whole. 



During observations on Planaria in which the change Is well- 

 marked, the possibility suggested itself that it was primarily due, 

 not to some Internal factor operating In such manner as to pro- 

 duce the typical form of the species or an approximation to it, but 

 rather to the locomotion of the animal in the direction of the lon- 

 gitudinal axis. It appeared probable that since the new parts 

 were used for attachment and thus subjected to tension in the di- 

 rection of the longitudinal axis they were gradually drawn out In 

 this direction and so a symmetrical whole was produced. This 

 view was supported by the fact that the change seemed to begin 

 when the new part became functional. When the new tissue first 

 appears In these forms It Is apparently little used for attachment 

 or at least without complete success. Within a few days, how- 

 ever, the specimens can be seen to adhere closely to the substratum 

 by means of It, and it is at this time that the apparent change In 

 the direction of growth first becomes conspicuous. 



The question as to the effect of altering the direction of loco- 

 motion In pieces at once presented itself to me and fortunately I 

 found In Leptoplana a favorable form for experiments of this 

 kind. Short pieces from the body of Leptoplana containing the 

 cephalic gaoglia or a considerable portion of them move In circles 



