Studies on Regulation. IV. 115 



of movement diverges less from a straight line than before, and 

 correspondingly the angle between the longitudinal axis of the head 

 and new body is decreasing. The new cephalic ganglion is nearly 

 as large as the old, but the eyes are still less numerous in the new 

 tissue than in the old. The regeneration of the lateral regions 

 of the head has proceeded so far that anterior to the eyes the new 

 portion is nearly as broad as the old. 



The change in form of the regenerating lateral margin of the 

 head is the most conspicuous feature of this stage (compare Figs. 

 16 and 17) . It has now acquired almost its typical form. More- 

 over, the curvature of the longitudinal boundary between the new 

 and old portions, /. e. the longitudinal cut surface, is decreasing. 

 Observation of the movements of this piece at this stage showed 

 that the functional activity of the regenerated margin of the head 

 was very great. It was much used in locomotion, portions being 

 extended anteriorly or antero-laterally, attached, and then con- 

 tracted, thus drawing the body forward. Swimming movements 

 were also often made, though short pieces of this kind do not suc- 

 ceed in swimming to any extent, being apparently unable to main- 

 tain their equilibrium in the absence of posterior parts of normal 

 size. There can be little doubt that the functional activity of 

 this region has brought about the change in form. Characteris- 

 tic movements have produced a characteristic arrangement of the 

 tissues. Moreover, the frequent extension of the margin anteri- 

 orly followed by attachment and contraction has undoubtedly 

 aided in forcing the anterior part of the old tissue toward the left 

 and thus straightening the outline of the cut surface. 



October 24: 54 days after section: 



As indicated in Figure 1 8 the changes described above con- 

 tinue. The piece moves still more nearly in a straight line than 

 twelve days ago and the form is correspondingly altered. The 

 present stage exhibits one interesting effect of the change in direc- 

 tion of the tension upon the tissues. During locomotion the 

 margin at a", including both new and old tissue, is thrown Into 

 small wrinkles or folds, while the right side of the body Is very 

 evidently stretched. The folds are clearly the result of the 

 altered direction of tension In the adjoining parts. The body 

 grew out in a direction differing considerably from that in which 



