Studies on Regulation. IV. 129 



In Figure 46 or through Its anterior portion. Within certain 

 hmlts the circular locomotion Is more marked as the obliquity of 

 the cut Increases, the reason being clear. If, however, the cut 

 be nearly longitudinal the slender strip on the longer side Is likely 

 to roll up and may act as a drag, thus complicating locomotion 

 and delaying or preventing typical regeneration. 



Figures 48-53 Illustrate the history of a piece cut in the manner 

 indicated in Figure 46 and moving In a curve toward the right. 

 Even as early as three days after section (Fig. 48) the new tissue 

 is symmetrical with respect to the cut surface, evidently In con- 

 sequence of the effect of locomotion. Figure 49 shows the con- 

 dition six days after section. Here the curvature of the new 

 tissue is becoming evident. In Figure 50 — tw^elve days after 

 section — the curvature of the regenerating part Is still more con- 

 spicuous. Twenty-eight days after section the tissue has acquired 

 the form shown In Figure 51. Now that the regenerated tissue 

 has attained a considerable length and its posterior region con- 

 stitutes the chief organ of attachment some degree of straight- 

 ening occurs. The manner in which this takes place is shown in 

 Figures 52 and 53, both of which represent the same stage — fifty- 

 eight days after section. Figure 52 shows the piece In ordinary 

 locomotion. Here the margins as well as the tip of the tail, or 

 frequently only the margins or certain regions of them, adhere to 

 some extent, and the resulting tensions cannot cause straightening 

 of the longitudinal axis since they follow approximately the same 

 curve. Frequently, however, only the posterior end of the body 

 adheres, or the margins of the head and the posterior end, and at 

 such times the piece assumes temporarily the form of Figure 53, 

 in which the axis is nearly straight. The longitudinal tension to 

 which the body Is subjected straightens it, but at the same time 

 bends the contracted posterior part of the old tissue to the left so 

 that the outline becomes convex at the left of this region. At the 

 same time small folds appear at x, indicating that In this region 

 the tissues are subjected to pressure instead of tension. This posi- 

 tion Is never maintained for any length of time, and as soon as 

 the tension ceases the piece resumes the form of Figure 52. There 

 can be no doubt, however, that if this position is taken sufficiently 



