26o C. M. Child. 



change in form of the new tissue from a rounded mass with convex 

 margins to the more elongated condition with concave margins 

 shown in Fig. 2. It is clearly evident that in this piece with short 

 posterior end the mechanical conditions connected with locomo- 

 tion are very different from those existing before section (Fig. i). 

 Before section this piece was continuous across the whole posterior 

 end with the parts posterior to it, and therefore any tension to 

 which it was subjected in consequence of attachment of the pos- 

 terior parts of the animal must have been approximately parallel 

 to the longitudinal axis. 



But after the regenerating posterior portion has begun to serve 

 as an organ of attachment (Fig. 2, two days after section) the lines 

 of tension are no longer nearly parallel to the longitudinal axis 

 but converge toward the posterior end (Fig. 2), this being the part 

 most frequently used for attachment. 



If the tissues of the body are at all plastic their relations must 

 be altered to a greater or less extent by these new conditions. The 

 effect of the tension must bring about elongation and decrease in 

 width of the body, most marked posteriorly and decreasing toward 

 the anterior end. And this is exactly what occurs. At the stage 

 of Fig. 2 attachment by the posterior end has been possible only a 

 short time and has not as yet affected any marked change in the 

 form of the piece. In Fig. 3 (twenty-seven days), however, the 

 form is greatly altered. Not only has reduction of size in the old 

 part occurred but its proportions are different (see table of 

 measurements). Its length is 25 per cent and its greatest width 

 33 per cent less than originally; moreover, it is now much narrower 

 at the posterior end than at the anterior end, whereas originally its 

 width was about the same at both ends. 



The Figs. 4-6 show later stages in the process. The change of 

 form is not great after the stage of Fig. 3, but in consequence of 

 the more rapid reduction in size of the old part as compared with 

 the new, some change does occur. It is of interest to note that 

 as the piece gradually becomes smaller and less active the length 

 of the old part decreases more rapidly than its width, 1. ^., it 

 becomes relatively wider (Figs. 4-6 and table). 1 his change is 

 always more or less evident in pieces of this kind and is exactly 

 the reverse of what might be expected if the change in form were 

 a "reduction to approximately normal proportions." Pieces of 

 this kind always show a decrease in motor activity after several 



