Studies on Regulation. IV. 119 



September 10: 10 days after section: 



Unfortunately the condition described above did not continue, 

 for the ganglionic mass became separated from the right ganglion 

 and remained united with the new tissue on its dorsal surface near 

 the left margin (Fig. 24). In consequence of this change the 

 regions of new tissue before separated are now continuous and the 

 outline of the margin is rapidly undergoing alteration. More- 

 over, the new lateral tissue is now further developed functionally 

 and its margin reaches forward, attaches itself and contracts in 

 the characteristic manner, this assisting in the locomotion which 

 consequently becomes slightly less curved in direction. Corres- 

 ponding with this increase in characteristic functional activity is 

 the convex outline of the lateral margin of this region. As long 

 as it was being subjected to postero-lateral tension this portion of 

 the margin was in part slightly concave like the sides of a growing 

 tail or body ( Fig. 23 ) . 



The mass of ganglionic substance affords a landmark which 

 enables us to determine that the terminal portions of the body are 

 formed first, a conclusion agreeing with that of various authors 

 in regard to soft parts at least in other forms. 



September 20: 20 days after section: 



Figure 25 represents the condition at this stage. The direction 

 of movement is still far from a straight line, though the curvature 

 is decreasing. The curved body and pharynx require no special 

 comment. The new lateral region of the head now functions 

 very activ-ely and a comparison of Figures 23, 24 and 25 shows 

 that the curve of contraction of the original cut surface is becom- 

 ing less marked, i. e. the old tissue is being pressed back toward 

 the right at the anterior end by the active new tissue. Regenera- 

 tion of the left cephalic ganglion is taking place. 



October 12: 42 days after section: 



The new lateral region of the head is now so active that it 

 counterbalances the old part to a considerable extent and the di- 

 rection of movement is less curved. Figure 26 shows the speci- 

 men at this stage. The change in form and the growth anteriorly 

 of the lateral region is marked (compare Figures 25 and 26). 

 Small folds at x during locomotion indicating the pressure exerted 



