ii8 C. M. Child. 



was curved as shown in the figure. Only the piece on the right 

 of the cut will be considered here. After section the cut surfaces 

 contracted and the anterior end bent over so far that the outline 

 of the anterior region became almost symmetrical (see the outline 

 of the old tissue in Fig. 22). 



September 3 : 3 days after section : 



Figure 22 shows the piece as it appears at this stage. The 

 contraction has brought the two cut surfaces, originally at right 

 angles into almost the same plane. New tissue has begun to ap- 

 pear but there is no marked difference in amount in different re- 

 gions. That portion of the left cephalic ganglion which remained 

 in the piece protrudes slightly from the cut surface and is indicated 

 in the figure by deep shading. The piece moves in rather small 

 circles as indicated by the arrow. 



September 6: 6 days after section: 



As indicated in Figure 23 the new tissue, probably the ectoderm, 

 has united with the protruding portion of the left cephalic gan- 

 glion and is thus prevented from extending at this point. An- 

 terior and posterior to this region growth has occurred and in a 

 curious manner. It appears as if two posterior ends were forming, 

 one from the lateral region of the head, the other from the poster- 

 ior cut surface, both of them corresponding in direction to the ten- 

 sion resulting from locomotion. Both adhere to the surface to 

 some extent, but the posterior one somewhat more firmly. Several 

 factors combine to produce this peculiar condition : the piece has 

 contracted In such a manner that the cut surface from which the 

 left side of the head would normally regenerate faces somewhat 

 posteriorly; the union between the protruding nervous tissue and 

 the new tissue divides the growing region into two parts; and 

 finally the tissue representing the left side of the head is just be- 

 coming functional so that its margin reacts to the contact of the 

 substratum but does not yet extend anteriorly and contract strongly 

 and aid in locomotion, being instead stretched postero-laterally 

 since It adheres to the substratum until the forward movement 

 loosens It. This condition shows very clearly how effective me- 

 chanical tension may be as a ''formative factor." 



