Studies on Regulation. 



271 



place upon them. From each of these cut surfaces new tissue has 

 grown out at right angles and in much larger amount than on the 

 longitudinal cut surfaces just anterior to these. 



It should be noted that the position shown in Fig. 29 was never 

 taken by the specimen and has been used in the figure merely to 

 show the parts without overlapping. The position of the two 

 posterior ends usually approached that shown in Fig. 28, though 

 when the animal was holding tightly to the substratum the over- 

 lapping was much greater than in the figure. Most commonly 

 during ordinary creeping the tw^o regenerated "posterior" ends 



were apposed and turned dorsally so that neither of them touched 

 the substratum. The new tissue was not much used by the speci- 

 men for attachment to the substratum, the most posterior parts 

 of the lateral margins being employed instead. This functional 

 substitution of the lateral margin for the posterior end is in itself 

 interesting and determines certain other important features. The 

 parts of the lateral margins which formed the actual posterior end 

 of the piece reacted to contact with the substratum in much the 

 same manner as the posterior end in normal animals. If one of 

 the regenerated "tails" happened to be in contact with the sub- 

 stratum it often adhered to some extent. While the other tail 



