Studies on Regulation. 



263 



In general the change in proportions in this piece was less 

 marked than in other similar pieces. The relative decrease in 

 width at the posterior end of the old part was less than usual. 

 Possibly the tissues of this individual were less plastic than in 

 most cases, but I think it more probable that an individual pecu- 

 liarity in the activity of parts of the margin during locomotion is 



responsible. Throughout the course of the experiment it was 

 noted that the small protruding part on the left side was very 

 frequently and closely attached to the substratum, z. e., it was used in 

 much the same manner as a tail, doubtless a consequence of its form 

 and relation to the substratum during movement. But the attach- 

 ment of this part was usually followed or accompanied by the 

 attachment of the other parts of the lateral margins in this region 

 of the body on both sides. This method of use of the parts must 



