Studies on Regulation. 505 



visible in any of the pieces. These pieces are even more helpless 

 than B. Occasionally they adhere slightly to the substratum 

 and rarely slow progression may occur, though movements of 

 progression are less common than in B. When strongly stimu- 

 lated these pieces usually turn upon the dorsal surface in conse- 

 quence of their irregular muscular contractions and slide slowly 

 over the bottom of the vessel for a time, but finally come to rest 

 and show only slight muscular contractions. 

 Twenty-five days after section: 



A. The two pieces continue active and normal in behavior 

 and the relative size of the new tissue has increased somewhat 

 though each piece as a whole is undergoing reduction. 



B. The behavior of this piece is improving slightly. Though 

 progression occurs only occasionally the piece remains attached to 

 the substratum much of the time. Its movements recall those of 

 Stylochiis; irregular extensions and contractions of parts of the 

 margin occur frequently, and often in consequence of extension 

 and adhesion of the margin the piece becomes somewhat stretched, 

 not merely longitudinally, but laterally as well. Often a general 

 contraction occurs and all attached regions of the margin are 

 stretched. Fig. 44 shows the form of the piece. The relative 

 size of the new tissue has increased (compare Fig. 41) and a small 

 pharynx is present. The margins of the new tissue are somewhat 

 irregular in form since some parts are more extended than others 

 as the piece adheres to the substratum. Some degree of regenera- 

 tion of the ganglia seems to have taken place but it is at all events 

 slight. 



The small size of the pharynx and the slight extent of the in- 

 testinal branches in this piece as compared with A is of interest. 

 The condition of A at this time does not differ greatly from that of 

 a week ago so comparison of the stage Fig. 40 with Fig. 44 will 

 serve to show the differences. 



C. Only two pieces are still alive: these are in much the same 

 condition as before, both as regards behavior and regeneration. 

 Fig. 45 shows the piece noted above, in which the remains of 

 the ganglia protrude from the dorsal surface just posterior to the 

 cut. 



