462 WAYLAND M. CHESTER 



and in some cases was closed within a half hour, though in many 

 experiments it took five or six hours. Viewed by transmitted light 

 under low magnification, the dark endoderm at the cut end 

 appeared contracted for a distance that corresponded to the length 

 of the nipple on an attached stump. The ectoderm of the same 

 region was white and opaque, the opacity diminishing peripherally 

 as in the stump end. On the second day the distal ends of the 

 fragments were closed and rounded (fig. 5, a and b) . The activity 

 at the distal ends of excised pieces is therefore much the same as 

 that in the end of a stump. At the distal end of an excised frag- 

 ment three is a muscular contraction corresponding to the tempo- 

 rary muscular closure in the stump. But the sphincter in the 

 fragment does not close so tightly and a nipple is not often found. 

 A structural closure occurs similarly in the stump and the distal 

 tips of the fragments (compare figs. 2 and 5). 



In order to compare further the behavior of distal cut ends when 

 the tentacle is attached and when it is free, I performed the fol- 

 lowing experiment a number of times with uniform results. A 

 piece of tentacle was cut off and when the stump had formed its 

 nipple, the end with the nipple was cut off and allowed to fall to 

 the bottom of the dish. The fragment collapsed and the nipple 

 disappeared. When this fragment of tentacle had partially ex- 

 panded the distal end became more rounded, like the distal cut 

 end of a tentacle whose tip had been cut off after the tentacle was 

 severed from the animal. As in such a distal cut end, the walls 

 were opaque and slightly constricted. 



Polarity is shown in the difference of activity of the proximal 

 and distal cut ends. While on the attached stump a temporary 

 muscular nipple was formed within half an hour after cutting, 

 there was no evidence of such closure at the proximal end of the 

 free tentacle (fig. 4, a). The end was open, a condition sharply 

 contrasted with that of the closed nipple which marked the other 

 cut end resulting from the same cut. The slight inrolling seen 

 in the stimip immediately after cutting was seen here also, but 

 the opening was irregularly outlined and the wall was wrinkled, 

 sometimes deeply so. Figure 4, a, shows such an end, six hours 

 after the cut was made. Twenty-three hours after the cut was 



