32 C. M. CHILD. 



a free margin across wide spaces as in C. nicnibranaccus (Child, 

 'o4rt, Fig. 31). 



If the piece becomes distended with water after closure of a 

 cut end by new tissue the new tissue, which at first is scarcely 

 visible between the margins of the old parts, increases in area, 

 but in the absence of distension such growth never occurs. Fig. 

 3 on p. 277 of my earlier paper (Child, 'OAfU) shows the growth 

 of new tissue in a collapsed piece of C. so/itm-ius and Fig. 4 the 

 growth in a distended piece. The differences in C. ccstuarii are 

 similar. 



There is then no escape from the conclusion that mechanical 

 strain is a necessary factor in the growth of new tissue in these 

 species. That it is the only factor, I should be the last to assert, 

 but I think it is sufficiently clear that in its absence the Cen- 

 aiitJius material possesses no inherent power to restore missing 

 parts. 



II. The Control of Tentacle-Development in Regulation. 

 {a) By Artificial Openings iji the Body- Wa/l. 



After the closure by new tissue of the ends of pieces distension 

 of the enteric cavity with water occurs before any opening into 

 the enteron exists. The passage of the water through the body- 

 wall is probably not a simple osmotic process but something 

 more complex. When the mouth is present or after a new 

 mouth is formed water may enter through it, and by these means 

 a certain degree of distension is maintained. In my experiments 

 with C. solitarius it was possible to prevent, at least in large 

 measure, this distension by making openings in the body-wall 

 and reopening them at short intervals (Child, '04^). Under these 

 conditions the development of the tentacles is retarded or almost 

 entirely inhibited. 



The secretion of slime about the opening and the inrolling of 

 the margins of the cut make it impossible to prevent all dis- 

 tension, but by removing the slime and reopening the pieces every 

 few hours or even once a day the distension can be reduced far 

 below the normal and the first appearance and the rapidity of 

 development of the tentacles greatly retarded and their final size 

 much reduced. If it were possible to eliminate all internal pres- 

 sure the tentacles would undoubtedly fail to appear. 



