FORM REGULATION IN CERIANTHUS /ESTUARII. 29 



Specimens normally distended are also very sensitive to light : if 

 kept in covered dishes sudden exposure even to diffuse daylight 

 produces marked general contraction after a short latent period. 

 As regards this stimulus also collapsed specimens or pieces are 

 much less sensitive than those which are distended with water. 



The distension of the body and the erection of the tentacles is 

 accomplished in this species as in C. solitaruis by the entrance 

 of water into the enteric cavity, both through the mouth and 

 through the body-wall. The entrance of water through the 

 body- wall probably occurs at all times to a greater or less ex- 

 tent, but is most readily observed in pieces undergoing regula- 

 tion in which the ends have closed but no mouth has formed 

 (cf. Child, '041^, p. 267 et seq.). 



I. The Course of Form-Regulation. 



In pieces above a certain minimal size, isolated by transverse 

 cuts, the course of collapse and inrolling of the body- wall in the 

 region of section, the closure of the wound and the formation 

 of new tissue are in general similar to those processes in C. soli- 

 taniis (Child, '03^, pp. 244-257, Figs. 1-24). As regards the 

 formation of new tissue at the aboral end there is a quantitative 

 difference between the two species, the amount of new tissue 

 formed in C. cvstuarii being usually much less than in C. solitavius 

 (Child, '03^, pp. 257-259, Figs. 25-31). Attention may be re- 

 called to the fact that the marginal tentacles in C. solitarius do 

 not arise at the cut surface itself, but a short distance aboral to 

 it (Child, '03^, p. 252, Figs. 10-19). the first indications of their 

 formation being a reduction in the thickness of the body-wall 

 in this region and the formation of a crenated ridge around the 

 end of the piece, followed by the outgrowth of a tentacle above 

 each interseptal chamber. These processes follow a similar 

 course in C. cBstnarii. 



One difference between the two species may, however, be noted 

 in this connection : in C. cestitarii the inrolling of the body-wall 

 is much less regular than in C. solitarius, and closure in the usual 

 manner is retarded or prevented more often in the latter species 

 because the formation of the thin membrane closing the cut end 

 is impossible. In consequence of the lack of firmness and stiff- 

 ness in the body-wall of C. astJiarii the pieces often assume very 



