no Charles Zeleny. 



Pomatoceros triquetroides were started. It will be remembered 

 that the operculum has a distinct basal suture. In about half 

 of the specimens which were removed from their tubes it was 



found that the oper- 

 culum had been 

 thrown off at this 

 basal suture, the 

 distal portion of the 

 operculum remain- 

 ing in the tube. 

 The plane of the 

 fracture is not a 

 straight one but the 

 middle is pointed 

 forward so as to 

 give in a dorsal 

 view the form of an 

 inverted A. Figs. 

 8b, c; 24c, D, E. 

 Three series of op- 

 erations were car- 

 ried out. In the 

 ■first the operculum 

 was cut in two 

 distal to the basal 

 suture. Here it 

 seems that the part 



J— Ditrupa subulata. Stalk, two days after operation, showing pro- ^^ |.pjg operculum 

 jection of new tissue at one side of basal portion below breaking joint „ UQyg ^^ SUtUte 

 (X20). B — Regenerating operculum of D. subulata, 9 days after . , ,• rr U ^ 



. ,, ^ did not drop ott but 



operation (^X 20;. ' 



C, D, £— Pomatoceros triquetroides. Stages in regeneration of new the regeneration 



operculum from breaking joint level (Xio). C— Operculum just tOolc plaCC by a 



pulled off. D— 3 days after operation. E — 8 days after operation. grOWth frOlTl the 



cut surface. The 

 first sign of this 

 regeneration was a 

 swelling of the terminal region from which three knobs developed, 

 which evidently became the terminal processes of the new oper- 

 culum. The evidence for this change and for the later changes in 

 general is not complete as the later stages were not followed out. 



C 



Fig. 24. 



F — ^Vermilia multivaricosa. Stalk of operculum two days after 

 removal of cup (X 16). Note projecting knob of new tissue at side of 

 stalk. 



