FORM REGULATION IN CERIANTHUS .■ESTUARII. 3 I 



and a thin membrane of new tissue is formed, whose size is 

 dependent in part on the degree of tension existing. When 

 pieces are cut in such shapes, c. g., by longitudinal or zig-zag 

 cuts, etc., that the cut margins or parts of them do not come into 

 contact with each other, the outgrowth of new tissue does not in 

 any case occur from the free cut surfaces. Such pieces may 

 remain open indefinitely and fail completely to replace the parts 

 removed. 



In many cases after the growth of new tissue has begun between 

 approximated parts of the cut surface the new tissue may grad- 

 ually extend for a very short distance over the cut surface on each 

 side of the point where it began to grow. In such cases it can 

 readily be determined that the thin new tissue is itself under some 

 slight degree of tension. Under these conditions growth proceeds 

 to a certain point and then stops. Apparently the mechanical 

 conditions in the region involved and the physical properties of 

 the new tissue itself are important factors in determining the 

 amount of growth. In my earlier experiments the fact was noted 



2 



that such growth occurs to a much greater extent in C. ineni- 

 branaceus where the new tissue is much thicker and more resist- 

 ant than in C. solitarius (Child, 'OA,a, pp. 70-71). In C. ccstuarii, 

 where the tissues are even more delicate such growth of new tis- 

 sue does not occur to any great extent. In Fig. 2 the end of a 

 piece cut so that it remains widely open is shown and the extent 

 of the growth of new tissue is indicated by the shaded areas in 

 the angles of the inrolled margins. Such a piece never closes 

 by extension of the new tissue over the whole opening, but remains 

 indefinitely in the condition figured, unless the relation of the parts 

 of the cut margin is altered by changes in the degree of contraction 

 or by passive changes of the position ofthe piece, which bring new 

 portions of the cut margins into contact or proximity. After 

 such a change growth of new tissue may continue for a time 

 where the angle between two adjoining parts of the cut margin 

 is not too great, but in no case does the new tissue extend with 



