474 C. M. Child 



of all parts of the body. Usually it results in a decrease in the 

 size of the opening made by the wound, but it is not at all difficult 

 to cut the body-wall in such manner that closure of the wound is 

 impossible because of the contraction which occurs. In these 

 cases the wound reaction occurs in exactly the us.ual manner, but 

 the conditions of the experiment determine the character of the 

 result as regards closure or non-closure of the wound. The case 

 is very similar to that of Cerianthus which was considered in an 

 earlier paper (Child '04a). In both species, as well as in many 

 other actinians, the same reaction which brings about closure of 

 the wound in certain cases, renders it impossible in others. Under 

 certain other conditions closure of the wound may occur in such 

 manner that return to the usual form is impossible (Child '04d, 

 pp. 205-207; '08b, pp. 41-45)- 



The actual closure of the wound by new tissue is the result of 

 proliferation and growth of cells adjoining the cut surfaces of the 

 body-wall mesentery or other organ. But in Harenactis, as in 

 Cerianthus (Child '04a, pp. 66-74, '04b, pp. 276-279, '08, pp. 

 30-32), the outgrowth from a cut surface of new tissue with a free 

 margin does not occur to any appreciable extent except under 

 certain special conditions. This point cannot be too strongly 

 emphasized since it is one of the most important features of regu- 

 lation in these and many other actinians. In the papers referred 

 to above, I have shown that the growth of the new tissue begins 

 in the angles of the inrolled portions of the cut surface, and also, 

 and this is the most important point, that it ceases almost imme- 

 diately unless the tissue is subjected to some degree of stretching 

 or tension. The indefinite outgrowth of new tissue from a cut 

 surface until it meets new tissue growing out from another surface 

 does not occur in these forms. In short we may say in general 

 terms that the growth and differentiation of neiv tissue in the body- 

 wall, the tentacles and the mesenteries is possible only when the 

 regions concerned are subjected to a certain degree of mechanical 

 tension or stretching. It is unnecessary to cite at length the data 

 concerning this point for Harenactis since they are quite similar 

 to those presented in my earlier papers for Cerianthus. Closure 

 of the wound in Harenactis as in Cerianthus can occur only under 



