Factors of Form Regulation in Harenactis Attenuata 483 



some of these cases the mesenterial organs which were extruded 

 are again drawn into the enteron and the cut end closes over them 

 without any marked delay or other departure from the usual 

 method. 



Since the degree of contraction of the body-wall following a 

 wound is in some degree proportional to the intensity of the stim- 

 ulus, pieces cut at both ends extrude their mesenterial organs more 

 frequently and to a greater extent than those with one end intact. 

 Not infrequently, if contraction is considerably greater or more 

 rapid at one end than at the other such pieces turn completely 

 inside out. In this position regulation in the usual manner is of 

 course impossible, and so far as I am aware, pieces which have 

 turned inside out do not succeed in turning back again, but remain 

 in this position until death occurs. 



As was noted above in Section i, even the oesophagus may be 

 forced out of the end of the piece in some cases : this occurs only 

 in short pieces within the oesophageal region, i.e., in which the 

 body-wall and oesophagus are cut at both ends (e.g., pieces between 

 levels a and h. Fig. 2). If the oesophagus is cut away such pieces 

 form rings; if it remains, closure of the wound and restitution are 

 impossible. 



The mass of the enteric organs is a much more important factor 

 in determining the occurrence or non-occurrence and the method 

 of restitution in Harenactis than in Cerianthus where these organs 

 are relatively much smaller and very rarely protrude from a cut 

 end. 



^ The Nature and Significance of the Wound-Reactions 



It is evident that the contraction of the cut surface which follows 

 a wound is a general property of the tissues of Harenactis. It is 

 not in all cases simply a muscular contraction, for it may occur 

 in regions where muscle fibers are not differentiated or at right 

 angles to the direction of the fibers. Of course where muscle 

 fibers are injured, they become involved in the reaction. In the 

 case of Cerianthus, where the wound reaction is also apparently 

 independent of muscle fibers and otherwise very similar to that in 



