484 C. M. Child 



Harenactis I suggested that the contraction was due primarily 

 to a difference in the elasticity of the different layers of the body- 

 wall, though undoubtedly complicated and modified by other 

 factors (Child '04a, pp. 55-65). It is possible the physiological 

 as opposed to the purely mechanical aspects of this reaction were 

 not sufficiently emphasized in that paper, though my work on 

 Harenactis has not brought about any essential modification of 

 my views concerning this point. Here, as in Cerianthus, the in- 

 rolling of the body-wall which follows a wound may be interpreted 

 as the result of a difference in elasticity of the different layers of 

 the wall, though it is probable that the physical condition of the 

 wall may be altered by various conditions, including the wound 

 itself. 



But the point which seems to me of greatest importance is that 

 the reaction does not appear to possess an adaptive character, 

 either in Harenactis or in Cerianthus. Attention was called to 

 this point in my earlier paper (Child '04a, pp. 62-65), but a brief 

 further consideration seems desirable. I am unable to find any 

 basis for the conclusion that the contraction following the wound 

 is an adaptive reaction directed tow^ard bringing the cut margins 

 together and so producing conditions which permit the closure 

 of the wound. Closure may be prevented even more easily in 

 Harenactis than in Cerianthus by the form or position of the wound. 

 In ever}' case where a wound is made the wounded surfaces of 

 the tissues contract, whether closure of the wound results from 

 contraction or not. Whether the wound is closed and how it is 

 closed depend, not upon the contraction which follows the wound, 

 but upon the conditions under which that contraction occurs. In 

 the above consideration of the mesenteries, the oesophagus and 

 the mass of the enteric organs as factors in the closure it is suffi- 

 ciently evident that the contraction may lead to very different 

 results under different conditions. In the oesophageal region, for 

 example, union of the body-wall and oesophagus occurs (Fig. 7, 8, 

 II ), not because this is the process best fitted to bring about return 

 to the "normal form," but because any other method of closure 

 is physically impossible under the conditions. The contraction 

 of the cut mesenteries must bring the margin of body-wall and 



