Factors of Form Regulation in Harenactis Atteniiata 501 



folded and greatly reduced in size. There is no doubt that a 

 greater or less degree of atrophy occurs in the most compressed 

 regions: if the period of collapse is sufficiently long the local atro- 

 phy may bring about complete disappearance of certain mesen- 

 teries. When distension occurs and tentacles develop the ten- 

 tacles corresponding to these mesenteries will be absent, or if the 

 mesenteries reappear after the normal functional conditions are 

 reestablished, these tentacles may develop later, and perhaps 

 remain of small size for a longer or shorter time. In short, these 

 cases of local absence or retardation of development of tentacles 

 in short proximal pieces are the result of local reduction or atrophy 

 of body-wall and mesenteries which in turn is the result of com- 

 pression or of absence of tension in wrinkled or folded regions of 

 collapsed or almost collapsed pieces. 



As regards regional localization of these phenomena in the 

 body, irregular reduction in number and size of tentacles may occur 

 at any level of the body if the proper conditions arise, but in pieces 

 from the more distal regions closure and distension usually occur 

 so rapidly, if they occur at all, that there is no time for atrophy 

 such as occurs in these proximal pieces. 



Regular reduction to half the number of tentacles has been 

 observed only in the two proximal pieces above described (fig. 23), 

 but, as was shown in preceding sections, the course of restitution 

 in small pieces from other regions of the body is so highly modified 

 bv the presence of the oesophagus in the more distal regions and 

 the large mass of enteric organs in other regions that it is impos- 

 sible to obtain any accurate data as to the physiological capacities 

 of these regions. It is probable, however, that the mesenteries, 

 and especially those of the second cycle disappear more readily 

 in the proximal regions of the body than elsewhere, because 

 they are much smaller and less highly differentiated there than 

 elsewhere. 



IV GENERAL CONSIDERATIONS 



It has been pointed out above that the contraction following the 

 wound is not adaptive in character; apparently it is merely the 

 direct result of the stimulus of the wound, and it occurs in essen- 



