FORM REGULATION IN CERIANTHUS. 2OI 



My suggestions regarding the possible role of local pressure in 

 bringing about the characteristic result in oblique pieces should 

 be considered merely as an attempt to indicate how differences of 

 local pressure may be effective here. The hypothesis must be 

 applied to as many cases as possible before definite conclusions 

 are reached. For the labial tentacles my data concerning local 

 pressure are incomplete, as was pointed out in a previous paper 

 ('04/7). At present, however, I do not see any other probable 

 explanation of the delay in the regeneration of the marginal ten- 

 tacles on the lower portion of an oblique disc than that suggested 

 above. 



The gradual equalization in the length of the tentacles and the 

 gradual reduction in the obliquity of the disc which are always 

 features of the later history of oblique pieces, lead toward the 

 establishment of symmetry and the typical form. Is there any 

 satisfactory interpretation of these changes or must they be 

 regarded for the present as inexplicable ? They resemble in 

 character certain of the phenomena which have led Driesch to 

 assume the existence of an autonomistic principle or entelechy 

 governing form. But I am convinced that an interpretation of an 

 entirely different sort is possible. 



In the first place it is necessary to recognize that the equaliza- 

 tion of the tentacles and the reduction in obliquity of the disc are 

 two wholly distinct phenomena due to wholly different factors. 

 The equalization in length of the tentacles is the result of the 

 same factors which cause the regeneration of tentacles of a cer- 

 tain length in typical transverse pieces and which bring about 

 approximate equality in the length of tentacles in normal animals. 

 If internal pressure plays a role in the latter cases, undoubtedly 

 it is equally important in the former. Considering the oblique 

 pieces, it is clear that as soon as the tentacles on the lowest part 

 of the margin begin to grow conditions for their further growth 

 are similar, as regards internal pressure and circulatory currents, 

 to the conditions on the opposite margin. Each tentacle-bud 

 forms a blind sac whose walls are growing tissue. Conditions of 

 internal pressure in this sac do not differ on different parts of the 

 margin, whatever the angle between disc and body-axis. The 

 appearance of the tentacle-buds is delayed upon the lowest part 



