FORM-REGULATION IN CERIANTHUS. 211 



admitted it follows that less water would enter these pieces and 

 less distension would occur than in pieces aboral to the oesoph- 

 agus. If the internal pressure affects tentacle-regeneration, less 

 regeneration would occur in consequence of this slight disten- 

 sion in cesophageal pieces than in others where distension is 

 greater, and this is actually the case. 



It was noted that the pieces in which the oesophagus remains 

 open aborally gradually collapse again in the course of a week 

 or two. This collapse is probably due to a slow loss of the fluid 

 which first caused the distension. If the body-wall is slightly 

 permeable for substances in solution in the enteron the distension 

 produced at first will gradually diminish since in consequence of 

 continued starvation the amount produced gradually decreases. 

 Whatever the exact nature of the process may be, a decrease in 

 the distension occurs. As this process continues the regenerat- 

 ing tentacles also decrease in size instead of continuing to grow. 

 This fact is important as showing the apparent close relation 

 between tentacle-regeneration and internal water-pressure. In 

 pieces cut below the oesophagus the regeneration of the mouth 

 and the entrance of water through it serves not only to prevent 

 decrease in the internal pressure but to increase it, and further 

 growth of the tentacles takes place. 



The most striking feature of the experiments is the difference 

 in behavior as regards regeneration between the pieces in which 

 the body-wall closes aborally across the oesophagus and those 

 in which the cesophagus remains open aborally to the exterior. 

 The pieces of the first kind begin to regenerate typically as soon 

 as the closure occurs, while the others never produce anything 

 more than marginal tentacles 1-2 mm. in length. In the intro- 

 ductory description of these experiments it was shown that in 

 case of closure the connection between the aboral end of the 

 body-wall and the cesophagus is severed and the oesophagus 

 opens into the enteron (Figs. 1214). The breaking of this con- 

 nection, z'. e., the change from the condition shown in Fig. 13 to 

 that of Fig. 14 is probably itself due at least in part to internal 

 water-pressure, though the manner of its occurrence cannot be 

 observed. Other factors, such as a difference in rapidity of 

 growth or a difference in resistance between the tissue of the 



