FORM-REGULATION IN CERIANTHUS. 213 



as compared with the highest portion is much greater than the 

 difference in rapidity of regeneration due to difference in level. 



2. The only reason apparent for the difference in rapidity of 

 regeneration on different parts of oblique discs is the difference 

 in the angle between disc and body-wall, which is acute on the 

 upper side of the disc while on the lower side it is obtuse. In 

 consequence of this difference the local pressure exerted by the 

 circulatory currents passing orally in the intermesenterial chambers 

 must be much greater on the upper side of the disc than on the 

 lower. If regeneration is influenced by these currents we should 

 expect delay on the lower side, and it occurs in all cases. 



3. The later equalization in length of the tentacles in pieces 

 with oblique discs is due to the conditions which bring about 

 equality in length of tentacles in normal animals. After the 

 appearance of the tentacles the conditions as regards internal 

 pressure are essentially similar on all parts of the oblique margin 

 and equalization must be expected if the length of the tentacles 

 is determined by internal pressure. 



4. The reduction in the obliquity of the disc in oblique pieces 

 is a compensatory process resulting from the attempt of the 

 animal to orient itself with longitudinal axis vertical and disc 

 horizontal. In the attempt at orientation unequal contraction of 

 the muscles on different parts of the circumference occurs, and 

 its continuation brings about changes in the tissues which lead 

 gradually toward the establishment of the typical form. The 

 form is the result, not the cause of the reaction. 



5. In pieces cut wholly within the cesophageal region the two 

 cut ends of the oesophagus usually unite with the cut ends of the 

 body-wall, thus leaving the oesophagus open to the exterior at 

 both ends. This method of closure isolates each intermesenterial 

 chamber completely and prevents any direct communication 

 between the enteron and the exterior. 



6. Such oesophageal pieces become slightly distended at first 

 in consequence of diffusion of water through the walls, but since 

 the oesophagus is not in communication with the enteron the 

 internal pressure remains far below that of the normal animal. 

 Regeneration of the marginal tentacles begins in such pieces, but 

 never proceeds beyond the formation of mere buds. 



