FORM-REGULATION IN CERIANTHUS. 145 



A similar splitting of the aboral end was accomplished in 

 Series 19 and 38 - - 6 and 4 pieces respectively. Three of these 

 pieces produced specimens with double aboral end, but in the 

 remainder the two parts united more or less completely. In 

 these series delay in union of the cut surfaces also occurred, and 

 whenever the presence of openings prevented distension the ten- 

 tacle-regeneration was delayed, proceeding only when distension 

 took place. 



In several series the attempt was made to prevent union of cut 

 surfaces at the aboral end by making the cut surface very irregular 

 in form, splitting it into strips, making oblique cuts in it, remov- 

 ing portions, etc., the object being to bring about independent in- 

 rolling of different parts and thus prevent the complete closure of 

 the end by new tissue. These experiments were not very effec- 

 tive, however. A greater or less delay in closure and a conse- 

 quent delay in tentacle-regeneration was brought about, but in 

 nearly every case closure took place within two or three weeks 

 and after that regeneration proceeded in the usual manner. 



GENERAL CONSIDERATIONS. 



It is, I think, sufficiently demonstrated by the forgoing experi- 

 ments that there exists a close relation between internal water- 

 pressure and tentacle-regeneration. In order, however, to meet 

 possible objections and to render more clear certain points a brief 

 discussion of the results is necessary. 



The objection may be made that the operations are severe 

 enough to produce some pathological effect upon the pieces 

 which prevents or retards their regeneration. Any objection of 

 this nature is abundantly refuted by the data of the experiments 

 themselves, from which it is clear that just as soon as the enteron 

 is capable of holding water under some degree of pressure the 

 course of regeneration becomes typical, and that even where the 

 regeneration has been delayed for one or two months it is as 

 complete when it does occur as if it had taken place immediately 

 after section, although the resulting animal is smaller. Of course 

 where the pieces are kept without food for periods of three or 

 four months or more they become greatly reduced in size and 

 their capacity for regeneration is diminished ; nevertheless, even 



