FORM-REGULATION IN CERIANTHUS. 2/3 



merely of a decrease in length, the tissues remaining normal in 

 appearance except as regards the darker color due to the col- 

 lapsed condition. Later shrivelling of the tips began and con- 

 tinued until only blunt rounded stumps bearing small masses of 

 the dark, shrivelled tissue remained. 



In C. mcinbranaceus a similar reduction of tentacles was 

 observed, both in pieces which were kept open by artificial means 

 and in cesophageal pieces, but in no case did the distal portions 

 shrivel as in C. solitarins. This difference in behavior is probably 

 due to the firmer consistency of the tissues of C. incuibranaccus. 

 In one piece which was opened every day during forty-nine days 

 the marginal tentacles decreased from 4050 mm. to 1015 mm. 

 and the labial tentacles from 20 mm. to 3-4 mm. This piece 

 was then allowed to close and become distended and during the 

 next thirty-nine days the marginal tentacles increased in length 

 to 20 mm. and the labial tentacles to 5 mm. In this case the 

 decrease in length was nearly 75 per cent, for the marginal ten- 

 tacles and about 80 per cent, for the labial tentacles. The 

 marginal tentacles after renewed distension attained nearly 50 per 

 cent, of the original length, the labial tentacles only 25 per cent. 



The oesophageal pieces of C. membranacens were not observed 

 to close aborally across the end of the oesophagus in any case. 

 It was therefore impossible to observe increase in length of the 

 tentacles after reduction in these pieces, but marked reduction 

 was observed in all cases. In one piece the marginal tentacles 

 decreased during twenty-seven days from 60 mm. to 2025 mm. 

 and the labial tentacles from 25 mm. to 1012 mm. and in 

 others a similar reduction was noted. 



It is possible that atrophy of the tips of the tentacles would 

 have occurred if the specimens had been kept for a still longer 

 time. On the other hand this process may be so slow in this 

 species that it is visible merely as a gradual reduction in size. 



In view of these facts there can be little doubt that the length 

 of the tentacles is influenced by the internal pressure. The ques- 

 tion as to whether it is the general internal pressure which exerts 

 this influence, the effect being merely more conspicuous in the 

 tentacles than elsewhere, or whether local pressure due to cur- 

 rents plays a part must be decided by future experiments. 



