FORM-REGULATION IN CERIANTHUS. I 2Q 



inrolled margins to permit escape of the water from the enteron. 

 From what has been said above regarding the rapidity of infolding 

 of the margins and the closure by means of slime, it is evident 

 that this reopening must be frequent if the establishment of water- 

 pressure in the enteron is to be entirely prevented. In the course 

 of my experiments of this kind it was found practically impos- 

 sible to prevent closure by approximation of the margins and 

 plugging of the opening with slime between the times of opening. 

 Pieces in which the mouth had regenerated, thus permitting rapid 

 entrance of water, were often found more or less distended with 

 water after being left over night. Frequently even a shorter time 

 than this was sufficient to permit provisional closure and the 

 establishment of more or less pressure in the enteron. It is clear 

 therefore that unless such pieces are reopened at very short 

 intervals --one to two hours the establishment of some degree 

 of water-pressure in the enteron cannot be prevented in many 

 cases. It was impossible for me to reopen the pieces every hour 

 or two during several days or weeks, consequently in no case 

 was it possible to eliminate entirely water-pressure in the enteron. 



As a matter of fact, however, the water-pressure in a piece in 

 which one end is closed only by approximation of the margins 

 and plugging of the crevices with slime is in most cases much 

 below the pressure in normal animals, as could be readily deter- 

 mined by the resistance of the body- wall, the degree of disten- 

 sion, etc. It follows from this fact that pieces whose aboral ends 

 are repeatedly opened and not allowed to close definitively by the 

 formation of new tissue will be subjected to much less pressure 

 than those allowed to close in the usual manner. It is possible 

 then to reduce the enteric pressure if not to eliminate it entirely, 

 and as my experiments will show, the reduction in pressure has 

 a marked effect. In my experiments, the pieces were opened at 

 intervals of from two days to half a day. 



Except where statement to the contrary is made all experi- 

 ments described here were performed on Ccriantlius solitaries. 

 Each series retains the number given it in my notes and the date 

 of each observation is given. Comparison of the control pieces 

 will show wide differences in the rapidity of regeneration in 

 different series, due of course to the temperature of the water at 

 the time of experiment (cf. Child, '03$). 



