child] iX/KM-REGULATIOM IN CCELENTEKA AND i URBELLARIA I4I 



certain ahgle, the closure of wounds can be experimentally pre- 

 vented or stopped at any point. The relation between extent of the 

 new tissue between diverging cut surfaces and the angle of diver- 

 gence of these surfaces, as well as the concave free margin of such 

 new tissue are comparable with the behavior of fluid films under 

 similar conditions. This new embryonic tissue certainly contains a 

 high percentage of water, and it is not at all improbable that the 

 laws of capillarity should determine its behavior to a greater or less 

 extent. 



The second point of importance in the experimental analysis of 

 regeneration concerns the influence of water-pressure on regener- 

 ation. As is well known, Cerianthus is essentially a hollow sac with 

 a mouth at one end ; the sac is divided peripherally into chambers by 

 the mesenteries ; a hollow marginal tentacle opens orally from each 

 one of these chambers, and most of them commimicate also with a 

 smaller labial tentacle. Under normal conditions, and when undis- 

 turbed, the body and tentacles of the animal are distended by the 

 water in the enteron, which is under a considerable degree of pres- 

 sure. When a cut is made in the body-wall, or a piece is removed, 

 collapse of body and tentacles occurs at once. As I shall show in 

 detail elsewhere, this is due simply to escape of water from the 

 enteron and not at all to a change in osmotic conditions, as Loeb^ 

 believed. Typical regeneration of pieces can never occur unless the 

 piece can in some manner acquire again the form of a sac in which 

 water can be retained under pressure. If closure of the aboral end 

 of pieces be prevented by repeated artificial separation of the cut sur- 

 faces, the appearance of the tentacles at the oral end is delayed. If 

 the piece be allowed to close until small tentacle-buds have ap- 

 peared, and then be opened at the aboral end and kept open, growth 

 of the regenerating tentacles ceases, and they may even decrease in 

 size. In every case the delay or inhibition continues as long as an 

 opening is present which prevents distension of the body by water 

 and pressure upon its walls. As soon as the openings are allowed 

 to close, the interrupted regeneration continues. The objection may 

 be made that the pressure of the water in the enteron will be the 

 same in all regions of the body, and that it cannot account, therefore, 

 for the localization of organs at certain regions. To this the answer 

 may be made that currents in definite directions are caused in the 

 enteron by the vibrations of cilia and that these currents striking 

 the wall at certain points may produce characteristically localized 

 differences in pressure. It is highly probable, as I shall show else- 



Untersuchungen zur physiologischen Morphologic, i, 1891. 



