FORM REGULATION IN CERIANTHUS. 247 



by the body-wall. In most cases, however, as the collapsed, 

 more or less flattened piece lies on the bottom of the jar the in- 

 folding edges come into contact along the longer margins as in 

 Figs. 3 and 4, leaving an elongated slit between them. In other 

 cases the closure may occur as shown in Fig. 5. In general the 

 form of the end depends wholly upon physical conditions and 

 especially on the form of the transverse section of the piece after 

 collapse. 



The infolding of the cut margins is undoubtedly the result of 

 mechanical conditions, though these conditions may themselves 

 be in part reactive in nature. As Loeb has pointed out, an in- 

 folding must occur if the inner portions of the body-wall are 

 under greater longitudinal tension than the outer portions. Such 

 a condition may possibly be produced in the muscles near the 

 cut, the inner layers undergoing greater contraction than the 

 outer, but the elasticity of the fibrillar mesogkea is probably in 

 part responsible. As will be shown later this infolding produces 

 in many cases conditions from which a return to the normal form 

 is impossible. It can scarcely be regarded, therefore, as an 

 adaptive reaction in the stricter sense. The radiating wrinkles 

 and folds upon the end are due simply to the fact that the cut 

 edges do not contract transversely as they are folded in. 



As already noted, the result of the infolding is to close the 

 terminal openings more or less completely. The closure is in 

 no case perfect since between the irregular wrinkles there are 

 always numerous interstices which afford communication between 

 the enteron and the exterior. In most cases, however, these 

 are soon blocked by the tenacious slime secreted by the ectoderm 

 and are also frequently more or less completely filled by portions 

 of the mesenteries or the filaments which happen to extend 

 through them from within. 



THE CLOSURE OF THE ENDS. 



The histological changes about the cut margins have not been 

 fully investigated as yet, but it has been determined that growth 

 of new tissue upon the edges v begins soon after the cut is made. 

 If after one or two days the infolded end be opened and carefully 

 spread apart a very thin and delicate whitish membrane of new 



