FORM REGULATION IN CERIANTHUS. 57 



of the piece as it lies on a flat surface. In pieces of this kind 

 complete collapse and contact of the body-walls is prevented by 

 the large mass of mesenteries and mesenterial filaments which 

 occupy the enteron. These are not represented in the figures, 

 but they fill the whole enteron after collapse. Any solid mass 

 in the enteron would of course have the same effect. 



A piece cut from the extreme aboral end of the body (Fig. 4) 

 differs in certain respects from the piece just described. Figs. 5 

 and 6 show the changes in a piece of this kind. Here the cut 

 end becomes rolled inward to a much greater extent than in the 

 previous case so that the enteron is nearly filled by the inrolled 

 portion and the cut surface is so situated that closure by growth 

 of new tissue from this surface is impossible. The reason for the 

 greater degree of rolling in this piece as compared with the longer 

 piece is undoubtedly to be found in the absence of mesenteries, 

 except a single pair, in the aboral region. Since the enteric 

 cavity is not filled with a mass of mesenterial filaments as in a 

 region further orally the inrolling continues until the entire cavity 

 is practically obliterated by the inrolled parts. 



If a cut be made in one side of the body or a piece removed as 

 in Fig. 7, the cut edges roll inward as in other cases, but in addi- 

 tion to this the body becomes bent at the level of the cut, so that 

 here also the inrolled edges are brought into contact (Figs. 8 

 and 9). 



The widest departures from the typical form are found, how- 

 ever, in those pieces which were cut longitudinally as well as 

 transversely. In these the results differ to some extent accord- 

 ing to the shape and relations of the pieces. Fig. 10 represents 

 a cylindrical piece split longitudinally on one side. One form 

 after collapse and inrolling of cut margins is shown in Fig. n. 

 Fig. 12 represents a transverse section and Fig. 13 a longitudinal 

 section of one end. In Fig. 14 another form of closure is rep- 

 resented ; here the ends fold over to a greater extent so that the 

 opening is entirely on one side of the piece. Fig. I 5 represents 

 a transverse section of this piece and Fig. 16 a longitudinal sec- 

 tion in the plane indicated by the vertical line in Fig. 14. 



In most cases, however, the right and left longitudinal cut 

 edges do not roll inward with equal rapidity and the result is 



