FORM REGULATION IN CERIANTHUS. 245 



THE IMMEDIATE EFFECTS OF THE OPERATION. 



Individuals which were in good condition and well extended 

 were chosen and the cuts were made rapidly with sharp scissors. 

 All parts of the body contract strongly in consequence of the 

 cut, and of course total collapse of the piece occurs, owing to 

 the escape of the water from the enteric cavity. Within a few 

 moments the piece may relax somewhat from the extreme condi- 

 tion of contraction, but does not attain anything like its original 

 length. Placed in the jar it lies on the bottom, and the weight 

 of the tissues causes it to become more or less flattened. The 

 piece has no power to retain its cylindrical form, though the 

 mesenteries and mesenterial filaments, especially in pieces cut 

 from the oral half of the body, partly fill the enteron and so 

 cause the piece to retain a more or less rounded form. The 

 body-wall is opaque in these pieces, while in normal specimens 

 distended with water it is slightly translucent. The opacity is 

 due simply to its greater thickness in the absence of the tension 

 caused by internal water-pressure. 



Within a few moments after section the cut edges at the two 

 ends of the piece begin to bend or roll inward, and in an hour or 

 two this inrolling has proceeded so far that the cut edges are no 

 longer visible from the ends and the opening is almost completely 

 closed by the inrolled portions. In Fig. 2 a longitudinal section 

 through the oral end of such a piece is shown, the ectoderm and 

 entoderm being indicated by full black lines and the thick mus- 

 cular layer by fine lines. In this and following figures of the 

 same kind the mesenteries are not shown ; they of course occupy 

 practically the whole of the enteric cavity after collapse. A sec- 

 tion through the aboral end shows conditions similar to those 

 figured in Fig. 2. 



In consequence of the infolding about the whole circumference 

 of the cut ends the circumference of the body-wall in the infolded 

 region decreases greatly, although the transverse contraction of 

 the body- wall during the infolding is not marked. It is, therefore, 

 thrown into numerous longitudinal folds and ridges at the edge, 

 and these appear when the piece is viewed from the end as folds 

 and ridges radiating from what remains of the central opening. 



