FORM REGULATION IN CERIANTHUS. 257 



The problem of " morphallaxis," /. c., the changes in the pro- 

 portions of regenerating pieces leading to the more or less com- 

 plete reestablishment of the "normal" form will be considered 

 elsewhere. 



Fig. 24 shows a regenerated disc and tentacles at a later stage ; 

 in form and general arrangement of parts it is not distinguishable 

 from the normal animal. The marginal tentacles have not yet 

 fully attained their final arrangement ; at present they are in two 

 fairly well marked rows or circles. During the still later stages, 

 however, as further increase in size occurs, the bases of some are 

 forced still farther peripherally and so the characteristic arrange- 

 ment of tentacles is finally acquired. The pigmentation of the 

 marginal tentacles with dark transverse bands, which appears at 

 this stage or earlier, is not shown in the figure. 



THE DIFFERENTIATION OF THE ABORAL END. 



The infolding of the body-wall and the closure of the aboral 

 end of a piece by a thin membrane have already been described. 

 It remains to describe the formation of the characteristic aboral 

 end. The course of regeneration here is much simpler than at 

 the oral end. 



The first marked change from the condition shown in Fig. 14 

 consists in the protrusion in conical form of the thin membrane 

 closing the end (Fig. 25). About the margin of this new tissue 

 the slightly wrinkled margins of the old body-wall are still 

 clearly marked. In Fig. 26 a longitudinal section of the aboral 

 end at this stage is shown. The absence of the aboral pore is 

 to be noted. This new outgrowth at the aboral end does not 

 become well-marked at once after closure, but only after the 

 piece is well filled with water and the regeneration is advanced 

 at the oral end, /. c., it is much slower than oral regeneration. 



In Fig. 27 the aboral outgrowth is seen at a somewhat more 

 advanced stage. The wrinkles and folds upon the margin of the 

 old tissue are gradually disappearing as this stretches and under- 

 goes remoulding. A few days later the wrinkles have disap- 

 peared and there is no sharp distinction between the old body- 

 wall and the new tissue at the time of union. Fig. 28 shows 

 the end at this stage; and it is evident that the margins of the 



