FORM REGULATION IN CERIANTHUS. 115 



the number of aboral tentacles increased (Fig. 18, December 28) 

 though the piece as a whole was undergoing reduction in size. 

 Fig. 23 represents the section at this stage. 



The other piece in which aboral tentacles developed is shown 

 in Fig. 24 as it appeared two months after the operation (Novem- 

 ber 20). The method of closure in this piece differs somewhat 

 from that occurring in the first : Figs. 26-28 illustrate this point. 

 It will be seen that the aboral end of the body-wall bent orally 

 much further than in the first piece (cf. Figs. 19 and 26), but 

 also united with the aboral end of the oesophagus. It is probable 

 that the piece was longer than the preceding. The difference in 

 method of closure is readily accounted for by such difference in 

 length. At the stage shown in Fig. 24 the aboral tentacles were 

 beginning to develop. Fig. 28 is a diagrammatic section of this 

 stage. Figure 25 represents a side view of the piece a month 

 later (December 28). As the figure shows, the large tentacle in 

 the middle arose just over the region where the body-wall folded 

 longitudinally upon itself. (The shading of the body-wall repre- 

 sents the longitudinal striping.) All tentacles to the left of this 

 large tentacle are upon the oral end of the piece, and all to the 

 right are aboral. Six aboral tentacles appeared on this piece in 

 addition to the single tentacle which can scarcely be regarded as 

 either oral or aboral. In this case, as in the preceding, the aboral 

 tentacles arose either from the oesophagus or from the line of 

 union between it and the body-wall (Fig. 28). 



Figs. 19-23 and 26-28 show that reduction of the body- wall 

 is more rapid than reduction of the cesophageal region. This 

 difference is probably correlated with functional differences in 

 the tissues. Normally the body-wall is subjected to greater ten- 

 sion than the oesophagus, for the two sides of the latter are sim- 

 ply appressed during distension of the body. This being the 

 case, it follows that conditions of tension depart less widely from 

 the norm for the oesophagus than for the body-wall in these 

 pieces, hence the more rapid change in the latter. 



General Considerations. 



These aboral outgrowths have been called tentacles for, in my 

 opinion no ground exists for believing that they are anything 



