146 C. M. CHILD. 



such pieces as these show very clearly the result of internal 

 pressure. A good example is the piece of Series 1 1 shown in 

 Fig. 1 1 and the last pieces of Series 28. 



In the preliminary survey in the preceding paper (Child, '04$) 

 it was suggested that not only does the rapidity and amount of 

 tentacle-regeneration depend to a greater or less extent upon the 

 internal water-pressure, but the position of the regenerating mar- 

 ginal tentacles may be determined by the local pressure upon the 

 inrolled oral end of the piece caused by the circulatory current 

 which moves orally in the peripheral part of each mesenterial 

 chamber and thus continually forces water into the blind sac at 

 the oral end produced by the inrolling of the body wall and the 

 mesenteries bounding each chamber. According to this view 

 the tissue reacts to this local change in pressure by local growth 

 and the position of the new marginal tentacle is determined. 

 The first visible changes leading to regeneration consist in the 

 reduction in thickness of the body-wall in consequence of the 

 disappearance in large part or completely of the longitudinal 

 muscle-layer. The local area of thin tissue being thus formed, 

 it is effected both by the local pressure due to the circulatory 

 current and by the general internal pressure. Both of these fac- 

 tors subject the area to tension and, as in other areas of thin 

 "new" tissue (see the section on "The Closure and Distension 

 of Pieces " in the preceding paper, Child, '04^), growth is the 

 result. 



A few tentative suggestions based upon the preceding data are 

 added here in order to indicate the bearing of certain features of 

 the experiments upon this hypothesis. But first of all the fact 

 should be emphasized that water-pressure constitutes in any case 

 only one factor in a complex process ; it is impossible to doubt 

 its influence in view of the experimental data, but recognition of 

 the role played by water-pressure does not constitute a complete 

 solution of the problem of form-regulation in Cerianthus. 



It should be borne in mind that complete elimination of local 

 water pressure due to currents has not been accomplished in any 

 of the experiments. The methods employed have succeeded in 

 bringing about a more or less complete reduction of the general 

 distension of the body by water but the local circulatory currents 



