28O C. M. CHILD. 



enterics regenerate and the series thus becomes complete. Still 

 nearer the aboral end only a few mesenteries are present on the 

 directive side, and finally only a single pair. In most of the 

 pieces from this region regeneration of the mesenteries does not 

 occur, probably because of the decreased reactive capacity of the 

 tissues in this region, as has been suggested (Child, 'o.^b). In 

 certain pieces from this region the regeneration of tentacles cor- 

 responding to the intermesenterial chambers was observed to 

 begin but never proceeded far and no mesenteries were regener- 

 ated (see Fig. 3, Child, '03/7). The fact that tentacles never 

 appear in such cases where mesenteries are absent indicates that 

 their regeneration is dependent in some manner upon the presence 

 of the mesenteries. In pieces where regeneration of the mesen- 

 teries occurs, regeneration of the tentacles never precedes or coin- 

 cides in time with the appearance of mesenteries, but always fol- 

 lows. Various observations of others and my own upon other 

 species of actinozoa indicate that this rule holds good not only 

 for regeneration but for the normal development and for addition 

 of new tentacles in adults. The new mesentery appears first, 

 then the tentacle. 



The interpretation of this "correlation" is not difficult if we 

 accept the point of view suggested above. According to this it 

 is evident that the mesenteries serve to localize the currents pro- 

 ceeding orally along the body-wall, /. e., the current of one inter- 

 mesenterial chamber is separated by the bounding mesenteries 

 from that in the adjacent chamber. If the mesenteries were not 

 present the current would strike the oral margin in a continuous 

 circle and if it produced any effect at all would cause the out- 

 growth of the whole margin. 1 



The outgrowth of the whole margin, /. i\, the spreading of the 

 disc, occurs to a certain extent in every case of regeneration and 



1 It is conceivable that in such a case the surface tension of the outgrowing margins 

 might operate in such manner as to cause it to break up into a number of radiating 

 masses of certain size. It is not impossible that the tentacles of certain ccelenterates 

 are formed in some such manner whether the stimulus to growth be water-pressure or 

 some other. This process might be compared to the breaking up of the margins of a 

 drop of fluid into radiating cylindrical masses, which occurs when it is allowed to 

 drop with force upon a smooth hard surface and " splashes." In this case we have a 

 continuous cause with discontinuous effect. The close relation between the number 

 of tentacles and the size, /. e., the circumference, in such forms as Hydra, indicates the 

 possibility of an explanation of this kind. 



