2OO C. M. CHILD. 



shows this condition very clearly. At the uppermost portion of 

 the disc the body-wall bends over sharply, almost as if actually 

 folded, while the lower margin of the disc is rounded (Figs. 3 and 

 4) and the angle is much less. 



It is evident that circulatory currents passing orally along the 

 inner surface of the body-wall will exert much less pressure on 

 the lower side than on the upper side, since the obtuse angle 

 between disc and body -wall at the lower margin deflects them and 

 permits escape toward the central portions of the body, while at 

 the upper portion of the margin the currents strike an acute 

 angle. On intermediate portions of the disc the angle, and con- 

 sequently the pressure exerted, vary with the position from the 

 maximum at the upper margins to the minimum at the lower 

 margin. It is clear, moreover, that the angle between body-wall 

 and disc at the lowest part of the margin of the oblique disc is 

 greater than that between the body-wall and a transverse disc, 

 while at the upper margin it is less. Half way between the upper 

 and lower oblique margins it is the same as in the transverse disc. 



If there is any relation between the circulatory currents and 

 tentacle-regeneration we might expect acceleration of regenera- 

 tion at the upper margin and retardation at the lower margin 

 of the oblique disc. The retardation of regeneration is very 

 evident, but as regards acceleration the data are insufficient to 

 permit definite conclusions, though there are indications of a slight 

 acceleration. In any case we could not expect the acceleration 

 to be as great as the retardation since in ordinary cases of regen- 

 eration the inrolled margin forms a more or less acute angle with 

 the body-wall and a difference in the size of this angle would 

 make little difference in the pressure so long as the angle remains 

 acute. As soon as the angle becomes obtuse however, the pres- 

 sure must be reduced and as the angle increases the pressure 

 becomes less. 



In this, as in other cases, the regeneration of the labial ten- 

 tacles proceeds in the same manner and sequence as that of the 

 marginal tentacles, though much more slowly. As has already 

 been mentioned, however, I do not know whether there is any 

 localization of pressure in the regions where these tentacles 

 appear. 



