FORM-REGULATION IN CERIANTHUS. 199 



I have at present no further evidence upon this point, as my 

 attention was not directed to it early enough. I am inclined to 

 believe, however, that there may be a slight acceleration here, 

 provided the inrolling of the margins is not so irregular that 

 closure is delayed, as is frequently the case in oblique pieces. 



Leaving this point for future experiments to decide, the retar- 

 dation of regeneration on the lower portions of the oblique discs 

 is sufficiently evident and requires explanation. In the course of 

 my experiments several other pieces were cut obliquely and 

 always with the same result, viz., appearance of the tentacles 

 first on the uppermost portion of the disc and from this region 

 on each side in succession toward the lowest portion. The ten- 

 tacles on the lowest portion always appeared later than in trans- 

 versely cut pieces at the same level. 



As in the case of typical regeneration from a transverse cut sur- 

 face, the presence or absence of a cut aboral end and the plane of 

 the cut if present do not affect the oral regeneration except in so 

 far as irregular or delayed closure of the aboral end may delay 

 distension. 



It is difficult to conceive any reason for this retardation of re- 

 generation in the organic relations of parts of the oblique piece. 

 Why should there be any difference between a portion of an 

 oblique disc and a transverse disc at the same level of the body ? 

 Yet tentacle-regeneration on the former requires about twice as 

 much time as on the latter. 



The only plausible reason for this difference that has occurred 

 to me thus far is the difference in the relation between the inrolled 

 margin and the circulatory currents in the oblique and transverse 

 pieces. It is evident, I think, that as soon as the oblique piece 

 becomes closed by new tissue, and distension and stretching of 

 the body-wall occurs, the chief tension upon the inrolled margins 

 will coincide in direction with the plane of the disc. Thus on the 

 lowest portion of the oblique disc the direction of tension will be 

 obliquely upward and on the highest portion it will be obliquely 

 downward. The result is that at the lowest portion of the mar- 

 gin the disc forms an obtuse angle with the body-wall, while on 

 the opposite side the angle is acute ; between these points the 

 angle varies between these limits. Examination of the specimens 



