FORM REGULATION IN CERIANTHUS. 



II. THE EFFECT OF POSITION, SIZE AND OTHER FACTORS UPON 



REGENERATION. 



C. M. CHILD. 



In the preceding paper (BiOL. BULL., Vol. V., No. 5, 1903), 

 the course of regeneration in cylindrical pieces from the middle 

 region of the body was described, since such pieces afford a typ- 

 ical result and serve as a basis for comparative study. It is de- 

 sired in the present paper to call attention to certain conditions 

 which influence the result, either as regards time or quantity. 



The principal features in the regeneration of Cerianthns may 

 be reviewed as follows : the collapse of the piece after section 

 and the infolding of the ends ; the closure of the ends by new 

 tissue and the gradual distension of the piece and the increase in 

 the area of the new tissue at the ends in consequence of the 

 accumulation of water in the enteron, probably by diffusion 

 through the body-\vall ; the reduction and disappearance of the 

 muscular layer and pigment at both ends ; the regeneration of 

 mesenteries ; the outgrowth from the tentacular ridge of a mar- 

 ginal tentacle over each intermesenterial chamber ; the formation 

 of the mouth in the directive radius ; the appearance of the 

 labial tentacles in a circle upon the disc ; the outgrowth of new 

 tissue at the aboral end of the piece. 



Since each of these processes is gradual it is impossible to de- 

 termine with exactness the time of its beginning ; moreover, the 

 various processes overlap and are connected in such a manner 

 that it is difficult to separate distinct stages except arbitrarily. 

 For these reasons the comparison of different pieces with a view to 

 determining the conditions which effect regeneration can best be 

 accomplished by the examination of these pieces at stated times, 

 rather than by noting the time at which a given piece arrives at 

 a particular stage. The former method not only allows direct 

 comparison of the pieces, and thus often renders the detection of 

 slight differences less difficult, but it obviates the necessity for 



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