Factors in Regeneration 33 1 



ends of all branches, cut at any level, and from the distal ends 

 of pieces from the apical region of the stem. The coenosarc 

 also withdraws, as a rule, from the distal ends of small pieces 

 from any part of the colony. In the diagram of a large stem 

 a represents the oral, / the basal end. We can foretell with a 

 fair degree of accuracy whether polyps will be formed at one or 

 the other ends of pieces and the relative number regenerated at 

 each end, provided we know the level at which the cuts were 

 made. In pieces b c, no hydranths will appear at b, many at c; 

 in pieces / h or g i more hydranths will appear at / and g, 

 respectively, than at h and /. In region a f the nearer to a the 

 oral end of a piece lies the fewer the oral polyps; in region / / the 

 nearer to / the basal end of a piece lies the fewer the basal 

 hydranths regenerated. 



The recession of the ccenosarc from the distal end may extend 

 only one internode or half a dozen or more, and the hollow peri- 

 sarc thus produced often cracks and breaks off." In small pieces 

 the ccenosarc may move not only toward the basal end but through 

 the basal end entirely free from the perisarc, leaving the empty 

 perisarc behind. Placing inverted stems in sand accelerates the 

 basal movement of the ccenosarc, so that the parts embedded 

 in sand become entirely empty; the ccenosarc is found only in the 

 basal regions surrounded by water. In erect stems under the 

 same conditions the ccenosarc withdraws somewhat from the dis- 

 tal end while at the basal end it either (i) does not withdraw at 

 all, in the majority of cases, and in spite of the adverse conditions, 

 (2) or slightly withdraws, (3) or disintegrates, the result of the 

 ravages of large numbers of ciliate protozoa. 



Two counteractmg tendencies may be said to be present at 

 every cut end of a stem or branch, the resultant of which deter- 

 mines whether a hydranth will or will not be regenerated, and 

 whether regeneration will or will not be retarded; first, the 

 movements of the coenosarc from the distal cut ends already 

 described, second — and I believe second in point of time — the 

 regeneration of new tissue, which is negatively geotropic and, 



"Gast and Godlewski, loc. cit. 



