1910] Torrey: Regeneration of Hydranth and Holdfast. i* 1 ! » 



The hydranth is in every way normal, and the entire individual 

 is essentially identical with a larva developed from the egg. 

 Three proximal and three distal tentacles appeared on this 

 individual. 



Regeneration in the proximal portion of a larva with seven 

 proximal and four distal tentacles, sectioned just below the edge 

 of the perisarc led. in one week, to a normally proportioned 

 larva with the original number of tentacles. 



These cases will suffice to call attention to the ease with which 

 larval stems regress to an earlier, non-tentaeled stage, from 

 which differentiation proceeds as in the original development. 

 Just as the hydranth and stem regions are first defined in the 

 larva by the slight differentiation of functional epithelial cells 

 in situ, so the transformation of the distal end of a sectioned 

 stem involves similar slight changes. The differences between 

 the tissues of stem and hydranth are so small at this time as to 

 facilitate the process. 



III. CONclcs I ox. 



The plasticity which is so conspicuous a characteristic of the 

 normal development of Corymorpha is also a striking feature of 

 the regenerative development. The latter approximates the 

 former, in fact, at every possible point, varying from il in detail 

 only with the advancing differentiation of the regenerating 



pi' • Tissues in larval stages of differentiation will produce 



larval structures in the larval way, whether in regeneration or 

 normal development. Adult structures, arising on an adult stem, 

 vary from this early normal type in the details of their develop- 

 ment. The rootlets of the holdfast show the least difference in 

 this respect, developing essentially as in the embryo throughout 

 the life of the polyp. Yet they arise from larger fundaments 

 involving larger numbers of cells. This is true of the tentacles 

 also. Their development involves, further, a process more com- 

 plicated in its details, evidently connected with the structure of 

 the fully developed organ. Where the frustular axis is never 

 composed of more than a single row of endodermic cells, whether 

 in larva or adult, the axis of the tentacle is made up of rows of 

 endodermic cells, especially numerous at the base. While, then. 



