200 DONALD WALTON DAVIS 



DISCUSSION OF REGENERATION IN HEXACTINIANS 



The only previous detailed accounts of radial regeneration of 

 sea-anemones comparable with the foregoing are those of Carl- 

 gren ('04 and '09) and Gary ('11). I shall now review the work 

 of these writers in so far as it bears upon the problems here 

 considered. Carlgren dealt with the regeneration of Sagartia 

 viduata, Metridium dianthus, and Aiptasia diaphana. Of the 

 last-named species only naturally produced basal fragments were 

 studied. In Metridium, the material considered of natural frag- 

 ments, artificial pieces of the same character as those separated 

 naturallj^, and pieces cut from the base of the parent polyp in 

 such a way as to exclude, so far as possible, all tissue of the 

 column and of the mesenteries. I shall refer to these last as 

 'basal pieces.' Of Sagartia viduata, which does not reproduce 

 naturally by asexual methods, artificial fragments of various 

 forms and sizes were used, including some 'basal pieces.' 



Natural fragmentation in Metridium and Aiptasia consists in 

 the separation from the parent polyp of a small portion of the 

 base and adjacent wall of the column with the adhering parts of 

 mesenteries. The fragment thus receives only a very small 

 proportion of the material of the parent polyp. The products of 

 division in S. luciae, while they may be far from equal, are, so 

 to speak, of the same order of magnitude, and each contains 

 some part of the base, column, esophagus, circle of tentacles, 

 and set of mesenteries. 



Resorption of old mesenteries 



In Metridium and S. viduata degeneration of mesenteries is 

 evidently a prominent feature of the process of reconstruction. 

 In these forms, however, degeneration does not commonly go to 

 the extent of eliminating all of the old mesenteries. In Aiptasia, 

 as stated by Andres ('82), rearrangement of mesenteries begins 

 before the separation of the fragment from the parent. Carl- 

 gren believes that degeneration of the mesenteries, also, begins 

 before separation is complete. He leaves in doubt the extent 

 to which degeneration may go, since he was unable to determine 



