56 



Charles Zeleny. 



operated functional operculum has fallen off the rudimentary 

 operculum has started to enlarge and processes appear at its distal 

 end. Gradually the structure increases in size and assumes 



^ 



a 



B 



a 



C 



a 



c 



d 



Fig. 19. 



Hydroides dianthus. A, a-/ — Stages in the development of a rudimentary operculum from the stump 

 of an old functional one ( X 54). B, a-e — Stages in the regeneration of a rudimentary operculum 

 after a cut at the region indicated by the double-headed arrow ( X 54). C, a-d — Stages in the trans- 

 formation of the old rudimentary operculum into the new functional after removal of the old functional 

 operculum. The final condition of the functional operculum is shown in Fig. 5F. 



