Compensatory Regulation. 



49 



Fig. 17. 

 A — H. dianthus. Age, 34 days. Primary rudimentary operculum, right side ( X 50). B — H. 

 pectinata. Age, 45 days. Dorsal view. Functional operculum of Serpula type on left. Rudimentary 

 operculum on right. Pinnules are shown in only one branchia, the other branchiae being essentially 

 similar to this one. C — Tube of H. pectinata. Age, 45 days ( X 6). D — Hydroides uncinata. Age, 

 46 days. Ventral view. Shows Serpula type of functional operculum on left side and rudimentary 

 operculum on right. E — Diagram of cross-section of a branchia of H. uncinata showing method of 

 attachment of pinnules. F — H. uncinata. Age, 179 days or nearly six months. Original or Primary 

 functional operculum as appearing after it has dropped off. 



