20 



Charles Zeleny. 



in shape but the ends of each are curved inward. This shape 

 evidently has some connection with the proper collection of the 

 food particles carried downward by the cilia. (See Fig. 5B, c.) 

 The number of the branchiae increases with the age of the animal 

 and in fully grown individuals there are about fourteen on each 

 side. 



F 



Fig. 5. 

 Hydroides dianthus. A — Dorsal vie\v of right-handed specimen, showing relations of parts. Ends 

 of branchiffi and functional operculum not given ( X 6). B, C — Diagram of anterior surface of head of 

 left-handed and right-handed specimens ( X 6). D — Branchia viewed from inner surface ( X 25). 

 E — Rudimentary operculum ( X •;o). F — Functional operculum ( X 30). 



