Plate XVIII. Metachronal waves and ciliary beating of 

 Opalina. 



{a) Dark-ground photographs of several animals to show 

 examples of metachronal wave patterns. The two animals on 

 the right are turning; in all cases the waves are moving approxi- 

 mately from the top of the plate to the bottom. All prints at 

 about >: 40. 



{b) A series of cine photographs of a group of cilia of Opalina. 

 The metachronal waves move from left to right along the row 

 of cilia that are in focus. (Cf. Figs. 39 and 47.) Interval 

 between exposures h sec. X 300. 



