Jennings, Behavior of Paramecium. 455 



ever, the longitudinal motion may be either forward, or zero, 

 or backward. 



As our analysis thus far shows, it is quite inadequate to 

 conceive the cilia as having merely forward and backward strokes 

 — "expansive" and "contractile" phases. The effective stroke 

 may be nearly straight backward or forward ; or obliquely back- 

 ward or forward, with various grades of obliqueness ; or 

 transverse. Furthermore, the cilia of different parts of 

 the body may vary independently in their effective stroke. 

 Thus, we have above distinguished the following conditions : 



1. All the cilia strike almost directly backward (forward 



course. Fig. 3). 



2. All the cilia strike almost directly forward (backward 



course, Fig. 4). 



3. All the cilia strike obliquel)- backward and to the 



right, save the oral cilia, which strike nearly di- 

 rectly backward (forward course, with much 

 swerving toward aboral side). 



4. All the cilia strike obliquely forward and to the right, 



save the oral cilia, which strike nearly directly 

 forward (backward course with much swerving). 



5. All the cilia strike transversely to the right (rotation 



on the long axis, without progression or retro- 

 gression.) 

 ^ 6. The cilia of the right side strike obliquely to the 

 right and backward ; the cilia of the left side 

 strike obliquely to the left and backward (for- 

 ward course, swerving to the aboral side, with- 

 out rotation). 



7. The cilia of the right side strike obliquely to the 



right and forward ; the cilia of the the left side 

 strike obliquely to the left and forward (backward 

 course, swerving to the aboral side). 



8. All cilia strike obliquely forward, save those in the 



oral groove, which strike backward (backward 

 course after a weak stimulus, or after the effect 

 of a strong stimulus has nearly expired. Fig. 5). 



