358 University of California Publications. [Zoology 



would exhibit, were it watched from above. The movement may 

 be defined as follows : down, right, up, left, and so on. This 

 constant turning causes the animal to continually change its 

 direction so that its course continues in a fairly straight line. 

 As Jennings ('99) has pointed out, the real significance of this 

 spiral swimming is that it keeps the animals moving in a straight 

 line when the asynnnetry of the body would tend to make it move 

 otherwise. 



In CondyJostoma this movement is directly correlated with 

 the structure of the animal. Starting with dorsal side upper- 

 most, movement forward causes a turning to the left, because of 

 the bend in the posterior end to the left and also downward be- 

 cause of the ventral trend of tip. The combination of these 

 movements tends to rotate the animal on its long axis, so that 

 when the extreme downward position is reached the animal has 

 its ventral surface uppermost. In this position the curvature of 

 the posterior tip is to the right and up, which causes the body to 

 turn to the right and up. The body continues to rotate until it 

 is again dorsal side uppermost. 



In Paramaecium, there are three possible factoi-s that deter- 

 mine this spiral movement: (1) The oblicpie stroke of the cilia, 

 (2) the oblique position of the peristome, (3) the asjanmetrical 

 form of the body (Jennings '99). These factors are also appli- 

 cable to Condylostoma. Concerning the first, the oblique stroke 

 of the cilia, it is very possible that such action could produce 

 the movement. The cilia are placed in straight roAvs which run 

 lengthwise of the animal and not obliquely around it when the 

 animal is not swimming. When the animal is swimming, how- 

 ever, the decurved nature of the posterior end causes the rows of 

 cilia to become somewhat oblique and so would tend to rotate the 

 animal. The second factor, the oblique position of the peristome, 

 is not operative in this species, for the animal moves in a direc- 

 tion directly opposite to that which the oblique position of the 

 peristome would bring about. Whether the third of these fac- 

 tors, the asymmetrical form of the body, has any weight depends 

 on whether the form of the body is a result of the motion or not. 

 That it is not the result of the motion is seen upon observing the 

 shape of the body when the animal is gliding or when it is lying 

 close to the substratum. 



