Jennings, Behavior of Paramechim. 445 



But the monocular is deceptive on that point. An investigator 

 who was certain that in a particular culture many of the individ- 

 uals were thus "reversed" made at my request a careful exam- 

 ination of a large number, after killing them with an excellent 

 fixing solution. Not a single reversed specimen was found. If 

 such exist, they are certainly extremely rare. 



The obliquity of the oral groove — from right behind to 

 left in front — appears to be the opposite of that which would 

 assist the revolution over to the left. If the groove should act 

 like the groove of a screw, moving along a solid ridge, the ani- 

 mal would revolve over to the right instead of over to the left. 

 It is of course known that the revolution on the long axis is in- 

 dependent of the groove, since when the animal is cut in two 

 in such a way that no part of the groove remains on the pos- 

 terior half, this half nevertheless continues to revolve on its 

 long axis when moving forward (Jennings and Jamieson, 1902). 

 The significance of the direction of the oral groove is probably 

 to be sought in its relation to the stream of water which it leads 

 to the mouth. 



The width of the spiral path of Paramecium varies much. 

 The spiral is narrowest when the animal is progressing most 

 rapidly, through water which presents no stimuli ; its width is 

 then equal to about one-half the length of the animal. Usually 

 the spiral is wider than this ; the length of the animal is per- 

 haps a fair measure of the average width. In many cases, as 

 after stimulation, the width is much greater ; it may be several 

 times the length of the animal. Paramecium as a rule makes 

 one turn of the spiral, reaching a corresponding phase or posi- 

 tion, in about four times its length ; but this relation is also 

 variable. 



The spiral motion is compounded of three factors : (i) 

 the forward movement ; (2) the swerving toward the aboral 

 side ; (3) the revolution on the long axis. Each of these fac- 

 tors depends on certain peculiarities in the stroke of the cilia. 

 The forward motion is due of course to the fact that the cilia 

 strike in a general way backward. The revolution on the long 

 axis is due to the fact that the stroke is not directly backward, 



