AMEBOID MOVEMENT 135 



A simple but decisive experiment by Jennings ('06) showed that 

 the revolution and the forward movement of a paramecium is 

 due to the oblique stroke of the cilia, for the severed posterior 

 portion of a paramecium, which is symmetrical, nevertheless still 

 revolves during progression. The question now arises whether 

 this oblique stroke is analyzable into components in another way 

 than by local stimulation ; for example, can one increase or de- 

 crease the amount of revolution faster than the amount of pro- 

 gression? Observation of paramecium and euglena in different 

 temperatures answers this question affirmatively. Organisms 

 from the same culture were subjected to two temperatures, the 

 culture temperature of 21 C. and 8 C. At temperatures lower 

 than 8 C. the paramecia quickly precipitated to the bottom of 

 the dish. 



In 21 C. paramecia revolve once while swimming 5.5 body 

 lengths. 



In 21 C. euglenas revolve once while swimming 4.2 body 

 lengths. 



In 8 C. paramecia revolve once while swimming 3.6 body 

 lengths. 



In 8 C. euglenas revolve once while swimming l /\. to 2 body 

 lengths. 



The effect of decreased temperature is therefore to retard for- 

 ward movement and to increase proportionally the number of 

 spiral turns, for a revolution of the body on the long axis is 

 the equivalent of one turn in the spiral path. It will be recalled 

 that a similar result was obtained with amebas ; in the lower tem- 

 perature the rate of forward movement was reduced and the ten- 

 dency to deepen the waves increased. In both these classes of 

 organisms, differences in temperature enable one to separate the 

 forward movement component from the spiral component, in the 

 same way and in general to the same extent. 



In clear water of optimum temperature or somewhere near it, 

 paramecia and euglena (Euglena gracilis, which does not readily 

 react to light) often swim for long stretches without change of 

 direction. When the temperature is lowered, however, the 

 stretches of straight paths become much shorter. In a tempera- 

 ture of 8 C. changes of direction become very frequent. In 



