150 BEHAVIOR OF THE LOWER ORGANISMS 



seems to be the result of a slight activity of the cilia, tending to cause 

 movement upward, combined with the downward pull of the thread 

 at the posterior end. Jensen found that Colpoda cucullus, Colpidium 

 col pod a, Ophryoglena flava, and Coleps hirtus showed no clear reac- 

 tion to gravity. 



There is reason to suppose that reaction to gravity, where it occurs, 

 is brought about in the same manner as in Paramecium. The details 

 given in the account of Paramecium therefore need not be repeated here. 



As a general rule the reaction to gravity is easily masked by reactions 

 to other stimuli. It is shown in a marked way only when other effective 

 stimuli are largely absent, and in cases of conflict with other reactions, 

 it is usually the reaction to gravity that gives way. In some cases the 

 action of other agents causes the reaction to gravity to become reversed, 

 just as in Paramecium. Massart (1891 a) finds that this effect is pro- 

 duced in Chromulina by lowering the temperature to 5-7 degrees C. 



A number of infusoria are known to react to centrifugal force in the 

 same way as to gravity. They swim in the opposite direction from 

 that in which the centrifugal force tends to carry them, just as Parame- 

 cium does. It is probable that in all cases centrifugal force could be 

 substituted for gravity without essential alteration of the reactions. 

 Schwarz (1884) found that Euglena and Chlamydomonas react to cen- 

 trifugal force when it is equal to about -|- the force of gravity, and con- 

 tinues the reaction till the centrifugal force is about 8^- times gravity. 

 Above this they are passively carried in the direction of action of the 

 centrifugal force. 



LITERATURE VIII 

 Behavior of Infusoria in General 



A. Reactions to light: Jennings. 1904 a\ Strasburger. 1878; Engelmann, 

 1882; Mast, 1906; Famintzin, 1867; Hertel, 1904; Holt and Lee, 1901 ; 

 Holmes, 1903; Oltmanns, 1892. 



B. Reactions to gravity : Jensen, 1893; Massart, i 891 a ; Schwarz, 1884. 



