THE BEHAVIOR OF INFUSORIA; PARAMECIUM 79 



But in the reactions to water currents, gravity and centrifugal force, 

 it is a certain position of the body that results in stimulation ; displace- 

 ment of the cilia, or of certain internal constituents, occur in certain 

 positions of the body, causing disturbances to which the animal reacts, 

 as usual, by the avoiding reaction. This reaction consists in successively 

 "trying," not only different directions of locomotion, but also different 

 positions of the body axis, as a glance at Figs. 37-39 will show. As soon 

 therefore as a position is reached in which the disturbance causing the 

 reaction no longer exists, the reaction of course stops ; the animal there- 

 fore retains this axial position. 1 



A comparison of the reactions to these two sets of agents brings out 

 strongly the general adaptiveness and effectiveness of the reaction 

 method of the infusorian. The avoiding reaction is of such a charac- 

 ter as to bring about in a systematic way (1) different directions of 

 movement; (2) different axial positions; (3) different environmental 

 conditions (of temperature, chemicals, etc.). If any one of these puts 

 an end to the disturbance which caused stimulation, the reaction of 

 course stops at that point, and the animal retains the direction of move- 

 ment, axial orientation, or environmental condition thus reached. If a 

 certain axial orientation must be reached before the stimulating dis- 

 turbance ceases, then the result of the reaction will be to produce this 

 orientation. If the disturbance ceases before a common orientation of 

 all the individuals is reached, then no common orientation will occur. 

 In other words, the method of reaction is such as to bring about any 

 condition whatsoever that is required in order to put an end to stimula- 

 tion, — provided of course that this condition is attainable. It will 

 therefore produce in some cases a certain direction of movement, in other 

 cases a certain axial orientation, in other cases the retention of a certain 

 environmental condition, just as circumstances may require. 



LITERATURE IV 



A. Reactions to contact with solids : Putter, 1900; Jennings, 1897, 1899. 



B. Reactions to chemicals : Jennings, 1897, 1899 c; Greeley, 1904; Barratt, 

 1905. 



C. Reactions to heat and cold : Jennings, 1904; Mendelssohn, 1895, 1902, 

 1902 a, 1902 b. 



D. Reactions to light : Hertel, 1904. 



E. Reactions to water currents : Jennings, 1904//: Lyon, 1904, 1905. 



F. Reactions to gravity and centrifugal force : Lyon, 1905 ; Jensen, 1893 ; Jen- 

 nings, 1904//; Sosnowski, 1899; Moore, 1903. 



1 It is worthy of note that the position of orientation is not one in which a median 

 plane of symmetry takes up a definite position with reference to the external agent, as is 

 sometimes set forth. The infusorian when oriented continues to revolve on its long axis, 

 so that no more can be maintained than that the longitudinal axis (in reality the axis of 

 the spiral path) is in line with the orienting force. 



