Jknnings, BcJuxvior of ParaiiiCiiuiH. 443 



nese ink) mucli preferable to that of carmine or indigo. The 

 ink is procured in sticks and rubbed up with vvati-r in the usual 

 way. 



I. TnK Action Svsti:m. 



By the behavior of an organism we mean essentially the 

 regulation, by means of movement, of its relations to environ- 

 mental conditions. The characteristic complex of movements 

 by which the relations of Paramecium to its environment are 

 determined may be called the "action system" of the organism. 

 Most animals have certain peculiar methods of action, depend 

 ing largely upon their structure — upon what vON Uexkull 

 (1903, p. 269) calls the "biologische Hauplan" — by which most 

 of their behavior is brought about. These characteristic ways 

 of acting are usually few in number and form a unified system, 

 providing a definite reaction combination for any stimulus. The 

 reaction systems of different animals vary as much as do 

 their structures. Thus many different agents acting on a given 

 animal may produce the same set of movements, while on the 

 other hand the same agent acting 011 organisms of dilTerent 

 ■"action systems" produces in each case different movements. 

 The method of reaction then depends as much on the action 

 system of the organism in cjuestion, as upon the physical or 

 chemical action of the stimulus. The usual relation between 

 the two factors may be expressed as follows : The action sys- 

 tem supplies a limited number of methods of action, the char- 

 acter of the stimulus (including its localization) determines 

 which of these methods shall be set in operation. 



In dealing with the action system of Paramecium, we have 

 to consider, first, the usual movements and the environmental 

 relations which they induce ; second, the typical modifications 

 of these movements (the reaction types), under the influence of 

 stimulation. 



I.. The Usual Movcnicitts ; Spiral SiK.nmniing. — As is well 

 known, Paramecium continually swerves toward the aboral side 

 and revolves on its long axis as it swims through the water, so 

 that its course is a spiral one (Fig. 3). The revolution, so far 



