114 THE BEHAVIOR OF LOWER ORGANISMS. 



conditions form a continuum. We can, by taking sections, as it were, 

 at different intervals, distinguish at least six actually different condi- 

 tions ; but doubtless there exists every possible gradation from one to 

 another, so that still other actually different conditions could be distin- 

 guished if we had criteria for separating them. By careful analytical 

 experiments the number of different physiological conditions clearly 

 recognizable could doubtless be increased. 



In other unicellular organisms doubtless a condition of affairs may 

 be found similar to that set forth above for Stentor. Hodge & Aikins 

 (1895) showed that the reactions of Vorticella vary with its physio- 

 logical condition. In the same paper (Jennings, 1902, a] in which 

 the behavior of Stentor was described, I have shown that in various 

 other fixed infusoria (Carchesium, Epistylis, etc.) the behavior like- 

 wise depends upon physiological states of the organism. In the 

 free-swimming infusoria this has not been shown to be true, at least to 

 any such extent. There may two grounds for this. Firstly, it is proba- 

 ble that in the free-swimming infusoria the behavior is actually less 

 varied than in the fixed species. A single motor reaction usually 

 removes them from the action of the stimulus causing it, so that there 

 is no reason for a recourse to other methods of reaction, as occurs in 

 Stentor. Secondly, in the free-swimming infusoria it is difficult, almost 

 impossible, to observe continuously the reactions of a given single 

 individual. This difficulty could doubtless be met by proper methods 

 of experimentation, and if this were done it can hardly be doubted that 

 a dependence of the reactions on the physiological states of the organism 

 would be found here also. Indeed, we have indirect evidence that this 

 is true in the case of Paramecium, in work already published. Thus, 

 in one of my earlier papers (1899, 0, p. 374) I called attention to the 

 fact that Paramecia from different cultures often vary exceedingly in 

 their reaction to a given solution of a chemical. Still more pertinent 

 to the point under consideration is the fact, described in the first of my 

 studies (Jennings, 1897), as well as in the recent paper of Putter (1900), 

 of the great difference in the reaction of Paramecia and other fixed 

 infusoria when in contact with a solid, as contrasted with their reaction 

 when not thus in contact. As this, however, may be interpreted as an 

 interference of two stimuli, a discussion of the point is reserved until 

 later. A study of individual specimens of some of the larger Hypo- 

 tricha, such as Stylonychia, from the point of view of changes in reaction 

 methods with changes in physiological condition, would doubtless bring 

 forth interesting results. 



Even in the lower unicellular organisms, the Rhizopoda, similar 

 dependence of the method of reaction on the physiological state of 

 the organism is known to exist. Thus Rhumbler (1898, p. 241) has 



