442 Journal of ('ompdralivr Neuroloi^y luid Psychology. 



Since Paramecium is usually taken as a t\pe for the study 

 of unicellular animals, it is desirable to have its reactions to 

 stimiiH as fully known as possible. In attempting to put to- 

 gether the results of numerous investigations made during the 

 last fifteen years on the behavior of this animal, 1 have found 

 that there are still a number of reactions which have not been 

 described, or have been described incorrectly, and that certain 

 general relations running through the behavior have never been 

 brought out. The present paper attempts to fill, so far as 

 possible, these gaps in our knowledge, sujjplementing and uni- 

 fying previous accounts of the behavior of Paramecium. The 

 writer tries to point out omissions or errors in his own pre- 

 vious work with the same impartiality as in the works of others. 



The chief subjects dealt with are, in the first ])lace, what 

 we may call the action system of Paramecium ; in the second 

 place, the fundamental character of the stimulations to which the 

 animal resjjonds. In the third place an account is given of cer- 

 tain imperfectly or incorrectly known reactions, with particular 

 reference to their relation to the "action system" of Parame- 

 cium. The chief reactions thus taken up are "rheotaxis," 

 "geotaxis" and "electrotaxis." 



Methods. — A word should be said here as to certain meth- 

 ods of work. Throughout the following paper accounts are 

 given of the direction of the effective beat of the cilia. This 

 was determined in e\'ery case by mingling finely grouml India 

 ink with the water containing the Paramecia, thus observing 

 the direction of the currents caused b\' the cilia. By using 

 such a method one is not reduced to conjecture as to the realh' 

 effective direction of the ciliary beat, as has been the case in 

 certain papers on this subject, but this effective direction is de- 

 termined immediately by observation. 1 have supplemented 

 this method by observing the cilia of animals partly confined in 

 a gelatin solution, in the usual wa)', and of animals partly stu- 

 pefied with chloretone. These methods gave especially got)d 

 results when combined with the use of India ink, to show the 

 currents. Owing to its fineness, blackness, and absolute lack 

 of chemical action, I have fountl the use of India ink (or Chi- 



