140 Journal of Comparative Neurology and Psychology. 



embrace all reactions due to a change in the intensity of action 

 of a stimulating agent. Gakrev's use of the term kinesis seems 

 a little uncertain, since he seems in one place (p. 292) inclined 

 to consider it equivalent to Davenport's -pathy. thus including 

 directed reactions to changes in intensity, while in general he 

 seems to limit it to increase or decrease of activity, in the sense 

 in which it was employed by Engelmann and Rothert. Gar- 

 REY uses the term in contradistinction to tropism, which is de- 

 fined in accordance with the well known views of Loeb. 



Perms ending in -metry have been contrasted with taxis, 

 especially by Strasburger' and Oltmanns,^ to distinguish those 

 features of the reactions that are determined by differences in 

 the intensity of the stimulating agent. Photometry is employ- 

 ed by Strasburger to signify especially the phenomenon that 

 some organisms move toward tiie source of light in a certain 

 intensity of illumination, while they m^ove away from it at a 

 higher intensity. By Oltmanns photometry is used of any re- 

 actions due to differences in the intensity of light ; "movements 

 produced by light of different intensity could fittingly receive 

 the name photometric movement" (Oltmanns, /. c, p. 190). 



Thus we find various attempts to distinguish by one criter- 

 ion or another two great classes of reactions. On the one hand 

 we have apobatic taxis (Rothert), phobotaxis (Pfeffer), pho- 

 bism (Massart), kinesis (Engelmann, Garry and others), -pathy 

 (Davenport), -metry (Strasburger and Oltmanns); in these 

 orientation is not a marked feature. On the other hand we 

 have tropism or taxis proper (Loeb, Davenport, Massart, 

 Verworn and others), strophic taxis (Rothert), topotaxis 

 (Pfeffer); in these orientation is a marked feature. What is 

 the precise basis for this distinction into two classes? 



In the behavior of infusoria (ciliates and flagellates) it is 

 possible to distinguish clearly the two classes of phenomena on 

 which this distinction is based, and to determine the real nature 

 of the difference.'^ In both classes the cause of reaction is. in 



^Jena. Zeitschr. f. iVaturw., 12. 1878. ''Flora, 75, 1892, p. 183. 

 •'In the effects of the electric current the usual reaction method is in the Ci- 

 liata interfered with by the forced cathodic reversal of the cilia, — a factor not par- 



