262 THE AMERICAN. NATURALIST. [VoL. XXXIV. 
acids, described on pp. 314, 315, of the Second of my Studies.} 
This possibility is not discussed by Garrey, apparently because 
of a preconceived view that chemotropism must take place ac- 
cording to Professor Loeb's generalization above quoted. He 
says: *Jennings's motor reaction cannot account for orienta- 
and, therefore, that it has nothing to do with tropisms. 
This unsupported sweeping denial seems a peculiar way of 
meeting such a detailed account of the production of orientation 
through the motor reaction as I have given for the thermotaxis 
of Paramecium on pp. 334-336 of the Second of my Studies. 
The general proposition that a motor reaction cannot cause 
orientation seems still more remarkable. Consider an organ- 
ism, as in the figure, lying obliquely to the line of action of 
the incoming stimulus, which is indicated by the four straight 
arrows. Its position is at first a-a. After the stimulus has 
acted for a.time, the organism is found to be oriented as shown 
at 6-8, with its longitudinal axis in the direction of the lines of 
force. Now, how can this orientation possibly take place except 
through a motor reaction? The animal has certainly moved 
under the influence of the stimulus from the position a-a to the 
position 4-4, and such a movement under the influence of a 
stimulus is what is commonly known as a motor reaction.? 
1 Amer. Journ. v Pio. vol. ii, pp. 311 -341. 
2 Garrey's attempt to attribute to me the absurd idea that the principle of. a 
motor reaction is new (/oc. ¿ity p. 313, note), is perhaps‘ unworthy of mention. 
The comparison of the motor reaction of. Paramecium with that of a muscle, 
