268 BRADLEY M. PATTEN 



It is clear that no reaction such as orientation can result 

 from a stimulus which does not first induce activity on the 

 part of the organism. The kinetic energy liberated by stimula- 

 tion must be regarded as the basis of any movement due to the 

 influence of the stimulus, however highly modified or definitely 

 restricted that movement may be. There is no reason to think 

 that stimulation itself, or the conditions capable of producing 

 stimulation, differ whether the motor responses initiated are 

 tropic or simply kinetic. The conditions which determine the 

 directive or non-directive character of the response are to be 

 sought rather in the distribution and intensity of the stimulus 

 actually effective on the receptors, and the existence within the 

 organism of transmission paths which limit or direct the kinetic 

 response. 



Any analysis of the mechanism of orientation should, there- 

 fore, be based on a consideration of the kinetic response to stimu- 

 lation. From this point only, is it possible to proceed logically 

 to a consideration of the factors which so determine the direc- 

 tion of expression, and intensity of the activity set up by stimu- 

 lation, that locomotion in a definite direction is established. 



Mastigoproctus, at least while confined in the laboratory, 

 exhibits a strong tendency to remain quiet unless stimulated in 

 some way. Illumination above 0.16 candle meters intensity 

 acts as a stimulus inducing locomotion. If animals which are at 

 rest are subjected to illumination from above they begin to move 

 about aimlessly. Activity does not cease immediately after the 

 change in illumination necessarily involved in starting the ex- 

 periment. On the contrary locomotion persists for long periods 

 of time.i When the light is shut off, locomotion ceases. During 

 this procedure the animal being uniformly illuminated from 

 above, there are no appreciable changes in the intensity of the 

 light operative on the photoreceptors. The conclusion is clear, 



^ In many cases already recorded acclimatization to steady illumination is 

 known to result, after varying periods of time, in the cessation of stimulation. 

 The scorpion is no exception. Cessation of activity due to acclimatization bears 

 in no way on the point at issue. The process is one involving so long a time that 

 it can play no ai)i)reciable j)art in an orientation which is immediate. 



