ITI 

 ON INSTINCT AND WILL IN ANIMALS 1 



1. IN the biological literature one still finds authors who 

 treat the "instinct 1 ' or the "will" of animals as a circum- 

 stance which determines motions, so that the scientist who 

 enters the region of animated nature encounters an entirely 

 nr\\- category of causes, such as are said continually to pro- 

 duce before our eyes great effects, without it being possible- 

 for an engineer ever to make use of these causes in the physi- 

 cal world. "Instinct" and "will" in animals, as causes 

 which determine movements, stand upon the same plane as 

 the supernatural powers of theologians, which are also said 

 to determine motions, but upon which an engineer could not 

 well rely. 



My investigations on the heliotropism of animals led me 

 to analyze in a few cases the conditions which determine the 

 apparently accidental direction of animal movements which, 

 according to traditional notions, are called voluntary or 

 instinctive. Wherever I have thus far investigated the 

 cause of such "voluntary" or "instinctive" movements in 

 animals, I have without exception discovered such circum- 

 stances at work as are known in inanimate nature as deter- 

 mining movements. By the help of these causes it is pos- 

 sible to control the "voluntary" movements of a living ani- 

 mal just as securely and unequivocally as the engineer has 

 been able to control the movements in inanimate nature. 

 What /m.s been token for 11m effect of'-iciU" or "instinct" 

 is in realilij Ilic effect of U</ht, of yrtu ////, of friction, of 

 chenn'col forces, etc. The following may be added by way 

 of fuller explanation: 



lPflatjersAr<.-ht'i; V.,1. XLVII (1S9J>. p. 107. 



107 



