XVIII INSTINCTS AND TROPISMS 343 



duct, even were it capable of so doing. Such behavior 

 affords a typical illustration of instinct ; and throughout the 

 animal kingdom it is instinct which is the dominant element 

 in conduct. 



The behavior of the frog is almost entirely made up of 

 instinctive actions. Nature has equipped this animal with 

 the means of getting through the world without relying, to 

 any great extent, upon the lessons of experience. The frog 

 has intelligence of a rudimentary sort, to be sure, but it 

 plays a very subordinate role in shaping the creature's con- 

 duct. It is truly a marvelous thing that an animal should 

 be endowed with the power of successfully adapting its con- 

 duct to a complex environment without any perception of 

 the consequences of its actions. How can the existence 

 of such a power be explained, or brought into relation with 

 our knowledge of the other features of the animal's life? 



It was formerly customary to regard instinct as a property 

 sui generis, something having no necessary affiliation with the 

 other functions of the organisms, a sort of power with which 

 animals are mysteriously endowed for their guidance. 



It is but another illustration of the effect of increasing 

 knowledge in bringing different fields of biological inquiry 

 into closer and more organic connection that the instinctive 

 behavior of animals is now shown to be more intimately 

 connected with their structure and physiological activities. 

 Instinct is but a phase of the general life process, exhibiting 

 the same purposiveness that is shown in the activities of the 

 heart or alimentary canal. All parts of the body are con- 

 tinually responding to stimuli in ways that are beneficial to 

 the organism. When the stomach pours out its secretion 

 and begins its peristaltic movements upon the receipt of 

 food and allows the material when digested to escape 

 through the pylorus, it is performing actions which we do 



