8 INTRODUCTION 



in regarding them as unconscious automata and should 

 proceed to cut them up in a ruthless fashion on that as- 

 sumption. It may be, as Norman has attempted to show, 

 that pain sensations in the lower invertebrates are not 

 acute at most, and may be absent entirely, but not much 

 would be lost by giving the animals the benefit of the 

 doubt so far as is consistent with attaining the objects of 

 experimental work. 



The scientific instinct for continuity tempts us to ascribe 

 some form of sentiency to all living forms. Certainly it is 

 not possible to disprove the existence of consciousness of 

 some sort in any organism. In the lowest animals it may 

 be nothing more than a very dull form of sensibility. If we 

 would avoid the assumption of an absolute beginning of 

 consciousness we may hold that something akin to con- 

 sciousness, but very much more primitive than any of the 

 forms of it with which we are acquainted, exists in connec- 

 tion with all inorganic processes. Such a position affords 

 a consistent viewpoint and has been accepted by many as 

 enabling us to conceive the whole process of psychic evolu- 

 tion as one without any breaks or discontinuities anywhere 

 in the series. 



Our task hi the present volume is to sketch briefly the 

 evolution of behavior from its simplest manifestations 

 in the reflex actions of the lowest organisms to its more 

 elaborate expressions in the higher mammals. No attempt 

 has been made to give a survey of behavior in all the groups 

 of the animal kingdom. Beginning with simple reflex action 

 we have described those forms of behavior which are com- 

 monly called tropisms and which are by many regarded as a 

 comparatively direct outcome of reflex irritability. After 

 an account of behavior of 'the lowest members of the ani- 

 mal kingdom we have given a general account of instinct, 



