34 The Structure and Special Physiology of Insects 



elaborateness of many insect instincts, such as those of the ants, wasps, and 

 bees, to choose examples at once familiar and extreme in their complexity, 

 makes it very difficult to analyze the trains of reactions into individual ones, 

 and to determine, if it is indeed at all determinable, the particular stimuli 

 which act as the springs for these various reactions. The attitude of the 

 modern biologist in this matter would be to keep first in mind the theory 

 of reflexes, to look keenly for physico-chemical explanations of the reac- 

 tions, and only when forced from this position by the impossibility of find- 

 ing mechanical explanations for the phenomena to recognize those com- 

 plex reflexes which we call instincts, and finally those acts which we call 

 intelligent, or reasonable, and which are possible only to the possessors of 

 associative memory. The investigations, mostly recent, which have been 

 directed toward a determination of the immediate springs or stimuli of 

 insect reactions indicate clearly that many of these responses, even some 

 which were formerly looked on as surely indicative of considerable intelli- 

 gence on the part of their j)crformers, are explicable as rigid reflex (mechan- 

 ical) reactions to light, gravity, the pro.ximity of substances of certain 

 chemical composition, contact with sohd bodies, etc. On the other hand 

 the position of the extreme upholders (Bethe, UexkuU, and others) of the 

 purely reflex explanation of all insect behavior will certainly prove untenable. 

 As one of the phases of insect biology to which this book is particularly 

 devoted is that which includes the study of habits, activities, or behanor, 

 we may dispense with any special discussion of instinct in this introductory 

 chapter. It is sufficient to say that no other class of invertebrate animals 

 presents such an interesting and instructive psychology as the insects. 



