CHAPTER XV 



IS THE BEHAVIOR OF THE LOWER ORGANISMS COMPOSED OF 



REFLEXES? 



The simplest reaction of an organism is the performance of a definite 

 simple act in response to a definite stimulus. Such is the contraction of 

 Vorticella, such the reversal of movement in a bacterium or in Para- 

 mecium or the flatworm. A simple responsive action of this sort is 

 commonly known as a reflex. The question has been raised as to 

 whether the behavior of the lower organisms differs from that of higher 

 animals in being purely reflex or not ; in other words, whether all their 

 reactions to stimuh are reflexes. For various organisms this question is 

 answered by many authors in the afiirmative. In some cases the be- 

 havior of animals much higher in the scale than most of those we have 

 considered is characterized as purely reflex. This is v. Uexkiill's view 

 for the sea urchin. We must examine briefly the question whether 

 behavior in these lowest organisms is properly characterized as reflex. 



What is a reflex? The concept of reflex action has had a complex 

 origin, and as a result it is defined in various ways. One of the phe- 

 nomena on which the concept is based is the contraction of a muscle 

 when a certain nerve is stimulated. The stimulation is supposed to pass 

 from the nerve to the spinal cord, whence it is reflected back to the mus- 

 cle; hence the name reflex. Some authors hold that the term can be 

 properly used only of acts thus performed by the aid of the nervous 

 system. This would of course exclude reflexes from the behavior of 

 unicellular organisms, and introduce uncertainty in dealing with the 

 lower Metazoa, for in many of these we do not know whether the re- 

 actions are throughout mediated by the nervous system or not. But it 

 is more usual to consider the reflex as a certain type of action, without 

 regard to the particular anatomical structures involved. Even where 

 the term is limited to actions produced through the nervous system, some 

 other term is employed to indicate the corresponding type of action in 

 animals without a nervous system, so that the existence of a particular 

 kind of action, indicated usually by the word " reflex," is recognized. 

 Thus, Beer, Bethe, and v. Uexkiill (1899) use for reflexes performed 

 without a nervous system the word "antitype." We may then ex- 



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