CHAPTER XII 



GENERAL FEATURES OF BEHAVIOR IN OTHER LOWER 



METAZOA 



THE foregoing chapters attempt to give a connected systematic 

 account of behavior in the Protozoa and the Ccelenterata. These 

 may serve as types of the lower organisms. The necessary spatial 

 limits of the present work render impossible a similar treatment of 

 other groups. We must content ourselves therefore with a survey of 

 some of the main features of behavior in some other invertebrates. 

 We shall take into consideration chiefly the lower groups. 



i. DEFINITE REACTION FORMS ("REFLEXES") 



In the action systems of most organisms we find certain well-defined 

 reaction forms, or what are often known as reflexes, 1 which make up a 

 large proportion of the behavior. In the groups we have thus far con- 

 sidered, such definite reaction types are seen in the avoiding reactions 

 of infusoria, the definite contractions occurring in response to stimuli 

 in the Protozoa and Ccelenterata, the bending of the tentacles toward 

 the mouth when stimulated by food, in the hydroids and sea anemones, 

 and in many other features of the behavior. It is true, as we have 

 seen, that even these so-called reflexes are usually variable when studied 

 in detail, and their occurrence and combination depend upon a mul- 

 tiplicity of internal as well as external conditions. Yet certain elements 

 of behavior do occur in accordance with a definite type, and this fact 

 is one of much importance. In some lower animals behavior is largely 

 made up of such definite reaction forms. This fact has assumed an 

 overshadowing importance in much recent work on behavior; investi- 

 gation has taken largely the form of a search for precisely definable 

 reflexes and tropisms, and for conditions under which they occur in the 

 typical way, while other factors in the behavior have been neglected. 

 Since these matters have been so much dwelt upon, we need not take 

 them up in great detail in the present work. 



The best-known case of behavior made up largely of such definite 



1 The use of this term will be discussed later. 

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