100 INSTINCT 



objects, although without a knowledge of the end they sub- 

 serve. There is so complete a gradation of responses 

 between simple reflexes and complex instincts that it be- 

 comes an arbitrary matter where the line is drawn between 

 them. In ourselves coughing, sneezing, winking, hiccough- 

 ing, swallowing, vomiting, jerking back when tickled or 

 painfully stimulated are commonly set down as reflexes. 

 Sucking, biting, chewing, spitting out, making a face over 

 disagreeable objects, grasping with fingers and toes, carrying 

 objects to the mouth, etc., are usually classed as human 

 instincts (Preyer). These acts are manifested by the human 

 infant at a very early period and in much the same way by 

 different individuals, and there can be no doubt that their 

 relation to the inherited organization is the same as in the 

 lower animals. Chewing, spitting out and making a face 

 over a disagreeable taste are little more complex than the 

 reflexes of swallowing and coughing. If not performed 

 involuntarily, there is at least a strong involuntary pro- 

 clivity to then* performance which would express itself in 

 action if not suppressed by an effort of the will. Swallowing, 

 coughing and sneezing are likewise capable of voluntary 

 suppression, so that we cannot separate these activities 

 sharply on the basis of their relation to the will any more 

 than on the ground of complexity. 



In man the gradation from the simple to the more com- 

 plex manifestations of instinct is not so obvious owing to the 

 fact that human instincts are so closely interwoven with 

 habits and the workings of intelligence; but in lower forms 

 where intelligence is reduced to a minimum the relation is 

 shown very clearly. In an animal such as the crayfish the 

 relation of instinct and reflex action may be studied very 

 advantageously by the experimental method. The cray- 

 fish has a number of well defined instinctive reactions such 



