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youngster, the weaker, flat on his back, with arms and 

 legs upraised, fights playfully in self-defense, while the 

 other, on top, pummels and claws him in neck and ribs 

 in a playful effort to excite him, the mimic contest not 

 infrequently terminating in a real fight in which the 

 same parts are vigorously attacked. 



The fact that animals fight effectively in the dark and 

 always according to the habits of their species would 

 seem to suggest strongly that fighting is not an intelli- 

 gent occupation, but a reflex process, dependent solely 

 upon the infliction of blows in responsive areas ; and to 

 be explained, as Sherrington explains the reflex processes 

 of walking or running, as a succession of varying pres- 

 sures occurring in the feet, joints and limbs, by which 

 is produced a series of stimulations and responses which 

 appear in aggregate as the harmonious "habit" of 

 locomotion. 



The relation of tickling to laughter is an interesting 

 feature of this reflex and will be referred to later when 

 we discuss the phenomenon of laughter. Just now it 

 is sufficient to note that there is no laughter in response 

 to tickling by an insect, but boisterous laughter on 

 stimulation of the deep ticklish areas. The expendi- 

 ture of energy in each case is proportional to the phy- 

 logenetic demand of the original condition which gave 

 rise to the reflex. Indeed each type of the tickle reflex 

 is an excellent example of a specific response to specific 

 excitation. 



Phylogenetic Origin of Specific Reflexes 



As the tickle reflexes have been developed in response 

 to attacks by insects and carnivora, so other material 



