70 MAN AN ADAPTIVE MECHANISM 



with a consequent quick retraction of the hand and arm ; 

 while in the same child stimulation of the distance 

 ceptors of sight by the image of a pot of jam on the 

 pantry shelf will cause a continuous discharge of energy 

 for a long series of motor acts. 



Had distance ceptors never been developed, life would 

 have remained on the plane of stationary animals, 

 such as the sponge. The inner processes, those con- 

 nected with circulation, respiration, digestion and 

 elimination, might have been developed through contact 

 stimulation, but incentive to penetrate into the dis- 

 tant environment would never have been realized. 

 In other words, the evolution of distance ceptors in 

 animals is correlated with the evolution of their powers 

 of free movement. 



In his work on the " Integrative Action of the Nervous 

 System," Sherrington clearly emphasizes the impor- 

 tant connection between distance ceptors, locomotion 

 and the upbuilding of the higher brain functions, and 

 gives some interesting confirmatory examples of the 

 simultaneous disappearance of sense organs and loss of 

 locomotion in animals which metamorphose from an 

 active motor life to one of a sedentary character. 

 Certain species of the Ascidia and barnacles, for in- 

 stance, are animals which are suddenly transformed 

 from a larval life of active locomotion to one of inactiv- 

 ity when in the course of their development they become 

 attached to some fixed object in their environment. 

 The Brachiopod, for example, at first possesses a loco- 

 motor mechanism and a well-developed visual organ. 

 When it suddenly relinquishes larval life and becomes 

 permanently attached to a fixed object, the highly de- 



