Facts and Factor's of Development 



39 



becomes differential sensitivity and special senses in the proa 

 of embryonic differentiation. Such sensitivity is the basis of all 



psychic processes; sensations are the elements of the mind. 



2. Reflexes, Tropisms, Instincts. — All the responses of germ 



a 



Fig. i6, a, b, c. Repulsion of Spirilla by Common Salt, a, condition 

 immediately after adding crystals; b and c, later stages in the reaction. 



.r, y. Z, repulsion of Spirilla by distilled water. The upper drop consists 

 of sea-water containing Spirilla, the lower drop, of distilled water. At x 

 these have just been united by a narrow neck; at y and z, the bacteria 1 

 retreated before the distilled water. (From Jennings, after Massart.) 



