110 DEVELOPMENT AND HEREDITY. 



ism, and stimulate as smell ; next, the particle itself 

 strikes against the organism, and there is a stimulus 

 of contact; then the process of absorbing — caused 

 by contact, capillarity, etc. — brings the protoplasm 

 to flow toward and around the particle. Thus the 

 sequence of reaction is first smell, then contact, and 

 then movement in the direction whence the smell 

 and contact have come. If this simple sequence 

 were repeated often enough, an association of the 

 reactions would arise. This association might event- 

 ually become so strong — through repetition — that 

 the movement in the direction toward the gaseous 

 effluvia might follow after the smelling, even when 

 the stimulus of contact did not occur. We can 

 thus imagine how the co-ordinations arose which 

 control the search for food and locomotion. 



Let us suppose, further, that owing to scarcity of 

 food or to increase of size, the organism is stimu- 

 lated to movement by hunger, or perhaps by asphyxi- 

 ation caused by remaining in water fouled by its own 

 carbon dioxide. The loss of food and oxygen would 

 cause a stoppage in the natural chemical change 

 going on in the mass ; thus there would be a dis- 

 turbance in the inner equilibrium of forces, which 

 might readily cause slight movement in different 

 parts of the soft mass. The hunger and dearth of 

 oxygen would probably be conditions frequently 



