THE SPECIAL SENSE ORGANS 233 



The three senses that enable the organism to obtain stimuli 

 from objects at some distance from the body— sight, hearing, 

 and smell — give opportunity to discover food or enemies while 

 there is still a little time before action is imperative. We find, 

 accordingly, that although there are many reflexes set up by 

 these senses, there are also many situations in which the stim- 

 ulus does not bring out an immediate reaction. The impres- 

 sions obtained through these senses somehow register in the 

 brain cells and set up activities later. It is in some such way 

 that we are capable of learning from experience ; the delayed 

 reaction gives an opportunity to react in one of several differ- 

 ent ways, and the way selected depends upon previous experi- 

 ence. It is probably in the delayed reaction that the organism 

 makes a beginning at control— coniroX of itself and so control 

 of its environment. 



THE SPECIAL SENSE ORGANS 



1. Relation of nervous system to adjustment 



Through reflexes Through delayed reactions 



Through acquired (learned) reactions 



2. Relation of nervous system to unification of organism 



In coordination of movements 



In coordination of systems of organs 



3. Specialized sense organs 



Mechanical Chemical 



Touch Taste 



Gravity Smell 



Light Sound 



Seeing Hearing 



4. Relation of sense organs to control of environment 



Near perception Distant perception 



Limit to perfection of reflexes 



QUESTIONS 



1. How do reflexes enable living things to get what they need ? 



2. How do reflexes enable living things to escape dangers ? 



3. What would happen if every animal had perfect reflexes for getting 

 food (catching prey) and perfect reflexes for escaping enemies ? 



