HOiV ANIMALS KNOIV THINGS 



103 



As we proceed higher in the animal scale we find a 

 gradual grouping in definite positions of a number of 

 cells that are specially sensitive to the different influences 

 acting on the organisms, and along with this definite groups 

 of muscular cells and definite nerve pathways for impulses 

 to pass from the sensitive to the motor cells, and more 

 and more complex connections of groups with groups. 

 In the highest organisms we have sense-organs which 



Sunfisli. 



Sparrow. 



Mouse. 



Sp. Cd 



Fig. 69. —Diagram of brains of vetebratc-s; 01 f. Z., olfactory lobes; Clir., 

 cerebrum; Aid. Br., midbrain (opticlobes); Cbl., cerebellum; Aled. Ob., 

 medulla oblongata; Sp. Cd., spinal cord. (From specimens.) 



make us exactly acquainted with the outside world ; we 

 have brain, spinal cord, and nerves, which receive the 

 impulses from these and turn them through the muscles 

 into all the motions our bodies are capable of; besides 

 we have all those wonderful processes included under 

 what we call instinct, memory, and reason. 



The special senses and their organs — The organs 

 of sight, the eyes, are the only organs of special sense 

 generally conspicuous and unmistakably recognizable 

 when present. In the vertebrates the eyes, ears, nose, 

 and taste organs are always situated on the head, but 

 in the invertebrates the sense-organs corresponding to 

 these are often scattered over the body, and certain other 



