110 THE WHENCE AND THE WHITHER OF MAN 



food to the mouth, to keep the digestive sack in con- 

 tact with it, and for other purposes. A little higher 

 they are used to enable the animal to go in search 

 of its food. They are still, however, more or less 

 entirely subservient to digestion. But in the highest 

 worms we are beginning to see signs that muscles are 

 predominating in the body ; and we feel that, while 

 mutually helpful, the digestive system exists for the 

 muscles, and these latter are becoming the aim of de- 

 velopment. From worms upward there is a marked 

 advance in physical activity and strength. The muscles 

 thicken and are arranged in heavier bands. Skeleton 

 and locomotive appendages and jaws follow in insects 

 and vertebrates. The direct battle of animal against 

 animal, and of strength opposed to strength or activity, 

 becomes ever sharper. The strongest and most active 

 are selected and survive. 



And yet this is not the whole truth. Some power 

 of perception is possessed by every animal. But until 

 muscles had developed the nervous system could be of 

 but little practical value. Knowledge of even a great 

 emergency is of little use, if I can do nothing about it. 

 But when the muscles appeared, nerves and ganglion 

 cells were necessary to stimulate and control them. 

 And this highest system holds for a long time a posi- 

 tion subordinate to that of the lower muscular organ. 

 Its development seems at first sight extraordinarily 

 slow. Only in insects and vertebrates has it become a 

 centre of instinct and thought. Through the sense- 



* ' <_j 



organs it is gaining an ever clearer, deeper, and wider 

 knowledge of its environment. First it is affected 

 only by the lower stimuli of touch, taste, and smell. 

 Then with the development of ear and eye it takes 



