ILLUSTRATED AMONG PROTOZOA. 105 



requires the co-ordination of the movements of 

 several muscles. The nervous co-ordination neces- 

 sary to perfectly regulate such muscles so that 

 each shall act in its required time, and in proper 

 succession one after the other, can only have been 

 perfected by practice in the individual, and therefore 

 by practice in the race. One of the effects of 

 this practice has been an association of primarily 

 independent activities, — subconscious nervous asso- 

 ciation similar to mental association. This associa- 

 tion we must suppose to be a new arrangement of 

 the nervous elements, whereby actions formerly 

 independent should always occur most readily in 

 a certain definite relation to each other. In this 

 way only can we picture to ourselves the origin 

 of such complicated muscular movements as the 

 rhythmic beating of the heart, the origin of the 

 mechanism by which the equilibrium of a living 

 body is maintained, or the origin of any bodily 

 agility or manual dexterity. It must be regarded 

 as a universal property of living matter, that the 

 effects of its activity are perpetuated in itself as 

 the perfecting results of repetition, and as associa- 

 tion, — the activity itself being caused, as we have 

 seen, by energy absorbed from the environment. 

 The effects, also, of organic activity, of practice and 

 repetition, must, in some way, be transmitted from 

 generation to generation. 



