INNATE CAUSE OF MOVEMENT 37 



innate j character, self-caused and self-sustained. 

 Undisguised as is the control that the nervous 

 system exerts on our hearts, there is a cause of the 

 heart-beat that lies in the organ itself, and not in 

 any governance, however subtle and effective it 

 may be. The fundamental spontaneity of movement 

 is disguised, controlled, and rendered effectual in a 

 hundred ways, from the obvious exercise of our will 

 upon voluntary movement to the drilled soldier's 

 unthinking response to the word of command, the 

 unconscious acts of sleep and the automatic actions 

 of animals. But underlying that controlled muscular 

 force is the older, innate contractility perfected in 

 one special form — ciliary movement. 



Evolution of locomotor organs in animals. — In a 

 lowly organism, such as an earth- or water-worm, 

 the body consists of a muscular tube capable of 

 elongation and contraction, and of lateral undulating 

 wriggling movements. It is divided into rings, each 

 of which bears a number of hooks for the purpose 

 of creeping over the ground. In the more complex 

 annelids, as these creatures are called from their 

 segmented bodies, each ring grows out into two pairs 

 of leg-like processes, whereby the efficiency of pro- 

 gression over ground is increased. Special muscles 

 to move these limbs are formed, and the limbs them- 

 selves, in addition to bearing hooks, possess a leaf- 

 like outgrowth. Pairs of appendages occur on each 

 segment, and by their rhythmical action perform the 

 part of oars, sculling the body through the water, as 



