EXPERIMENTS ON WORMS 



the longitudinal muscles contract and the worm 

 becomes shorter. As the bristles are still turned 

 backward, the shortening can only be accomplished 

 by the approach of the posterior end toward the 

 head. The entire worm is therefore compelled to 

 move forward. What happens if Q 



we divide the ganglion-chain of 

 the animal in the middle of the 

 body, or if we remove some 

 ganglia from that region ? Will 

 the forward piece move inde- 

 pendently of the posterior piece ? 

 Benedict Friedlander has made 

 this experiment and found that 

 the coordination continues in spite 

 of the division of the central 

 nervous system (4). If the for- 

 ward piece begins to move, the 

 aboral piece will also move in the 

 same direction and at the same 

 rate. This overthrows the idea 

 that coordination in these animals 

 is determined by a special centre * su P races p ha g ea i 



* brain ; u, suboesophageal 



of coordination which is located in ganglion; A intestine; c, 



... T- i 1 i ganglia of the ventral cord. 



the brain. But how, then, does 

 the coordination take place ? When the forward 

 piece elongates and attempts to shorten itself by 

 contracting the longitudinal muscles, the skin of the 

 aboral piece is stretched. This pulling probably 

 acts as a stimulus which causes the longitudinal 



FIG. 28. SIDE VIEW OF THE 

 CENTRAL NERVOUS SYS- 

 TEM OF THE EARTH- 

 WORM. 



