132 University of California Publications in Zoology [Vol. 18 



association tracts, and that if these stimuli are heavy they add to the 

 strength of stimulus passing along, or if weak add little or nothing at 

 all, then we have a basis for explaining the variations in rate. In 

 each ganglion there will be at least one and maybe two synapses to be 

 passed, each with a certain resistance which will tend to cut down the 

 force of the stimulus and its power to get through. Each synapse in 

 each segment resists the passage of the locomotor impulse but in 

 ordinary locomotion each well coordinated contraction wave reinforces 

 the loss and the movement runs the full length of the worm. The 

 uncertain limit of such transmission then can be understood for many 

 factors may come in to change the force of the stimulus ; the stimulus 

 may have started in a weak contraction — outside conditions may have 

 altered the amount of reinforcement — internal conditions in the cord 

 itself may have demanded a more complex path in one case than in 

 another, or even the physiological condition of the worm may have had 

 some effect on the resistance in the synapses. 



SUMMARY 



1. "When a worm is anesthetized in the middle area and the peri- 

 pheral nerves are rendered useless, locomotor impulses may be trans- 

 mitted in both directions through the nerve cord of this middle region 

 from anterior to posterior, and posterior to anterior. 



2. Tension or pull, while important in normal creeping movements, 

 may be eliminated and the locomotor stimuli will still pass up and 

 down the cord for some distance. 



3. Nerve free preparations show that locomotor impulses may 

 travel considerable distances in the cord. Under such conditions the 

 anterior and posterior. parts act in perfect coordination. When the 

 nerve is cut such coordination ceases. Stovaine when applied to the 

 nerve cord blocks the passage of locomotor impulses up and down and 

 the coordination of anterior and posterior parts is lost; as soon, how- 

 ever, as the effects of the drug are removed impulses again pass freely 

 in the cord and coordination returns. 



4. The results of measuring the limits of transmission of the loco- 

 motor impulses shows that no absolute limits can be set. The impulses 

 travel short distances of ten segments very readily but when required 

 to traverse a longer section of twenty-eight segments the difficulty is 

 great. No records show impulses passing through as many as thirty 

 segments. 



