1918] Bovard: Nervous Impulses in the Earthworm 133 



5. Spontaneous rhythmical movements are dependent on the 

 nervous system and the muscle tissues do not possess the property of 

 rhythmic contractility. This strengthens the theory that locomotion 

 is under nervous control. 



6. The speed of locomotor impulses is quite variable. The mode 

 that expresses the normal rate is about 25 millimeters per second. The 

 rate may be increased or decreased in transit from segment to segment. 



7. The rate of the transmission of giant fiber action is very rapid 

 when compared to that of the locomotor impulses. The mode for a 

 number of measurements shows the speed to be about the rate of 1500 

 millimeters per second. The wide gap between these two types of 

 nervous activity, the slow locomotor on the one hand and the rapid 

 giant fiber action on the other, indicates that these impulses are 

 mediated by two quite different kinds of nerve elements. 



8. The anatomy of the nerve cord as shown by Krawany and 

 Deschant has in it no long neurones. The processes may join suc- 

 cessive ganglia but none extend through the cord for a great distance 

 except the larger giant fibers, which run the full length of the cord. 



9. The peculiarities of the locomotor impulses in transmission, such 

 as the variability in rate of speed, and the slowness of it, can be 

 accounted for on the basis of the structure. The impulse to make its 

 way down the cord must pass in each ganglion at least one synapse, 

 and the possibility is that there would be more than this. Each synapse 

 would not only cut down the strength of the impulse but would also 

 slow down the speed because of the time consumed to cross the gap 

 between neurones. In normal creeping the impulses travel regu- 

 larly down the cord because each contraction of circular and longi- 

 tudinal muscle in each segment sends in locomotor impulses which 

 reinforce the impulse passing down the central nerve cord, and any 

 loss through the synapse is made up in this way. If for any reason 

 the muscular activity fail or if the nervous connections to the cord be 

 destroyed the locomotor impulse traveling down the cord in this region 

 would decrease in strength and decrease in rate because of the lack of 

 reinforcement. 



