1918] Bovard: Nervous Impulses in the Earthworm 127 



TABLE 1 



SUMMARY OF RATES IN WORMS CARLSON AND JENKINS 



Species Direction Centimeters per sec. 



measuring. None of my measurements approached the highest speeds 

 in these marine forms, such as that in Bispira polymorpha, viz., 6940 

 millimeters per second, or even in Lumbriconereis sp., viz., 9370 milli- 

 meters per second, nor on the other hand did I find any as slow as 

 that in Cerebratulus at 54 to 90 millimeters. Several worms, Nereis, 

 Arenicola, Sthenelais, give averages about the same as that which I 

 found for Helodrilus. 



Jenkins and Carlson used averages in obtaining the figures above, 

 when it would seem such a variation in measurements occurred that 

 the mode is more nearly the correct expression. I have used this in 

 both series, that on locomotor transmission and on giant fiber action. 



One feature of giant fiber action that is easily noticed is, that, 

 once started, it always goes through to the posterior end ; it never dies 

 out in transit as the locomotor waves do. In cases where the nerve 

 cord has been severed, the impulse runs as far as the cut, and never 

 beyond. 



Krawany (1905) in his discussion of the elements in the central 

 nerve cord describes the relations of the giant fibers to the association 

 cells in the cord. These large fibers pass from end to end of the nerve 

 cord and in each ganglion send out branches which are intimately in 

 connection with processes from association cells in the middle group. 

 These cells which thus synapse with the direct fibers never have cross- 

 over connections but seem to be entirely homolateral. 



