122 University of California Puhlications in Zoology [Vol. 18 



the muscle has no property of rhythmic contractility. While this does 

 not show that transmission of impulse passes over many ganglia in 

 locomotion it strengthens the work of Biedermann (1904) and Bud- 

 ington (1902) who hold the theory of nervous control. 



Rates of Transmission of Locomotor Impulses 



Prohlem. — The fact that locomotor impulses could be transmitted 

 through a portion of the nerve cord isolated from segmental muscle 

 connections led to the query, what is the speed of these impulses? If 

 the speed were rapid it would mean that there were some fairly long 

 neurones in the cord, and if the speed were slow it could be interpreted 

 on the basis of short neurones and many synapses. This study should 

 throw some light on the structural basis of transmission. 



Discussion. — Jenkins and Carlson (1903) measured the rate of 

 nerve impulses in several species of annelids. The rates were found 

 to be exceedingly variable, from 89 centimeters in Nereis sp. to 694 

 centimeters per second in Bispiva polymorplia. The question these 

 investigators raised was whether they were dealing with simple con- 

 tinuous nerve fibers or with a very complex nervous tract. While the 

 anatomical connections of neurones in the cord have been worked out 

 to some fair degree of certainty, no long connections have been estab- 

 lished in the cord, except by the giant fibers. Jenkins and Carlson 

 left the question open as to whether their measurements were those of 

 a direct nervous path or an indirect one. 



After observing a very large number of experiments on the trans- 

 mission of the impulses as they pass through the etherized section of the 

 worm, and noting the slow progress of these as compared to the quick 

 end to end jerk of the worm when stimulated, there is little doubt 

 in my own mind but that the cord has two kinds of transmission of 

 nerve impulses. First, the very rapid impulses through giant fibers, 

 which result in vigorous contractions, as in the jerking back into their 

 burrows of the worms when strongly stimulated ; and the second type, 

 the impulses in the short fibers in the middle of the nerve cord, which 

 offer a complex path and so transmit impulses slowly down the cord. 



My records for the speed of impulses in the giant fibers agree quite 

 well with the speed recorded by Jenkins and Carlson (1903). The 

 method which these workers used was such that only the action of 

 quick contractions was recorded and no attempt was made to separate 

 this phenomenon from that of the locomotor impulses. As has been 

 shown, these latter impulses run but short distances in the cord unless 



