276 



A. J. Carlson. 



It was stated that the point of application of the proximal 

 electrodes to the cord was always three or more segments distant 

 from the reacting portion. This was done with two ends in 

 view, namely, to prevent escape of the current directly on to 

 the muscle and to prevent errors in the measurements from stimu- 

 lation of a more direct nervous mechanism on proximal than on 

 distal stimulation. In the annelids the cell bodies of the motor 

 neurones to the musculature of any one segment are situated in 

 the ganglia of the same segment as well as in the ganglia of the 

 adjoining anterior and posterior segments. The conditions are 

 in all probability the same in the nerve-cord of the centipedes and 



Fig. 6. — Juks. 



Tracings of the contraction of the posterior segments on distal and proxi- 

 mal stimulation of the cord. Length of cord, 5 cm. Transmission time of the 

 impulse, 0.24 sec. Rate, 21 cm. per sec. Time, 50 d. v. per sec. 



the millipedes. Now, if the cord is stimulated in the segment next 

 to the reacting portion it is probable that some of the neurones 

 to the reacting musculature are stimulated directly, while when 

 the cord is stimulated at a point 5 to 14 cm. further away these 

 neurones are probably stimulated indirectly; in other words, there 

 is probably "synapses" at the junction of the longitudinal con- 

 ducting paths in the cord and the motor cells to each segment. At 

 such junctions the propagation of the nervous impulse is in all 

 probability retarded. If therefore the latent time in the records 



