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University of California Publications in Zoology [VOL. 18 



possible to use the full length of the worm. One characteristic of this 

 type of action is that it seems to be related solely to the longitudinal 

 muscles in contrast to that of the locomotor nerve fibers which set up 

 complex reactions in both circular and longitudinal muscles. 



Responses resulting from stimulation of these large fibers are always 

 exceedingly rapid as compared with other movements of the worms. 

 The reaction may be slight or violent, according to the amount of 

 stimulus applied, but any response travels the length of the worm in 

 a very short time. It is interesting to note the antagonistic relations 

 of the innervation of muscles when a quiescent worm is stimulated 

 lightly, with a sharp needle, at the anterior end ; immediately there is 

 a response by a relaxation of the circular muscles near the posterior 

 tip so that this part is flattened and enlarged. If the stimulus is made 

 stronger, this reaction will be followed by a jerk of the longitudinal 

 muscle and when the stimulus is moderately strong the contraction of 

 the longitudinal muscle is so quick and extensive that no reactions 

 of the circular muscle can be detected. 



A number of determinations for speed of this rapid action are 

 recorded in the accompanying table. The range of variation is large, 

 due in part at least to the methods of measurement and the inaccur- 

 acies of the apparatus (fig. 14). 



Fig. 14. Frequency polygon which shows the speed of impulse through giant 

 fibers. The figures represent millimeters per second. The mode is between 1000 

 and 1500 millimeters per second. 



All of these measurements were made on the large garden worm, 

 Helodrilus caliginosa, and as nearly as possible under the same con- 

 ditions. The interesting feature of this array of figures is that they 

 are high compared to those obtained in locomotor transmission. Ordin- 

 arily they can be said to be fifty times faster, and may even be one 

 hundred times faster, than the other type of transmission. The 

 mode for these few measurements is around 1500 millimeters per 

 second. While this is not so rapid as some recorded by Carlson and 

 Jenkins (1903) (table 1), in measurements on marine annelids, it is 

 certain that it belongs in the same class of phenomena as they were 



