274 ^- J- Carlson. 



current was therefore used as stimuli. A single induced shock 

 applied at one end of the nerve-cord of the millipede Jules pro- 

 duces progressive movements of the ambulatory appendages or 

 legs from the point of stimulation to the opposite end of the ani- 

 mal, but the contraction of the muscles moving the body seg- 

 ments is confined to the immediate vicinity of the point of stimu- 

 lation; but a short series of the tetanizing current produces con- 

 traction of these muscles in all the segments of the body. A 

 similar condition was found by Dr. Jenkins and myself to obtain 

 in the marine annelid Aphrodite, in which a single induced shock 

 applied to the ventral nerve-cord produced contraction of the 

 muscles that move the setae, but a tetanizing current was required 

 to produce contraction of the muscles moving the segments. It 

 is therefore probable that the nervous mechanism of the setae in 

 Aphrodite and of the legs in the millipede Is less complex and 

 more readily excited than is the nervous mechanism in connection 

 •with the muscles that move the segments. If one of the setae in 

 the worm and one of the legs of the millipede could be used for 

 raising the lever and the rapidity of transmission of the impulse 

 In this nervous mechanism thus measured, it would undoubtedly 

 be found to be several times greater than that in the nervous 

 mechanism to the segmental muscles. 



The character of the records produced by the contraction of 

 the reacting portion on stimulation of the nerve-cord may be 

 gathered from the typical tracings reproduced in Figs. 2 to 6. 

 Only the first part of the tracings showing the latent period and 

 the amplitude of contraction is given, as these are the only points 

 with which we are concerned. In the records from the millipede 

 (Fig. 6) the rising curves represent the gradual bending ventral- 

 wards of the reacting portion, the movements of each segment 

 fusing into one, apparently continuous, contraction. Each stimu- 

 lation of the cord by a tetanizing current of short duration 

 usually produces but one such movement. The records from the 

 centipedes are more irregular from the fact that each stimulation 

 of the cord usually starts a series of movements or rather con- 

 tractions and relaxations which may last for a minute or two in 

 the fresh preparations. 



