Physiology of Ventral Nerve Cord of Myriapoda. 275 



Because of the very complex nature of the muscular part of 

 the preparation the character of the curves, that is, the rapidity 

 and the amplitude of the contraction is not a very accurate guide 

 in determining the admissability of individual records. For ex- 

 ample, two successive tracings produced by stimulation of the 

 cord at the distal or at the proximal point may show great diverg- 

 ence in the amplitude of the contraction and yet exhibit the same 

 latent period or they may be nearly identical in the amplitude 

 and rapidity of the contraction and yet show a difference in the 

 latent period of from 15 to 25%. The tracings that showed a 

 greater difference in the amplitude of the contractions than is 

 exhibited by the records in Fig. 3 were usually excluded. 



Fig. 5. — Himantarium. 



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

 mal stimulation of the cord. Length of cord, 14 cm. (120 segments). Trans- 

 mission time of the impulse, 0.52 sec. Rate, 27 cm. per sec. Time, 50 d. v. 

 per sec. 



Of the centipedes worked on the best preparation for these ex- 

 periments is obtained from Scolopendra. The largest specimens 

 yield a length of nerve-cord between the distal and the proximal 

 points of stimulation of from 5 to 6 cm. This centipede is rela- 

 tively stout and the reacting segments amply able to lift the re- 

 cording-lever. Himantarhim is more than twice as long as Scolo- 

 pendra, but is so slender that it is even difficult to fix the specimen 

 to the platform without injuring the nerve-cord with the pins. 

 For the experiments on this centipede the recording-lever had to 

 be very light. 



