Physiology of Vetitral Nerve Cord of Myriapoda. 281 



The rapidity of propagation of the antero-posterior nervous 

 impulse in the cord is the same in the two centipedes Scolopendra 

 and Scolopocryptops. These two centipedes are also closely alike 

 in the number of segments and in the swiftness of their reactions 

 and movements. The rate is lower than one might have expected, 

 judging by the quick movements of these animals. While it is 

 higher than the rate in the ventral nerve-cord of some of the 

 worms, it is only about one-half that in the nerve-cord of the higher 

 marine annelids Glycera, Eunice and Bispira (one of the Sahel- 

 lidae) . 



The great difference between the rate in Scolopendra and Scolo- 

 pocryptops on the one hand and that in Himantarium on the other 

 is probably due to a greater number of "synapses," that is, a great- 

 er complexity of the conducting path in the cord of the latter. Him- 

 antarium exhibits a much greater segmental independence than do 

 the other two centipedes. In Himantarium the progression of the 

 contraction from the point of stimulation is slow enough to be ob- 

 served by the eye, while in Scolopendra every segment of the body 

 seems to contract at the same time on stimulation of the nerve-cord 

 at any one point. In view of the relatively low rate even in 

 Scolopendra it seems to me probable that the conducting path in 

 the cord is not made up of a system of uninterrupted nerve-fibers, 

 although it is evidently less complex than the corresponding con- 

 ducting path in Himantarium. 



The rate in the nerve-cord of the millipede is the lowest of all, 

 or only 20 cm. per sec. This is only one-third that of the lowest 

 rate recorded in the nerve-cord of the annelids, namely in the 

 leech (56 cm. pr sec), and in the marine worm Aphrodite (55 

 cm. per sec). The reactions and movements of Jules are also 

 much slower than those of Scolopendra or Scolopocryptops. 

 From the fact that the rate of conduction of the impulse in the 

 nerve appears to stand in direct relation to the rapidity of the 

 processes of contraction in the muscle supplied by the nerve, ^ it 

 seems probable that the difference in the rate in Scolopendra and 

 Jules is not solely apparent and due to the greater complexity of 

 the conducting path in the latter animal. 



^Carlson, American Journal of Physiology, 1904. IX, p. 401. 



