282 A. J. Carlson. 



A comparation of Tables II and III leaves no doubt that in 

 Scolopendra the rapidity of conduction of the impulse through 

 the cord is greater in the antero-posterior than in the postero-an- 

 terior direction. A similar condition exists in the case of the 

 spinal cord of the California Hagfish {Bdellostoma) and there 

 are indications of the same condition in the spinal cord of the 

 snake/ In the annelid Glycera, on the other hand, the rate in the 

 ventral nerve-cord is the same in both directions. ■ It is difficult 

 to understand how this difference in the rate of conduction of the 

 postero-anterior and the antero-posterior nervous impulses has 

 come about in the course of development. For the preservation 

 of the individual it would seem that a rapid transmission of the 

 nervous impulse is just as essential over the sensory part of the 

 reflex arch as over the motor part. 



II. The Reflex Functions of the Ventral Nerve-Cord and the 

 Segmental Ganglia. 



The great difference in the rate of propagation of the nervous 

 impulse in the cord of Scolopendra and Himantariiim lead to the 

 study of the reactions and locomotions of these animals under 

 natural conditions as well as of the reflexes exhibited after sever- 

 ance of the head segment, together with the supra-oesophageal 

 ganglion or "brain," in order to determine whether these ani- 

 mals exhibit other differences in conformity with the difference 

 in the rate of the nervous impulse. 



Himantarium has two modes of locomotion, namely, by means 

 of its legs and by means of series of contraction waves passing 

 from one end of the. body to the other exactly as in the worms. 

 These movements are so identical with those of the worms that 

 the muscular mechanisms are probably the same or at least simi- 

 lar. The centipede works its legs at the same time that it resorts 

 to the other method of getting over the ground. The worm 

 method of locomotion comes into play only when the anmal is in 

 a hurry to get away from an enemy. It is made use of with 



^Carlson, Archiv fiir die gesammte Physiologic, 1904, Ci, p. 231. 

 -Jenkins and Carlson, loc. cit. 



