128 University of California Publications in Zoology [Vol. 18 



The physiology of these reactions is correlated with the anatomy 

 of these fibers. The path is a direct one and the speed of their 

 impulses is fast, 1500 millimeters per second compared with 25 milli- 

 meters per second for locomotor reflexes. The connections are simple 

 and the reactions are concerned largely with the contractions of but 

 one set of muscles, the longitudinal muscles. The fibers run the full 

 length of the cord and so reactions are concerned with the whole 

 animal. They are single fibers and produce a single action. There 

 is no wave motion nor evidences of loss as the stimulus passes down 

 the cord. 



There is no reason to suppose that these fibers have anything to do 

 with locomotor reflexes or transmission ; everything points to a separate 

 function for these large long fibers. 



Conclusion. — We have taken for granted that Friedlander 's (1891) 

 suggestion that the end to end movements are due to impulses carried 

 by the giant fibers. The results of this work on rates of transmission 

 seem to justify this supposition. No theory allows a nerve to have for 

 itself more than one rate of transmission. The speed of one type of 

 action and the slowness of the other would necessitate two kinds of 

 fibers. The anatomical conditions and the physiological reaction are 

 easily correlated. The large giant fibers are continuous structures 

 running the full length of the worm and capable of carrying the 

 impulses swiftly from end to end at a normal rate of 1500 millimeters 

 per second, while in the center of the nerve cord are numerous short 

 neurones running short distances up and down the cord, giving a 

 complex path, with slow speed of transmission, normally 25 milli- 

 meters per second, such as would be expected on account of the 

 multiplicity of synapses. 



THEORETICAL CONSIDERATIONS 



The Nervous Mechanism. Some of the most salient facts brought 

 out in the study of transmission are : the nervous system plays an 

 essential part in the movements of locomotion; the impulses respon- 

 sible for the waves of contraction are capable of running for con- 

 siderable distances in the cord and are not confined to one or two 

 segments, as indicated by Friedlander; transmission may extend over 

 as many as twenty segments without intervening muscular activity, 

 the rate of transmission is a variable one becoming slower as it pro- 



