142 COMPARATIVE PHYSIOLOGY 



In addition to observations on those animals in which it is 

 possible to isolate suitable lengths of nerve-axons, the observa- 

 tions of Jenkins and Carlson (1903) on conduction through 

 the nerve- cord of various worms are interesting, though the 

 values given are not necessarily comparable with the above, 

 since they involve conduction across synapses in the C.N.S. 

 All these data are derived from direct (graphical) observation. 



From these data it would appear that the rate of conduction 

 in annelids may be higher than in the lower vertebrates as 

 exemplified by the hagfish, Bdellostoma. Parker found that 

 the rate of transmission in the nerve-net of the sea-anemone 

 was about 13 cm. per second. 



Propagation takes place on either side of the point of 

 stimulation in opposite directions. This is shown by the 

 effects of stimulating the cut ends of fibres which bifurcate, 

 and by study of the electrical response which is an invariable 

 accompaniment of the nervous impulse. In seeking for 

 further light on the nature of the propagated disturbance, 

 certain facts clearly emerge from experimental investigation 

 upon the nerve-muscle preparation. These are : first, that 

 the disturbance depends upon a supply of energy distributed 

 along the whole course of the neurone, so that if an impulse 

 is once set up, its intensity is independent of that of the 

 stimulus which initiates it so long as other factors remain 

 constant ; second, that the transmission of the excited state 

 is associated with an electrical variation which travels along 



