BEGINNING OF NERVES. 



309 



Now, in this experiment, when the spiral strip is only made about half 

 an inch broad, it may be made more than a yard long before all the bell 

 is used up in making the strip ; and as nothing can well be imagined as 

 more destructive of the continuity of a nerve-plexus than this spiral 

 mode of section must be, we cannot but regard it as a very remarkable 

 fact that the nerve-plexus should still continue to discharge its functions. 

 Indeed, so remarkable does this fact appear, that to avoid accepting it 



Fig. 4. 



"we may well feel inclined to resort to another hypothesis — namely, that 

 these contractile waves do not depend for their passage on the nervous 

 network at all, but that they are of the nature of muscle-waves, or of 

 the waves which we see in indifferentiated protoplasm, where all parts 

 of the mass being equally excitable and equally contractile, however 

 severely we cut the mass, so long as we do not actuallj^ divide it, con- 

 tractile waves will pass throughout the whole mass. But this very rea- 

 sonable hypothesis of the contractile waves in the Medusce being possibly 

 nothing other than muscle-waves, is negatived by another fact of a most 

 extraordinary nature. At the beginning of this article I stated that the 

 distinguishing function of nerve consists in its power of conducting 

 stimuli to a distance, irrespective of the passage of a contractile wave ; 

 and I may here add that, when a stimulus so conducted reaches a gan- 

 glion or nerve-centre, it causes the ganglion to discharge by so-called 

 " reflex action." Now, this distinguishing function of nerve can plainly 

 be proved to be present in the Medusce. For instance, take such a sec- 

 tion of Aurelia as this one (Fig. 5), wherein the bell has been cut into 

 the form of a continuous parallelogram of tissue with the poiypite and 



