312 THE POPULAR SCIENCE MONTHLY. 



perhaps erroneous, and that, in any case, when stained with gold, some 

 of the nervous channels show themselves in the form of fully differ- 

 entiated nerves. Now this fact, it is needless to say, greatly enhances 

 the interest of the previous experiments. If, as I formerly said, the 

 proof of vicarious action being possible to an almost unlimited extent 

 in these incipient nerve-fibres appeared to me one of the most interesting 

 among the additions to our knowledge of invertebrate physiology, much 

 more interesting does this proof become if we further learn that these 

 incipient nerve-fibres are only incipient in the sense of constituting the 

 earliest appearance of nerve-fibres in the animal kingdom. For if these 

 true nerve-fibres admit, from the peculiarly favorable plan of their ana- 

 tomical distribution, of being proved to be not improbably capable of 

 vicarious action to so extraordinary a degree, we may become the more 

 prepared to believe that nerve-fibres elsewhere are similarly capable of 

 vicarious action. But the interest does not end here, for Mr. Schafer's 

 numerous preparations all show the highly remarkable fact that the 

 nerve-fibres which so thickly overspread the muscular sheet of Attrelia 

 do not constitute a true plexus, but that each fibre is comparatively 

 short, and nowhere joins with any of the other fibres. That is to say, 

 although the constituent fibres of the network cross and recross one 

 another in all directions — sometimes, indeed, twisting around one an- 

 other like the strands of a rope — they can never be actually seen to 

 join, but remain anatomically isolated throughout their length. So 

 that the simile by which I have represented this nervous network — the 

 simile, namely, of a sheet of muslin overspreading the whole of the 

 muscular sheet — is as a simile even more accurate than has hitherto ap- 

 peared ; for just as in a piece of muslin the constituent threads, although 

 frequently meeting one another, never actually coalesce, so, in the 

 nervous network of Aurelia, the constituent fibres, although frequently 

 in contact, never actually unite. 



Now, if it is a remarkable fact that in a fully differentiated nervous 

 network the constituent fibres are not improbably capable of vicarious 

 action to almost any extent, much more remarkable does this fact 

 become when we find that no two of these constituent nerve-fibres are 

 histologically continuous with one another. Indeed, it seems to me 

 that we have here a fact as startling as it is novel. There can scarcely 

 be any doubt that some influence is communicated from a stimulated 

 fibre a to the adjacent fibre h at the point where these fibres come into 

 close apposition. But what the nature of the process may be whereby 

 a disturbance in the excitable protoplasm of a sets up a sympathetic dis- 

 turbance in the anatomically separate protoplasm of b, supposing it to 

 be really such — this is a question concerning which it would as yet be 

 premature to speculate.' But if, for the sake of a name, Ave call this 



* That it can scarcely be an electricalli/ inductive effect would seem to be shown by 

 the fact that such effects can only be produced on nerves by strong currents ; and also 

 by the fact that the salhie tissues of the swimming-bell must short-circuit any feeble 

 electrical currents as soon as they are generated. 



