3o8 



THE POPULAR SCIENCE MONTHLY. 



the ganglia are collected into these eight marginal bodies, as proved 

 by the fact that on cutting out all the eight marginal bodies paralysis 

 of the bell ensues. Therefore, if the reader will imagine this diagram 

 to be overspread with a disk of muslin, the fibres of which start from one 

 or other of these marginal ganglia, he will gain a tolerably correct idea 

 of the lowest nervous system in the animal kingdom. Now suppose that 

 seven of these eight ganglia are cut out, the remaining one then con- 

 tinues to supply its rhythmical discharges to the muscular sheet of the 

 bell, the result being, at each discharge, two contractile waves, which 

 start at the same instant, one on each side of the ganglion, and which 

 then course with equal rapidity in opposite directions, and so meet at 



the point of the disk which is 

 opposite to the ganglion. Sup- 

 pose now a number of radial cuts 

 are made in the disk, according 

 to such a plan as this, wherein 

 every radial cut deeply overlaps 

 those on either side of it. The 

 contractile waves which now ori- 

 ginate from the ganglion must 

 either become blocked and cease 

 to pass round the disk, or they 

 must zigzag round and round the 

 tops of these overlapping cuts. 

 Now, remembering that the pas- 

 sage of these contractile waves 

 is presumably dependent on the 

 nervous network progressively distributing the ganglionic impulse to 

 the muscular fibres, surely we should expect that two or three overlap- 

 ping cuts, by completely severing all the nerve-fibres lying between 

 them, ought to destroy the functional continuity of these fibres, and so 

 to block the passage of the contractile wave. Yet this is not the case ; 

 for, even in a specimen of Aurelia so severely cut as the one here rep- 

 resented, the contractile waves, starting from the ganglion, continued 

 to zigzag round and round the entire series of sections. 



The same result attends other forms of section. Here, for instance, 

 seven of the marginal ganglia having been removed as before, the 

 eighth one was made the point of origin of a circumferential section, 

 which was then carried round and round the bell in the form of a con- 

 tinuous spiral — the result, of course, being this long ribbon-shaped 

 strip of tissue with the ganglion at one end, and the remainder of the 

 swimming-bell at the other. Well, as before, the contractile waves 

 always originated at the ganglion ; but now they had to course all 

 the way along the strip until they arrived at its other extremity ; and, 

 as each wave arrived at that extremity, it delivered its influence into 

 the remainder of the swimming-bell, which thereupon contracted. 



