66  JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
to be overspread with a dise of muslin, the fibres 
and mesh of which are finer than those of the finest 
and closest cobweb, and if he will imagine the mesh 
of these fibres to start from these marginal ganglia, 
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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 continues to supply its 
rhythmical discharges to the muscular sheet of the 
