68 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



contraction waves which now originate from the 

 ganglion must either become blocked and cease to 

 pass round the disc, or they must zigzag round and 

 round the tops of these overlapping cuts. Now, 

 remembering that the passage of these contraction 

 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 overlapping 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 contraction wave. Yet this is not the 

 case ; for even in a specimen of Aurelia so severely 

 cut as the one here represented, the contraction 

 waves, starting from the ganglion, continued to 

 zigfzao- round and round the entire series of sections. 

 The second mode of section to which I have 

 alluded is as follows (Fig. 10). The central circle {x) 

 stands for an open space cut out of the umbrella ; 

 the outer circle indicates the margin of the animal, 

 with all lithocysts save one (I) removed ; and the 

 median circular line represents a cut. It will be 

 seen that the effect of this cut is almost completely 

 to sever the mass of tissue at z from the rest of the 

 umbrella, the only connection between them being 

 the narrow neck of tissue at z. Yet, in the case 

 to which I refer, the contraction waves emanating 

 from I passed in the directions represented by the 

 arrows without undergoing any appreciable loss of 

 vigour. Upon completing the circular cut at z, the 

 ring of tissue (y z) became totally paralyzed, while 



