lyo 



NA TURE 



\_Aitgust 2, 1877 



is about the size of a soup-plate, and in it all the ganglia 

 of the margin are collected into the eight marginal bodies ; 

 so that on cutting out these eight marginal bodies total 

 paralysis of the bell ensues. But although the bell is 

 thus paralysed as to its spoitaneoiis movements, it con- 

 tinues responsive to stimulation ; for every time you 

 prick or electrify any part of the contractile sheet, a wave 

 of contraction starts from the point which you stimulate, 

 and spieids from that point in all directions as from a 

 centre. Such contractile waves, at ordinary temperatures, 

 irav el at about the rate of a foot and a half per second ; 

 and the important question with regard to them which we 

 shall have to consider to-night is this — Are they merely 

 of the nature of muscle-waves, such as we see in undit- 

 fcrentiated protoplasm, or do they require the presence of 

 rudimentary neive-fibres to convey them — the stimulus 

 w.ive in the ludimentary //tv-'f-fibres progressively causing, 

 as it advances, the co)iiractile wave in the rudimentary 

 mnscte-^hxti ? 



Now the great argument in favour of these contractile 

 waves being muscle-waves, and nothing more, is simply 

 this — that the contractile tissue is able to endure im- 

 mensely severe forms of section without the contr.ictile 

 waves in it becoming blocked. For instance, when the 

 lell of Aiire/ia is cut as here represented. Fig. 3, and any 

 pait of the circle is stimulated, a contractile wave radiates 



from the point of stimulation just as it did before the 

 cuts were introduced, notwithstanding the wave has now 

 to zig-zag round and round the ends of the overlapping 

 cuts. Similarly, if instead of employing artificial stimu- 

 lation, a single ganglion (g) be left in iitic while all the 

 other seven are removed, contractile waves will radiate 

 in rhythmical succession from the single remaining 

 ganglion, and course all the way round the disc. 

 Now this experiment seems to prove that the contractile 

 waves depend for their passage, not on the conductile 

 function of any primitive nervous net-work, but on the 

 protoplasmic qualities of the primitive muscular tissue. 

 The experiment seems to prove this, because so severe a 

 form of section would seem of necessity to destroy the 

 functional continuity of anything resembling such a 

 nervous net-work as we observe in higher animals. 



Here,again,Fig.4,isanotherform of section. Seven mar- 

 ginal bodies having been removed as before, the eighth one 

 was made the point of origin of a circumferentiafsection 

 which was then carried round and round the disc in the 

 form of a continuous spiral— the result, of course, being 

 this long riband-shaped strip of tissue with the ganglion 

 {g) 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 extrfm'ty, and as each wave arrived at that extre- 

 mity it delivered its influence into the remainder of the 

 swimming-bell, which thereupon contracted. Hence, 

 from this mndeof section as from the last one, the deduc- 

 tion rerlainly appears to be that the passage of the 

 contractile waves cannot be dependent on the presence of 

 a nervous plexus ; for nothing could well be imagmed as 





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more destructive of the continuity of such a pl.xus than 

 this spiral mode of section must be. 



Nevertheless there is an important body of evidence to 

 be adduced on the other side ; but as I can only wait to 

 state a few of the chief points, I shall confine my obser- 

 vations to the spiral mode of section. First of all, then, 

 I have invariably found it to be the case that if this mode 

 of section be carried on sufficiently far, a point is sooner 

 or later sure to come at which the contractile waves cease 

 to pass forward : they become blocked at that point. 

 Moreover, the point at which such blocking of the waves 

 takes place is extremely variable in different individuals 

 of the same species. .Sometimes the waves will become 



^,,1 



blocked when the strip is only an inch or less in length, 

 while at other times they continue to pass freely from end 

 to end of a strip that is only an inch broad and nearly a 

 yard long ; and between these two extremes there are all 

 degrees of variation. Now if we suppose that the in- 

 fluence of the ganglion at the end of the strip is propa- 

 gated as a mere muscle-wave along the strip, I cannot see 



