72 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
we cut the mass, as long as we do not actually 
divide it, contraction-waves will pass throughout 
the whole mass. But this very reasonable hypo- 
thesis of the contraction-waves in the Medusz 
being possibly nothing more than muscle-waves is 
negatived by other facts, which I shall now proceed 
to state. 
In the first place, if a number of experiments be 
tried in any of the three modes of section above 
described, it will be found that extreme variations 
are manifested as regards the degree of tolerance. 
In the spiral mode of section, for instance, it will 
sometimes happen that the contraction-wave will 
become blocked when the contractile strip is only 
an inch long, while in other cases (as in the one 
represented) the wave will continue to pass through 
a strip more than thirty times that length; and 
between these two extremes there are all possible 
grades of tolerance. Now it seems to me that if 
the tissue through which these contraction-waves 
pass 1s supposed (as far as they are concerned) to be 
of a functionally homogeneous nature, no reason 
can be assigned why there should be such great 
differences in the endurance of the tissue in different 
individual cases; while, if we suppose that the 
passage of the contraction-waves is more or less 
dependent on the functional activity of the nervous 
plexus which we know from microscopical examina- 
tion to be present, we encounter no such difficulty ; 
for it is almost to be expected that in some cases it 
would happen that important nerves would soon be 
encountered by the section, while in other cases it 
