208 JELLY-FISH, STAR-FISH, AND SEA-URCHINS, 
of the facts cannot, I think, be disputed; and it 
fully explains why, in the unmutilated animal, the 
degree of elongation on the part of the manubrium 
usually exhibits an inverse proportion to the degree 
of locomotor activity displayed by the bell. I may 
here state that I have also observed indications of 
muscular tonus in some of the other Meduse, but 
for the sake of brevity I shall now restrict myself 
to the consideration of this one case. 
To my mind, then, it is an interesting fact that 
ganglionic tissue, where it can first be shown to 
occur in the animal kingdom, has for one of its 
functions the maintenance of muscular tonus; but 
it is not on this account that I now wish to draw 
prominent attention to the fact before us. Physio- 
logists are almost unanimous in regarding muscular 
tonus as a kind of gentle tetanus due to a persistent 
ganglionic stimulation, and against this opinion it 
seems impossible to urge any valid objection. But, 
in accordance with the accepted theory of gan- 
glionic action, physiologists further suppose that the 
only reason why some muscles are thrown into a 
state of tonus by ganglionic stimulation, while other 
muscles are thrown into a state of rhythmic action 
by the same means, is because the resistance to the 
passage of the stimulation from the ganglion to 
the muscle is less in the former than in the latter 
case. Here, be it remembered, we are in the 
domain of pure speculation: there is no experi- 
mental evidence to show that such a state of 
differential resistance as the theory requires actu- 
ally obtains. Hence we are quite at liberty to 
