SECTION OF NAKED-EYED MEDUSA, 127 
manifest a power of penetration to which the 
normal contractions of the tissues in which it occurs 
bear so small a proportion; why it is that the con- 
tractile tissues should be so deficient in the power of 
originating a spasm, even in response to the strongest 
stimulation applied to themselves ;—these and other 
questions at once suggest themselves as questions of 
interest. At present, however, I am wholly unable 
to answer them; though we may, I think, fairly 
assume that it is the ganglionic element in the 
margin, and probably also in the radial tubes, 
which responds to direct stimulation by discharging 
a peculiar impulse, which has the remarkable effect 
in question. For the sake of rendering the matter 
quite clear, let us employ a somewhat far-fetched 
but convenient metaphor. We may compare the 
general contractile tissues of this Medusa to a mass 
of gun-cotton, which responds to ignition (direct 
stimulation) by burning with a quiet flame, but to 
detonation (marginal stimulation) with an explosion. 
In the tissue, as in the cotton, every fibre appears 
to be endowed with the capacity of liberating 
energy in either of two very different ways; and 
whenever one part of the mass is made, by the ap- 
propriate stimulus, to liberate its energy in one of 
these two ways, all other parts of the mass do the 
same, and this no matter how far through the 
mass the liberating process may have to extend. 
Now, employing this metaphor, what we find is 
that, while the contractile fibres resemble the cotton 
fibres in the respects just mentioned, the ganglion 
cells resemble detonators, when themselves directly 
