714 
ME. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
of sensitiveness manifested by the radial tubes of Sarsia, Tiarojpsis indicans, &c., it 
may be suggested that if we imagine a vast number of nerve-tracts coursing from all 
parts of the bell towards the ganglionic tracts, we may imagine that on irritating 
any of these nerve-tracts near their central or ganglionic ends (nerve-trunks) a greater 
effect might be thus produced on the contractile tissues than could be produced by 
irritating the latter directly. In view of this possibility I tried making a V-shaped 
incision from the margin inwards, the angle of the V being situated about halfway 
between the centre and the circumference of the bell. The two sides of the V, however, 
did not quite meet at this angle, the effect of the section being thus almost, though not 
quite, to sever a wedge-shaped piece of tissue from the rest of the nectocalyx. Now 
on irritating the marginal tissue composing the thick end of this wedge, the latter 
went into a spasm, and, communicating the spasmodic wave through the very narrow 
tract of tissue at its thin end, it threw the whole nectocalyx into a spasm. This, of 
course, was what I expected, and from the mode of section it followed that the whole of 
the influence which caused the nectocalyx to go into a spasm must have passed through 
the narrow piece of tissue by which the wedge-shaped portion had been left in connexion 
with the rest of the nectocalyx. Yet, on waiting till the spasm passed off and then 
crushing with the forceps this narrow connecting piece of tissue, no response at all was 
given by the nectocalyx. This experiment, therefore, clearly shows that the nerve- 
trunk hypothesis will not account for the facts ; because, as the hypothesis would require 
us to suppose that the entire nerve-supply by which the spasm-causing influence was 
conveyed to the nectocalyx passed through the narrow connecting piece of tissue, 
crushing this tissue ought, according to the hypothesis, to have produced a spasm ; for 
at whatever point in the course of a nerve a stimulus is applied, the effect on the con- 
tractile tissue supplied by that nerve is the same*. 
( g ) There is one other fact Avorth stating with regard to this wedge-shaped form of 
section. Immediately after making the cuts which nearly but not quite sever the 
wedge-shaped mass, it is often observable that the shock suffered by the narrow 
connecting piece of tissue prevents it from conducting the spasmodic influence to the 
nectocalyx, the wedge itself alone going into a spasm. After a variable time, however, 
perhaps as long as a quarter of an hour, the conducting-power of the connecting-tissue 
is restored. But to produce this effect of shock, the connecting piece of tissue must be 
exceedingly narrow. 
( h ) In conclusion, I may state that anaesthetics have the effect of blocking the spas- 
modic wave in any portion of tissue that is submitted to their influence. It is always 
observable, however, that this effect is not produced till after spontaneity has been 
fully suspended, and even muscular irritability destroyed as regards direct stimulation. 
Up to this stage, the certainty and vigour of the spasm consequent on marginal irri- 
* The “avalanche” doctrine as to the summation of influence in a nerve appears to have become obsolete; 
but; even if true it might be neglected in the above considerations — the supposed nerve-length being so small and 
the contrast between the effects of central and peripheral stimulation being so great. 
