ME, Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAE. 
725 
or not an anaesthetic, will do the same. That nitrite of amyl, caffein, &c. should do so, 
one would not be very surprised to hear; but it would scarcely be expected that 
strychnine, for instance, should block contractile waves ; yet it does so even in doses 
so small as only just to taste bitter. Nay, even fresh water completely blocks contractile 
waves after the strip has been exposed to its influence for about half an hour, and exerts 
a permanently slowing effect after the tissue is restored to sea-water. These facts show 
the extreme sensitiveness of the nervo-muscular tissues of the Medusae to any change in 
the character of their surrounding medium — a sensitiveness which we shall again have 
occasion to comment upon when treating of the effects of poisons. 
( i ) In conclusion, I may mention an interesting fact which is probably connected with 
the summation of stimuli before explained. When a contractile strip is allowed to rest 
•for a minute or more, and a wave is then made to traverse it, careful observation will show 
that the passage of this wave is slower than that of its successor, provided the latter 
follows the former after not too great an interval of time. The difference, however, is 
exceedingly slight, so that to render it apparent at all the longest possible strips must 
be used ; and even then the experimenter may fail to detect the difference, unless he 
has been accustomed to signalling, by which method all these observations on rate have 
to be made. 
(B) Stimulus-waves. — (a) The rate of transmission of tentacular waves is only one 
half that of contractile waves, viz. 9 inches a second. This fact appeared to me very 
remarkable, in view of the consideration that the tentacular wave is the optical expres- 
sion of a stimulus-wave, and that there can be no conceivable use in a stimulus- 
wave being able to pass through contractile tissue independently of a contractile 
wave, unless the former is able to travel more rapidly than the latter ; for the only 
conceivable use of the stimulus-wave is to establish physiological harmony between 
different parts of the organism ; and if this wave cannot travel more rapidly than a 
contractile wave which starts from the same point, it would clearly fail to perform this 
function. 
In view of this anomaly I was led to think that if the rate of the stimulus-wave 
is dependent in a large degree on the strength of the stimulus that starts it, the slow 
rate of 9 inches a second might be more than doubled, if, instead of using a stimulus 
so gentle as not to start a contractile wave, I used a stimulus sufficiently strong to do 
this. Accordingly I chose a specimen of Aurelia wherein the occurrence of tentacular 
waves was very conspicuous, and found, as I had hoped, that every time I stimulated 
too gently to start a contractile wave, the tentacular wave travelled only at the rate of 
9 inches a second, whereas if I stimulated with greater intensity I could always observe 
the tentacular wave coursing an inch or two in front of the contractile wave. 
(b) It is remarkable, however, that in this, as in all the other specimens of Aurelia 
which I experimented upon, the reflex response of the polypite was equally long whatever 
strength of stimulus I applied to the swimming-bell ; or, at any rate, the time was only 
slightly less when a contractile wave had passed than when only a tentacular wave had 
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