750 
ME. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
Aurelia in respect of the degree to which integration of its structures has advanced ; 
and, as we have seen, it likewise occupies an intermediate position in respect of the 
degree in which vicarious action of the supposed nervous elements is possible. 
Contractile waves in Aurelia aurita travel at the rate of 18 inches per second, if the 
temperature of the water is about that of the sea ; but the rate is greatly modified by 
temperature, straining, ansesthetics, and various foreign substances. Stimulus-waves 
only travel at the rate of 9 inches per second, if the stimulus which starts such a wave 
is not strong enough at the same time to start a contractile wave ; but if the stimulus 
is strong enough to start both waves, they both travel at about the same rate. 
There appears to be no further coordination among the lithocysts of the covered-eyed 
Medusae than such as arises from contractile waves coursing rapidly from one of the 
number and, as it passes the others, causing them successively to discharge ; but, in the 
case of the naked-eyed Medusae, true coordination has been proved to occur between the 
marginal ganglia, and the tracts through which it is effected have been proved to be 
the marginal nerves. Slightly cutting the margin of a naked-eyed Medusa exerts a very 
deleterious influence upon the vigour of the animal ; and violent nervous shock, 
while it always suspends both spontaneity and irritability, will sometimes also destroy 
coordination for a considerable time after spontaneity returns. 
The poisons whose effects I have described are chloroform, nitrite of amyl, caffein, 
strychnia, veratrium, digitalin, atropin, nicotin, alcohol, and cyanide of potassium. The 
details of this part of the inquiry are rendered particularly interesting from the fact that 
in the case of Sarsia we have the means of testing the comparative influence of any 
poison on the central, peripheral, and muscular systems ; but it is needless here to re- 
j>eat details. In general, it will be remembered that the effects of the various poisons 
on these respective systems are almost uniformly such as occur in the case of the higher 
animals. In one important particular, indeed, the actions of nearly all the poisons differ 
from their actions on the higher animals ; for there is no poison in the above list which 
has the property, when administered to the Medusae, of destroying life till long after it 
has destroyed all signs of irritability. I have sought to explain this apparent anomaly 
by the considerations, first, that the Medusae present to the action of the central-nerve 
poison no nerve-centres of vital importance to the organism ; and, second, that my 
method of administering the poisons to the Medusae was very different from that which 
is usually employed when administering these poisons to vertebrated animals. 
Fresh water acts as a deadly poison to the Medusae. The naked-eyed species usually 
cease their movements the instant they touch the fresh water, and are killed by it after 
an exposure of a few minutes ; but the covered-eyed species are slightly more tolerant 
of its influence. The cause of this deadly influence exerted by fresh water depends on 
the absence of sea-water, and not on the difference of density between the former and 
the latter. Chloride of sodium alone, added in appropriate amount to fresh water, de- 
prives the latter, to a very great extent, of its deleterious influence ; but this is not the 
