748 
ME. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDHSiE. 
case is of less than minimal intensity, is able at the top of a staircase to give rise to a 
contraction of very nearly maximum intensity. This latter fact proves that the stair- 
case action is, at any rate in part, dependent on the process of stimulation as distin- 
guished from that of contraction. Moreover, that the effect is one pervading the 
whole extent of the irritable tissues, is proved by another fact, viz. that when at any 
stage during the construction of a staircase the electrodes are suddenly shifted to any 
other part of the irritable tissues, the next contraction will rank as the next step in 
the staircase. Other experiments have conclusively proved that the staircase action 
obtains in the case of the natural ganglionic stimulation in exactly the same way, both 
quantitatively and qualitatively, as it does in the case of artificial stimulation. 
The excitable tissues of Aurelia may be thrown into tetanus by means of strong 
faradaic stimulation. That the tetanus is due to summation of contractions may be proved 
by throwing in single shocks at one end of a spiral strip with a key, and observing that 
if the shocks are thrown in with a certain rapidity, the resulting contractile waves overlap 
one another, so giving rise to persistent spasm. In such experiments, however long the 
strip may be, and however complicated the time relations between successive stimuli are 
made, whatever disturbances are set up at one end of the strip are faithfully trans- 
mitted to the other. 
Reflex action has been proved to occur in various species of Medusse. In Sarsia 
definite nervous connexions of constant occurrence have been shown to exist between 
the tentacles, but not between the tentacles and the polypite. Section of the nervo- 
muscular sheet proves that in the case of this genus physiological harmony may, as a 
rule, be easily destroyed, although it occasionally happens that such is not the case. 
In Tiaropsis indicans the pointing action of the polypite is manifested by a portion 
of any size which may be cut from that organ. The ganglionic or localizing function 
is therefore diffused throughout the tenuous contractile tissues of the latter. This 
function admits of being destroyed, as regards any portion of the bell, by introducing 
a short incision between that portion and the base of the polypite ; but after this 
the polypite, though no longer able to localize the seat of irritation, continues able 
to perceive that a stimulus is being applied in the bell somewhere. This shows that 
while the connexions on which the localizing function depend are radial, there are other 
connexions between the bell and polypite which are not radial. The latter connexions 
will endure a considerable amount of section before they are destroyed, particularly in 
the case of the tracts occupied by radial tubes. On carrying a spiral incision three 
fourths of the way round the nectocalyx, so as to leave one radial tube intact, and on 
then irritating any part of the spiral strip, it may be observed that the polypite usually 
points to the unsevered radial tube. 
The spasmodic movements of Staurophora laciniata usually occur only when either 
the margin or the radial tubes are irritated. Although in this species ordinary contrac- 
tile waves are easily blocked by section, spasmodic waves will continue to pass after very 
severe forms of section. Now it is a remarkable thing that the contractile tissues, 
