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the zigzag course of the dotted line. Yet in the case of healthy specimens the 
spontaneous contractions are apparently as synchronous over the entire extent of the 
nectocalyx as they are when this organ is in an unmutilated state. Further, if the 
extreme margin of the nectocalyx be now removed, the paralyzed organ will respond to 
stimuli applied at any point just as readily and as simultaneously over its whole extent 
as it would do were there no system of interdigitating cuts present. 
(5) The other mode of section to which I have alluded is that of a simple spiral. 
If the margin of Sarsia be removed in the form of a continuous thread with one end 
attached to the nectocalyx (as already described in the case of Staurophora laciniata ), 
and if the section be then continued in the form of a spiral having two or more turns 
from the base to the apex of the cone, a wave of contraction, starting from any point in 
the original margin of the animal, passes into the spiral upon reaching its point of 
origin, and then runs round and round the spiral from the base to the apex of the cone. 
In vigorous specimens the course of the contractile wave is so rapid that, in a spiral of 
one turn, it requires a quick eye to perceive its true nature : to most persons the con- 
traction appears simultaneous over the entire spiral, whereas it is really a successive 
wave. But in the case of non-vigorous specimens, or of a spiral having two turns, even 
a slow eye may perceive the true nature of the contraction. Some specimens of Sarsia 
endure more turns of the spiral than do others ; but in all cases the animal will live 
for a long time in this corkscrew-like shape, performing its spontaneous contractions as 
pertinaciously as ever. As might be expected from the analogy of the experiment last 
described, if the marginal centres be removed altogether, the paralyzed spiral will 
respond to the weakest stimulus applied at its lower end or any other part of its 
course, and this as vigorously as if no spiral section had been performed. I may here 
observe, in passing, that of all the experiments upon excitable tissues with which I am 
acquainted, there is no single instance of a series of contrasts so astounding as are those 
exhibited by Sarsia — first darting hither and thither with the greatest spontaneity and 
vigour, then reduced to a state of absolute quiescence by the removal of an intensely 
localized system of locomotor centres, but yet remaining so keenly sensitive to stimu- 
lation throughout its entire extent, as shown by the modes of section just described. 
( c ) The gonocalyces of the covered-eyed Medusae, being of a much larger size than 
are the nectocalyces of the naked-eyed Medusae, present much greater facilities for 
conducting experiments in section. Of the species of the covered-eyed Medusae which I 
have had the opportunity of examining, Aurelia aurita, on account of its flat shape, is 
much the best suited for this line of inquiry. I have therefore made this species the 
subject of a very extensive investigation. Under the present heading, however, it will 
only be necessary for me to describe three observations. 
As already stated, the concentration of locomotor centres into the lithocysts of this 
species is more marked than in the case of any other species I have met with, notwith- 
standing individual instances frequently occur in which feeble locomotor centres are also 
scattered through the general contractile tissue of the gonocalyx. It will happen, then, 
