ME. Gr. J. BOMAHES ON THE LOCOMOTOE SYSTEM OF MEDUSA. 
721 
In such experiments it generally happens, as here represented, that reducing the width 
of a circular strip by one half produces no effect, or only a slight effect, on the rate, 
while further narrowing to the degree mentioned produces a conspicuous effect. I may 
also state that when, as occasionally happens, the immediate effect of narrowing a 
circular strip to one half is to temporarily block the contractile waves, when the latter 
again force their passage, their rate is slower than it was before. It seems as if the 
more pervious tissue-tracts having been destroyed by the section, the less pervious ones, 
though still able to convey the contractile wave, are not able to convey it so rapidly as 
were the more pervious tracts. 
(e) In order to ascertain whether certain zones of the circular contractile sheet in all 
individuals habitually convey more of the contractile influence than do other zones, I 
tried a number of experiments in the following form of section. Having made a cir- 
Fig. 11. 
cular strip, I removed the lithocysts and then cut the strip as represented in fig. 11. 
On now stimulating the end a, the resulting contractile wave w'ould bifurcate at b, and 
then pass on as two separate waves through the zones be, b d. Now, as these two waves 
were started at the same instant of time, they ran, as it were, a race in the two zones 
and in this way the eye could judge with perfect ease which wave occupied the shortest 
time in reaching its destination. This experiment could be varied by again bisecting 
each of these two zones, thus making four zones in all, and four waves to run in each 
race. A number of experiments of this kind showed me that there is no constancy in 
the relative conductivity of the same zones in different individuals. In some instances 
the waves occupy less time in passing through the zone be than in passing through 
the zone b d ; in other instances the time in the two zones is equal ; and, lastly, the 
converse of the first-mentioned case is of equally frequent occurrence. Very often 
the waves become blocked in b c while they continue to pass in b d, and vice versa. Now 
all these various cases are what we might expect to occur, in view of the variable 
points at which contractile waves become blocked in spiral strips See. ; for if the con- 
tractile tissues are not functionally homogenous, and if the relatively pervious conductile 
tracts are not constant as to their position in different individuals, the results I have 
just described are the only ones that could be yielded by the experiments in question. 
Considering, however, that in these experiments the central zones are not so long as the 
