SECTION OF COVERED-EYED MEDUSA. 91 
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 ex- 
periment 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 in- 
stances, the waves occupy less time in passing 
through the zone be than in passing through the 
zone 6 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 occur- 
rence. Very often the waves become blocked in 
b ce, 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 contraction-waves become blocked 
in spiral strips, ete.; for if the contractile tissues 
are not functionally homogeneous, and if the rela- 
tively 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 peripheral 
zones, I think it may fairly be said that the con- 
ductile power of the latter is greater than that of 
the former; for, otherwise, the above experiments 
ought to yield a large majority of races won by the 
