SECTION OF COVERKD-EYED MEDUS.^. 91 



the same instant of time, tliey 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 couUl 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 h c 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 occur- 

 rence. Very often the waves become blocked in 

 h c, while ihej continue to pass in h 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, etc. ; 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 



