S88 JrLLY-FISH, STAR-FISH, AND SEA-URCHINS, 
that the best form of strip to use for the purpose of 
ascertaining the maximunv rate is one which I shall 
eall the circular strip. A circular strip is obtained 
by first cutting out the central bodies (7.e. manu- 
brium and ovaries), and then, with a single radial 
cut, converting the animal from the form of an 
open ring to that of a continuous band. I dis- 
tinguish this by the name “ circular” band or strip, 
because the two ends tend to preserve their original 
relative positions, so giving the strip more or less of 
a circular form. Such a strip has the advantage 
of presenting all the contractile tissue of the 
swimming-bell in one continuous band of the 
greatest possible width, and is therefore the form 
of strip that yields the maximum rate at which 
contraction-waves are able to pass. The reason 
why the maximum rate should be the one sought 
for is because this is the rate which must most 
nearly approximate the natural rate of contraction- 
waves in the unmutilated animal. This rate,at the 
temperature of the sea and with vigorous specimens, 
I find to be eighteen inches per second. 
In a circular strip the rate of the waves is uniform 
over the whole extent of the strip; so that the time 
of their transit from one point to another varies 
directly as the length of the strip. But on now 
narrowing such a strip, although the rate is thus 
slowed, the relation between the narrowing and the 
slowing is not nearly so precise as to admit of our 
saying that the rate varies inversely as the width. 
The following figure will serve to show the propor- 
tional extent to which the passage of contraction- 
