88 JKLLY-FISH, STAR-FISH, AND SEA-UPtCHlNS. 



that the best form of strip to use for the purpose of 

 ascertaining the inaximum rate is one which I shall 

 call the circular strip. A circular strip is obtained 

 by first cutting out the central bodies {i.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 "inaxirtiiim 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 seaand 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- 



