StX'TION OF COVKUIiD-KVKI) MKDrS.E. 



89 



waves is retarded by narrowing the area through 

 which they pass : — 



Time from oiul to end of a 



circular stiip 

 Time after width has been 



reduced to one-half 

 Time after width has been 



reduced to one-quarter... 

 Time after width has been 



reduced to one-eighth ... 



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 sli. ht 

 effect, on the rate, while further narrowing to the 

 degree mentioned produces a conspicuous effect. 

 I may also state that if, as occasionally happens, the 

 immediate effect of narrowing a circular strip to one- 

 half is to temporarily block the contraction-waves, 

 when the latter again force their passage, their rate 

 is sloAver 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 contraction-wave, are not able 

 to convey it so rapidly as were the more pervious 

 tracts. 



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 circular 

 strip, I removed all the lithocysts save one, and 

 then cut the strip as represented in Fig. 14. On 



