Fio. 25. Metridium from which a tongue 

 running from the pedal disc to the equator 

 of the column has been cut. Stimulus ap- 

 plied at x. 



94 THE ELEMENTARY NERVOUS SYSTEM 



what would be called free nervous communication hor- 

 izontally with the rest of the column. 



If, however, a tongue of the column wall is cut from 



the pedal edge of the col- 

 umn up to its equatorial 

 region and there left in 

 organic connection with 

 the rest of the animal 

 (Fig. 25) and a mechan- 

 ical stimulus is applied to 

 the free end of this 

 tongue, a response of the 

 whole system of longitu- 

 dinal mesenterio muscles 

 commonly follows. 



If a similar tongue is 

 cut from the oral edge of the column down to its equator, 

 a stimulus applied to the free end of this tongue will again 

 call forth a retraction of 

 the oral disc. 



If the pedal edge of the 

 column is cut off by an in- 

 cision parallel to this edge 

 and about 3 millimeters 

 inside it, thus producing a 

 band of tissue 4 to 5 centi- 

 meters long and attached 

 by only one end to the ani- 

 mal (Fig. 26), a mechani- 

 cal stimulus applied to the 

 free end of this band is 

 quickly followed by the retraction of the oral disc. If this 

 band is anywhere completely cut across, a stimulus distal 



FIG. 26. AlrtriJivm, seen from the oral 

 pole, from which a portion of the pedal e Ige 

 of the column has been partly cut off. Stim- 

 ulus applied at x. 



