NERVOUS TRANSMISSION IN THE ACTINIANS 89 



4. 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 the 

 tongue will again call forth a retraction of the oral disc. 



5. If a tongue of tissue is cut equatorially from the co'umn so 

 as to girdle it for half its circumference, and a stimulus is ap- 

 plied to the free end of the tongue, such stimulus is only occa- 

 sionally followed by a retraction of the disc, showing that this 

 least sensitive part of the column is not in free nervous con- 

 nection horizontally with the rest of the column. 



6. If the pedal edge of the column is cut off by an incision 

 parallel to this edge and about 3 mm. inside it, thus producing 



Fig. 1 Side view of a Metridium from which a lateral tongue of tissue has 

 been cut (Experiment 3) ; X, region of stimulation. 



a band of tissue 4 to 5 cm. long and attached by an end only 

 to the animal (fig. 2), a mechanical stimulus applied to the 

 free end {X) of this band is followed immediately by the retrac- 

 tion of the oral disc. If this band is anywhere completely cut 

 across, a stimulus distal to the cut is never followed by a re- 

 sponse of the disc even though the two faces of the cut are in 

 contact. 



7. If a Metridium is cut through vertically so as to separate it 

 completely into two parts except for the pedal disc, the stimula- 

 tion of one part is followed by a retraction of the halves of the 

 oral disc in both parts, showing that the pedal disc is a means 

 of transverse nervous connection for the animal. 



