92 THE ELEMENTARY NERVOUS SYSTEM 



Nevertheless, when the middle of this piece is stimulated 

 mechanically or by discharging on it a small amount of 



hydrochloric acid in sea- 

 water, a withdrawal of the 

 whole oral disc follows. This 

 response ceases when all the 

 organic connections of the 

 piece with the rest of the ani- 

 mal are severed by cutting 

 through the attached mesen- 

 teries, thus allowing the piece 



Fio. 22. Metridium in whose column simplv to He ill plaC6 OH the 

 wall an oblong incision, 4 cm. by 2 cm., 



a\\:dTo1ne 9 :n?m a ai t oniyb U y t ih!re C 8 e en! sea-anemone. The cessation 

 teries. stimulus applied at x. O f reS p 0nse un der these cir- 



cumstances shows that the transmission from the surface 

 to the muscle must have been nervous and that it was not 

 due either to the mechanical effects of the contraction of 

 the piece itself on the deeper tissue, or to an accidental 

 overflow of acid. 

 Thus this experiment, 

 like the two preceding 

 ones, demonstrates a 

 direct nervous con- 

 nection between the 

 ectodermic sensory 

 apparatus of the col- 

 umn wall and the 

 longitudinal muscles 

 of the mesenteries. 



If a sea-anemone 

 is cut in two vertically in such a way that the resulting 

 halves remain attached only by the lips (Fig. 23), not 

 even the oesophagus or the oral disc remaining intact, and 



Fio. 23. Metridium cut vertically in two except 

 in the region of the lips. Stimulus applied at z. 



