136 THE ELEMENTARY NERVOUS SYSTEM 



cordance with the arrangement of the other pairs of com- 

 plete mesenteries (Fig. 41). The grooves thus mark the 

 lines of attachment of these mesenteries and are the result 

 of the contraction of their transverse muscles, which are 

 those concerned with the opening of the oesophagus. 



If fragments of fish meat are put on the lips of a fully 

 expanded Metridium, they are carried into the animal by 



A .. B 



Fio. 41. A, outline of the sea-anemone Metridium showing on its column the vertical 

 grooves that accompany the opening of the oesophagus. B, transverse section of the same 

 sea-anemone to show the relation of the oesophagus and grooves to the pairs of complete 

 mesenteries whose transverse muscles open the oesophagus and form the grooves. 



ciliary action through an oesophagus that opens widely 

 to receive them and during this operation the column of 

 the animal is marked by the same vertical grooves that 

 were seen in the experiment with acidulated seawater. 

 As the pieces of food pass into the digestive cavity the 

 grooves fade out. It is clear, then, that the transverse 

 muscles of the complete mesenteries are concerned with 

 the expansion of the oesophagus for the reception of food. 

 If a piece of fish meat is placed upon the tentacles of 

 an expanded Metridium, these organs become character- 

 istically stimulated and if the meat is removed before it 

 is brought by the tentacles to the animal's lips, the cesoph- 



