THE NEUROMUSCULAE STRUCTURE 77 



sea-anemones on which in fact some of the earliest studies 

 in these directions were made. The more typical sea- 

 anemones or actinians (Fig. 17) are cylindrical animals 

 attached by one end, the pedal disc, to a rock or other firm 

 support in the sea and carrying at the other end, the oral 



P 



FIG. 17. Diagram of a longitudinal section of the sea-anemone Metridium; the area of 

 attachment is the pedal disc p; in the middle of the oral disc o is the mouth leading into the 

 oesophagus e which opens into the digestive cavity d. The oesophagus is held in place by the 

 mesenteries m when complete c, the incomplete mesenteries i failing to reach this tube. 



disc, a cluster of tentacles in the center of which is the 

 mouth. The mouth does not open directly into the single 

 large internal space, the digestive cavity, but leads to a 

 somewhat elongated oesophagus that extends downward 

 into the interior of the actinian to the neighborhood of the 

 pedal disc, where it opens out freely into the digestive cav- 

 ity. The oesophagus, however, does not hang freely in the 



