COELENTERATA 



65 



or the rocks, the other end free. The mouth is an elongated 

 slit in the middle of the peristome or free end, it is surrounded 

 by several rows of tentacles (Fig. 44). At the ends of the 

 elongated mouth are special grooves which are continued down 

 the oesophagus and are lined with especially long cilia (Fig. 46). 



Fig. 44. Colony of sea-anemones {Sagartia parasitica) on shell of hermit crab. 



"When the mouth is closed the central parts are in apposition, 

 but the grooves, called Siphonoglyphs, remain always open, and 

 through them a current of water may be kept circulating in 

 and out of the animal even when it is in its most contracted 

 condition. Gerianthus has only one siphonoglyph. The oeso- 

 phagus ends with a free edge, and never reaches the base of 

 the sea-anemone. 



The mesenteries are vertical radial partitions which extend 

 from the peristome to the base. The outer edge is continuous 

 vnth the inner side of the body-wall. The inner edge in the 

 primary mesenteries is divided into two parts (Fig. 45). The 

 part nearest the peristome is continuous with the outside of the 

 oesophagus, but below the lower edge of the oesophagus the inner 



