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). 
Fia. 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. Cerianthus 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 
with 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 
5 
