140 NATURAL HISTORY OF 



pedal disc is furrowed, the furrows having a distinct 

 relation to the arrangement of the septa. 



The tentacles are hollow and are prolongations of 

 the body cavity. Their number bears a distinct rela- 

 tion to the interseptal and intraseptal chambers (i.e. 

 the segments into which the body cavity is divided by 

 the principal and secondary septa). They are perfo- 

 rated at the tip, and can be opened and closed at the 

 will of the animal, being supplied near the orifice with 

 a sphincter muscle. Many species are able to extend 

 individual tentacles to a considerable distance. 



The mouth is a simple longitudinal opening in the 

 centre of the oral disc, and forms the entrance to the 

 oesophagus. There are two lip-like folds, one on each 

 side of the mouth. The shape of the mouth enables 

 the body to be described with reference to it, two axes 

 being clearly defined, the sagittal axis running in the 

 direction of the mouth and the transverse axis at right 

 angles to it. The oesophagus (ces) or, as some observers 

 have called it, the stomach, is marked with fui-rows or 

 grooves running from top to bottom, those which pro- 

 ceed from the angles of the mouth being larger and 

 deeper, and generally passing near the gastric orifice 

 into lappets which hang down from the base of the 

 oesophagus. These larger grooves are always open 

 and richly ciliated, and are called " gonidial grooves." 

 Some observers have detected coloured masses in the 

 walls of the oesophagus, which they suspect to have a 

 biliary action. 



The septa, as before described, divide the body 

 cavity into distinct segments. The usual arrangement 

 amongst the Zoantharia is hexameral (i.e. that there 

 are six primary septa). In most cases also there are 



