BEITISH ZOOPHYTES. 139 



base of the epithelial cells, and consists of nerve fibres 

 and ganglion cells, the latter giving off fibrillse from 

 the different angles. The muscular layer (m) consists 

 of flat, spindle-shaped, muscular fibrillas, generally- 

 attached to epithelial cells, which are accordingly 

 called epithelio- muscular. These muscular fibrillee are 

 strengthened by repeated pleatings. The muscular 

 layer often extends into the mesoderm. The pigment 

 granules, to which the colours of the anemones are 

 due, lie in masses below the epithelial layer. 



The mesoderm {mes) consists of layers of fibrillse 

 often closely interwoven. The mesoderm is thickest 

 in the body wall and septa, and thinnest in the tentacles. 

 Tbere are also often found connective tissue cells 

 scattered amongst the fibrilte. 



The endoderm consists of a muscular layer and a layer 

 of cylindrical epithelial cells, each armed with a single 

 flagellum. Nerve cells are found sparsely distributed. 



The muscles of the column or body wall are almost 

 always highly developed just below the oral disc, 

 where they form a muscle or sphincter, which some- 

 times enables the disc to be drawn below the upper 

 portion of the column, and so covers the tentacles. 

 The power to retract the tentacles depends on the 

 presence of a weak or strong sphincter. Some ob- 

 servers assert the presence of a special sphincter to 

 close the cardia of the oesophagus ; but others, includ- 

 ing the brothers Hertwig, deny this. The muscles of 

 the septa take different directions, those on one side 

 being transverse, those on the other longitudinal. 



The base or pedal disc is generally imperforate. In 

 some species, where the pedal disc is wanting, there 

 is an anal pore as in Cerianthus. Occasionally the 



