DICROCCELIUM LANCEATUM STILES AND HASSALL 65 



group. The mouth cavity leads into a muscular pharynx which 

 is globular and considerably smaller than the mouth sucker. Its 

 walls are composed mainly of radial muscle fibres. The pharynx 

 protrudes somewhat into the mouth cavity, thus forming an 

 upper and a lower pharyngeal lip. A protractor and a retractor 

 muscle control the forward and backward movement of the 

 pharynx. The last section of the foregut or stomadeum is the 

 oesophagus, a short and thin tube with muscular walls and an 

 inner lining formed by a cuticle with short spines directed back- 

 wards. Unicellular salivary glands situated above the oesophagus 

 open by means of long ducts into the pharynx and mouth cavity. 



The midgut or intestine into which the oesophagus opens con- 

 sists of two blind arms running backwards for a considerable 

 distance. It is lined with epithelial cells and has a rather poorly 

 developed muscular layer composed of longitudinal and circular 

 fibres. 



Excretory system. The excretory system consists of a 

 pair of canals which begin in the posterior end of the body, run 

 forward as far as the vicinity of the mouthsucker, turn more or 

 less sharply and run backward, finally uniting in a single excre- 

 tory canal. This canal occupies the median line of the posterior 

 quarter of the body and opens at the posterior end of the animal. 

 A number of smaller canals open into the two excretory canals. 

 Each of these small canals ends in a funnel closed by a so-called 

 "flame cell." The walls of the canals are formed by a thin cuticle 

 and are surrounded by the parenchyma. Inasmuch as their walls 

 have no cellular structure the canals may be regarded as remains 

 of the body cavity. The single median canal is provided with 

 longitudinal muscular fibres and a sphincter controlling the 

 excretory opening. 



Nervous system. The central nervous system consists 

 of a pair of cerebral ganglia situated above the pharynx. The 

 right and the left ganglion are connected with each other by a 

 commissure which is dorsal to the pharynx. Each ganglion 

 gives rise to three anterior and three posterior longitudinal 



