Introduction to Anwial Morphology. 195 



anteriorly (excretory or auditory r). Beside it there is 

 occasionally a closed vesicle containing neither solid 

 matter nor clear cells. 



The mouth is ventral, only anterior and terminal 

 in Floscularia and Stephanoceros ; it opens into a 

 muscular, often bulbous, non-ciliated pharynx, contain- 

 ing the horizontally acting, semi-lunar, or horn-like 

 jaws. These consist of two parts : a lower jaw (incus) 

 made of a fulcrum and two movable rami, and an 

 upper jaw (malleus) made of a handle and a toothed 

 blade or uncus. Muscles are attached to chitinous 

 ridges on these. Sometimes a reserve pair of jaws 

 lies beside the functional pair. The oesophagus is short, 

 the stomach large, ciliated, lined by coloured hepatic 

 •cells, and receiving the secretion of a pair of rounded 

 (pancreatic r) glands ; it may be blind, with ciliated 

 cardiac caeca, or may end in a straight intestine with 

 a dorsal anus. There is no circulatory nor respiratory 

 apparatus ; the clear or faintly reddish chyle moves 

 freely in the body cavity. The water-vascular system, 

 well marked in Limnias and Floscularia, consists of 

 two long, often convoluted, canals, with cellular, ci- 

 liated walls, and short side branches or ovate vesicles, 

 each with a single, central, basal filament. These have 

 tubular or funnel-shaped openings into the body 

 cavity. The two stems unite in a contractile vesicle, 

 ending in the cloaca, or where there is no cloaca, 

 opening directly behind. In embryos there exists in 

 front of the cloaca a cellular organ, disappearing in 

 after development (primitive kidney oi Leydig ?) 



The hinder end is elongated into a short or long, 

 closely ringed or clearly jointed tail, which may be 

 either a trace of metameral growth or made of two 



O 2 



