858 AUSTR\LIAN HIRUDINEA, II , 



The anterior sucker occupies dorsally six annuli, the sixth 

 creeping across to form the posterior lip. The posterior sucker 

 differs very slightly in diameter from the rest of the body, and 

 is set on it obliquely. 



There are three pairs of eyes situated on annuli 1, 3, and 6 

 respectively. 



The male genital aperture lies in the midline in the posterior 

 region of the 37th annulus, that is the 32nd postoral ring, or 2nd 

 annulus of somite x., the usual position for it in Arhynchob- 

 dellids; its aperture is transversely elongated, and provided with 

 prominent tumid lips. The female genital aperture lies in the 

 midline on the 42nd annulus, that is, the 37th postoral ring, in 

 the 2nd annulus of somite xi. 



The anus is situated between the fourth and fifth annuli from 

 the posterior end. 



Digestive system. — The mouth-cavity is very wide, measuring 

 about one-third of the body. The pharynx measures about one- 

 third of the body. In transverse section it has the shape of an 

 equilateral triangle with the apex in the dorsal median line. 

 There is a slight groove at each angle, and the sides of the 

 pharynx are convex towards the outer surface of the body. The 

 wall has the same characters as in other Arhynchobdellids, con- 

 sisting of (a) epithelium; (b) longitudinal muscle-fibres, about 

 five fibres in each row; (c) radial muscle-fibres; (d) circular 

 muscle-fibres, arranged so as to form a circle circumscribing the 

 triangular pharynx, and passing through the apices so that (b) 

 and (c) form plano-convex masses between the epithelium and 

 the circular musculature. The portion of the pharynx between 

 the genital apertures becomes elliptical in shape, the long axis 

 being directed in a dorsoventral line. 



In the region of the female genital aperture there appears in 

 the pharynx a peculiar proboscis-like organ. It has a triangular 

 shape, and extends, as such, through about one somite before 

 passing into the oesophagus at the end of the pharynx. The wall 

 of this structure consists of (1) an internal epithelium of columnar 

 cells, very much folded, and sending long projections into the 



