426 ON DIDYMORCHIS, 



The eyes are of very simple structure and resemble those of 

 Rhabdocoeles in general.* Each consists of a cup of pigment, 

 the granules of which are few, large and of regularly rounded 

 form, and an enclosed structureless body not divided into cells. 



Excretory System. 



The excretory system opens on the exterior on each side on the 

 ventral surface near the lateral margin almost opposite the 

 posterior extremity of the pharynx. The opening (exc.) leads 

 into a very narrow canal which enters a rounded mass of granular 

 material. In this the canal winds about. Eventually two main 

 canals are given off, one (a.v.) passing forwards, the other (p.v.) 

 backwards. The former soon bifurcates. Of its two branches the 

 inner soon also divides into an outer and an inner branch. The 

 outer branch of the main canal runs forwards to the region in 

 front of the eyes, where it divides into two branches, of which 

 one is continued forwards towards the anterior margin, where it 

 runs inwards and perhaps anastomoses with the corresponding 

 vessel of the opposite side, while the other runs almost directly 

 inwards and unites with the outer branch of the inner division 

 of the main anterior canal to form a short single transverse 

 vessel which passes into the corresponding vessel of the opposite 

 side. The posterior main canal soon divides into two vessels 

 which run backwards almost parallel with one another to a point 

 just behind the posterior extremity of the testis where they unite 

 to form a single transverse commissural trunk. 



Reproductive System. 



There are two compact testes (t.) of a somewhat oval shape, 

 situated close to the posterior border of the body in immediate or 

 almost immediate contact with one another posteriorly, lying 

 with their long axes directed outwards and forwards. Their 

 shape is a narrow oval, slightly curved, with the antero-internal 



* R. Hesse, " Untersuchungen iiber die Organe der Lichtempfindung bei 

 niederen Thieren." Zeitschr. wiss. Zool. 62 Bd. (1897). 



