DISTOMUM HEPATICUM 5 



occupying the middle third of the body. The branches of 

 each testis are gathered into a duct, the vas deferens, and 

 the two vasa deferentia run forward on either side of the 

 middle line as far as the ventral sucker, where they unite 

 and form a relatively large pear-shaped sac known as the 

 vesicula seminalis. From the vesicula a fine somewhat 

 convoluted tube, known as the ductus ejaculatorius, runs 

 forward to enter a stout muscular organ of cylindrical shape 

 known as the penis or cirrhus, which in its turn opens 

 at the generative pore. Normally the penis is invaginated, 

 and lies in a cavity just in front of the ventral sucker called 

 the cirrhus-sac, but it can be evaginated and protruded 

 from the generative aperture, in which case, as it is turned 

 inside out, the ductus ejaculatorius is carried up the middle 

 of it, and opens at its terminal end. (Fig. i, D.} 



The female organs comprise an ovary with its duct, and 

 certain accessory glands. The ovary, like the testis, is a 

 branched tubular organ, but, unlike the testis, it is unpaired. 

 It lies usually on the right side of the body in front of 

 the right testis and rather behind the ventral sucker. The 

 branches of the ovary unite to form a short narrow oviduct, 

 which runs towards the middle line and fuses with the 

 vitelline duct. The last named is formed by the union 

 of two transverse ducts, which convey the albuminous secre- 

 tion of the vitelline glands, situated along the entire length 

 of the right and left margins of the body. The vitelline 

 glands themselves have the form of very numerous small 

 rounded vesicles scattered over a definite area on the right 

 and left sides of the body. Each vesicle has a duct which 

 unites with the ducts of adjacent vesicles to form larger ducts, 

 and these in turn unite to form on each side of the body 

 an anterior and a posterior longitudinal collecting duct. The 

 last named unite to form the transverse duct already men- 

 tioned, and the transverse ducts join in the middle line to 

 form the common vitelline duct, which runs forward for a 

 short distance before it unites with the ovarian duct. The 

 common vitelline duct is swollen at its origin to form the 

 so-called vitelline reservoir. The ovarian and vitelline ducts 

 are surrounded at their point of union by a seemingly com- 

 pact globular glandular mass, the shell-gland, which is 

 really composed of an aggregate of minute unicellular glands. 



