THE FEMALE ORGANS. 39 



c. The vesicula seminalis is an elongated sac lying 



above, and somewhat in front of, the ventral 

 sucker. 



d. The ductus ejaculatorius is a fine tube running 



from the vesicula seminalis to the end of the 

 penis. When the penis is withdrawn this duct 

 is thrown into convolutions. 



e. The penis or ' cirrus ' is a large muscular organ 



which lies, when withdrawn, within the cirrus- 

 sac, a space in front of the ventral sucker. It 

 can be protruded by evagination, and the ejacu- 

 latory duct then lies within it. 



f. The cirrus-sac is a cavity between the ventral sucker 



and the genital aperture. The penis lies in it 

 when withdrawn, as do also the vesicula seminalis 

 and a small accessory gland which surrounds the 

 ejaculatory duct. 



2. The female organs. 



a. The ovary is branched and tubular : it lies on the 



right, or rarely on the left side in front of the 

 anterior testis, and its branches unite to form 

 the narrow ovarian duct. 



b. The yolk-glands are very numerous small rounded 



masses, scattered along two areas extending 

 along the sides of the body from end to end, 

 and each nearly one quarter of the whole width 

 of the animal. 



c. The vitellarian ducts, or ducts of the yolk-glands, 



unite to form an anterior and a posterior duct 

 on each side. These unite about the junction 

 of the anterior and middle thirds of the animal, 

 forming a transverse duct, which runs inwards 

 to open into the median yolk-reservoir : from 

 this a single median vitellarian duct runs a short 

 distance forwards and unites with the ovarian 

 duct to form the oviduct. 



