DESCRIPTIONS OF FOUR DISTOMES. 27 



portion of the cirrus-sac and is continued in a short pars prostatica. The cirrus which 

 follows is a large organ, about 0.4 millimetre in length, and occupies more than half of 

 the cirrus-sac. 



The ovary (PL IV, Fig. 3) is an ovoid body about 0.26 millimetre in length and 

 lies partly behind and partly dorsal to the acetabulum and a little to the right of this 

 organ. It is immediately beneath the dorsal body-wall. The oviduct is a short 

 canal which leaves the left side of the ovary and passes to the ootyp; it is entirely 

 surrounded by the shell-gland. A receptaculum seminis is wanting. Laurer's 

 canal, which is present in the form of a delicate tube, passes from the ootyp near 

 the median line first to the right towards the ovary, then dorsally and posteriorly 

 to the external opening, which is to the right of the median line. The yolk-glands 

 consist of about forty rounded or elongated bodies on each side. They lie just 

 beneath the ventral body-wall and immediately ventral to the intestinal cseca and 

 extend from the posterior end of the testes forward a short distance anterior to the 

 acetabulum. They are thus lateral in position and occupy about the middle third 

 of the body. Five or six ducts arise from each yolk-gland at different regions and pro- 

 ceed dorsally to a common point, where they unite to form the transverse yolk-duct. 

 These two vessels, which are dorsal in position, meet in the midst of the shell-gland in 

 the median line, and form a very short median yolk-duct which joins the ootyp. The 

 shell-gland is a rather extensive group of glandular cells that lie against the dorsal 

 body-wall to the left of the ovary with which they are in contact. It encloses the 

 oviduct, Laurer's canal, the transverse and median yolk-ducts, and the beginning 

 of the uterus. This last-named organ is not very voluminous and consists of a 

 descending and an ascending limb. The former passes posteriorly with a serpen- 

 tine course to within a short distance of the hinder end of the body; the latter 

 passes in a similar way to a point dorsal to the acetabulum and near the posterior 

 end of the cirrus-sac. From this point it passes diagonally alongside the cirrus- 

 sac to the genital pore on the left side of the body. The diameter of the two limbs 

 is the same in young worms, but in the older and larger ones the ascending limb is 

 much the larger and may become a third as wide as the body itself posterior to the 

 testes. It is filled with a dense mass of dark-colored eggs. The egg measures 0.03 

 millimetre by 0.019 millimetre. A metraterm is not developed. 



The following is a specific diagnosis of Renifer ellipticus: Small, elliptical, semi- 

 cylindrical worms averaging 4 millimetres in length and 1.4 millimetres in breadth. 

 Oral sucker subterminal, 0.35 millimetre in diameter; acetabulum 0.41 millimetre 

 in diameter, sessile, about 0.73 millimetre from the oral sucker. Body covered with 

 minute scales. Pharynx and oesophagus of moderate size; intestinal caeca extend 



