32 DESCRIPTIONS OF FOUR DISTOMES. 



genital pore is about half-way between the two suckers and very nearly on the 

 median line. The excretory pore is at the posterior end of the body. 



The digestive tract consists of pharynx, oesophagus, and intestinal caeca. The 

 pharynx has a length of about 0.2 millimetre. The oesophagus is very short. The 

 intestinal cseca extend posteriorly to about the beginning of the posterior third of 

 the body. In a large worm they extend to the posterior end of the testes; in the 

 smaller one to the anterior end of those organs. They are not simple tubes, but 

 they send out short lateral projections that are most numerous and longest toward 

 their posterior ends. 



The excretory vesicle is a long Y-shaped structure, the diameter of which 

 remains approximately the same, 0.08 millimetre, throughout its entire course. The 

 median portion is very long, extending from the excretory pore forward to a point 

 just behind the shell-gland and near the anterior end of the testes, between which 

 it passes. The excretory crura are also long and extend forward to a point near the 

 pharynx. The excretory vesicle is not a simple tube, but, like the intestinal cseca, 

 it sends out short lateral projections which are especially noticeable towards its 

 anterior ends. 



The testes are two large, deeply lobate organs situated near the middle of the 

 body, and in very nearly the same transverse plane. The length and width of a 

 testis is about 0.8 millimetre, the thickness is very nearly that of the body itself. 

 The narrow space between the two testes is occupied by the median limb of the 

 excretory vesicle and the ascending and descending limbs of the uterus. The vasa 

 efferentia pass forward to a point near the anterior margin of the acetabulum, where 

 they join to form the vesicula seminalis. This is an organ of the considerable length 

 of 0.6 millimetre. It bends on itself in the cirrus-sac, and from its anterior end a pars 

 prostatica and a short cirrus extend to the genital pore. These organs are contained 

 in a cirrus-sac 0.4 millimetre in length and 0.15 millimetre in width. 



The ovary is an organ of irregularly ovoid form about 0.33 millimetre in length. 

 It lies immediately behind and to the left of the acetabulum, its anterior portion 

 lying dorsal to the ventral margin of that organ. The oviduct is a short, delicate 

 tube which passes directly from the ovary to the centre of the shell-gland. A recep- 

 taculum seminis is wanting. The shell-gland is a little behind and to the right of the 

 ovary and almost exactly in the median plane. Laurer's canal passes from the ootyp 

 dorsally and to the right, where it meets the dorsal surface to the right of the median 

 line. The yolk-glands consist of about forty rounded or elongated bodies on each 

 side. They lie mostly lateral to the intestinal cseca, and extend from the anterior 

 end of the testes to the level of the genital pore. In a small specimen they occurred 



