DESCRIPTIONS OF FOUR DISTOMES. 35 



left of the posterior end of the pharynx. The excretory pore is at the posterior end 

 of the body. 



The digestive tract is made up of pharynx and intestinal caeca. The former is 

 0.19 millimetre in length and 0.13 millimetre in width. There is no oesophagus. The 

 intestinal caeca are wide tubes, without lateral projections, which reach into the 

 posterior extremity of the body. The average width of each is 0.16 millimetre. 



The excretory vesicle is Y-shaped, with a very long median portion and short 

 crura. The former extends from the excretory pore forward to the region of the 

 ovary and shell-gland. Its course lies close to the ventral body-wall as far as 

 the posterior testis; it then winds between the testes, near the centre of the body, 

 and passes to the left of the receptaculum seminis and ovary. The excretory crura 

 extend forward, one on each side of the body, parallel and dorsal to the intestinal 

 caeca. They terminate near the anterior ends of the yolk-glands. The diameter of 

 the median portion is about 0.1 millimetre; that of the crus is about 0.07 milli- 

 metre. 



The testes are two large, ovoid, but somewhat irregular organs situated near the 

 middle of the body. Each testis measures about 1.14 millimetres in length and 0.8 

 millimetre in width. In thickness they measure about 0.32 millimetre and entirely 

 fill the body of the worm between the dorsal and ventral body-walls. The testes are 

 situated one diagonally behind the other, the anterior testis being on the right side 

 of the body. The vas efferens from the anterior testis leaves its anterior border and 

 passes forward between the receptaculum and the ovary, ventrally to the former 

 and dorsally to the anterior end of the latter. The vas efferens from the posterior 

 testis passes to the left of the anterior testis and of the receptaculum seminis, and 

 meets its fellow near the anterior end of the ovary. The vas deferens, which is 

 formed by their union, runs forward between the intestinal caeca to the genital pore, 

 enclosed the entire distance in a cirrus-sac. The greater portion of the vas deferens 

 functions as a vesicula seminalis. This organ is thus very long, and is still further 

 increased in length by its serpentine course. It is also very broad, having an average 

 width of 0.06 millimetre, and is constantly filled with spermatozoa. The anterior 

 end of the vas deferens forms a short cirrus, which can be protruded from the body. 

 The cirrus-sac is peculiar because of its great length, and also from, the fact that it is 

 almost entirely filled by the voluminous vesicula seminalis. The posterior portion 

 of that organ, in fact, exactly fills the cirrus-sac; its anterior portion, however, has 

 a slightly smaller diameter, and leaves a small space within the cirrus-sac. 



The ovary (PL IV, Fig. 7) is an elongated body which lies in front of the recep- 

 taculum seminis and the testes and just behind the acetabulum. It has a length 



