26 DESCRIPTIONS OF FOUR DISTOMES. 



forming thus a semicircle. The body of the worm is widest at about its middle, from 

 which region it tapers towards both ends. These are rounded and blunt, the posterior 

 end being, however, less so than the anterior end. The length of the worm varies 

 from 3 millimetres to 4.2 millimetres, its breadth from 1.1 millimetres to 1.6 millime- 

 tres, its greatest thickness 0.8 millimetre. The entire body is thickly covered with 

 minute scales, set in transverse rows, except towards the hinder end, where their 

 arrangement is irregular. The suckers are of good size and are sessile. The oral 

 sucker is subterminal, with a diameter of 0.35 millimetre. The acetabulum is situ- 

 ated almost in the centre of the body, but somewhat nearer the anterior than the poste- 

 rior end and is 0.73 millimetre from the oral sucker in a small worm. It is 

 larger than the oral sucker, measuring 0.41 millimetre in diameter. The genital pore 

 is about half-way between the two suckers, although slightly nearer the anterior 

 one, and is very near the left edge of the body, being 0.07 millimetre from that edge, 

 and in the ventral surface. The excretory pore is at the posterior end of the body. 



The digestive tract is made up of pharynx, oesophagus, and intestinal cseca. 

 The pharynx has a length of 0.10 millimetre and the oesophagus is of moderate 

 length and measures 0.24 millimetre; both are surrounded by gland-cells. The 

 intestinal ca?ca are simple tubes without lateral branches; their width is about 0.2 

 millimetre. They extend about to the middle of the body, reaching the middle or 

 posterior portions of the testes, and being somewhat longer in the larger specimens 

 than in the smaller ones. 



The excretory vesicle is unusually long and voluminous. It is a Y-shaped tube 

 with such delicate walls that it can be traced only in sections. The median portion 

 is very long and wide. It extends forward as far as the ovary, lying dorsal to the 

 uterus and between the testes. Its width in the posterior portion of the body be- 

 hind the testes is about 0.5 millimetre, and it here occupies a quarter or more of the 

 space within the body walls. The excretory crura are also wide and extend for- 

 ward, one on each side of the acetabulum, to a position a little in front of the yolk- 

 glands. Their width is about 0.17 millimetre. 



The testes are two slightly lobate bodies situated side by side near the centre 

 of the body. They measure about 0.3 millimetre in length and width and 0.4 milli- 

 metre in thickness. The right testis is a trifle in advance of the left one. The vasa 

 efferentia pass forward to a position just dorsal to the anterior edge of the acetabulum, 

 where they unite to form the vesicula seminalis. This organ, together with the pros- 

 tate gland and the cirrus, is enclosed in a large cirrus-sac, which measures 0.8 milli- 

 metre in length and 0.19 millimetre in width, and passes diagonally across the body 

 to the genital pore at the left. The vesicula seminalis bends on itself in the posterior 



