88 THE ROYAL SOCIETY OF CANADA 



Distoma amphistomoides as follows; "Alimentary canal opening from 

 the anterior pore, a common median genital opening, the posterior 

 pore a muscular sac." Rudolphi saw no trace of nerves. 



Bojanus (6) a few years later returned to the worm, adopting 

 Rudolphi's name Amph. subtriquetrum. He now described for it 

 both longtitudinal and diagonal muscles; a bifurcated intestine with 

 blindly ending pouches (intestinal rami); and a nervous system, 

 consisting of two anteriorly placed ganglia, joined by a supra-ceso- 

 phageal commissure and giving off lateral nerve cords. He mentioned 

 also the presence of two testes, formed of radiating masses of tubes, 

 and of a coiled oviduct. 



Amph: subtriquetrum is mentioned by Laurer (7) as having a 

 layer of diagonal muscles such as he first described for Amph. conicum. 

 Dujardin (8) included it in his classification and gave the name as 

 Amphistomiim subtriquetrum, which is the accepted form now. He 

 gives some figures as to the size of the worm: length 6-75 — 15-75 

 mm. ; anterior diameter about 2 • 25 mm., posterior diameter from 4 • 5 — 

 6-75 mm. Diesing (9) also gives a brief description, summing up the 

 observations of earlier workers. 



External Features. 



The worms I have studied are covered with a smooth cuticle 

 of greyish white colour in the preserved condition. In the fresh condi- 

 tion the body is pinkish, soft and mobile. The body is well rounded 

 dorsally and flattened on the ventral surface. The diameter at its 

 anterior end averages 2 mm. which increases to 4-5 mm., measured 

 across the posterior sucker; the average length is 8 mm., this would 

 of course be greater in the living specimen. The anterior or oral 

 sucker is small and subterminal. The posterior is a very conspicuous 

 circular cavity on the ventral surface, about one third of the body 

 length from its hind end. The genital and execretory openings are 

 distinctly visible in the whole specimen. The genital pore lies in the 

 mid-ventral line a short distance behind the anterior sucker (Figs. 

 1, 2 and 7). The execretory pore is in the mid-dorsal line directly 

 over the centre of the posterior sucker (Figs. 1, 2 and 8). 



Digestive System. 



The mouth is a transverse cleft which opens directly from the 

 shallow pit of the anterior sucker into the wide pharynx. It is bounded 

 by two contiguous bundles of sphincter muscles. This characteristic 

 double sphincter is best seen in longtitudinal section (Fig 4). The 



