Section IV., 1914. 187] Trans. R.S.C. 



The Beaver Fluke, Amphistomum Subtriquetrum, Rudolphi. 



By Dorothy Duff, B.A., Zoological Laboratory, McGill 

 University. 



Presented by Dr. A. Willey, F.R.S.C. 

 (Read May 26, 1914.) 



The first careful study of the anatomical and histological fea- 

 tures of Amphistomum subtriquetrum is in the Inaugural Dissertation 

 of Dr. Richard Otto. (1) As far as I can ascertain no mention has 

 been made of the occurrence of a Trematode parasite in the American 

 beaver {Castor Canadensis) prior to a notice by Dr. Willey (2) in 1912. 

 The specimens here described were taken by him from various beavers 

 trapped in the spring of 1912 and of 1913 in the Provinces of Quebec 

 and Ontario. The worms were killed in sublimate and preserved in 

 alcohol. Sections were studied which were made in three directions, 

 transverse, sagittal and horizontal. These were for the most part 

 stained with Haematoxylin and Orange G ; but staining with Haemalum 

 and Eosin was also tried. The latter combination brought out the 

 layer of subcuticular cells and other remarkable elements such as 

 certain large cells of the parenchyma and of the suckers particularly 

 well. The xylol-paraffin method was found to be the most successful 

 for embedding and sectioning. 



Rudolphi (3) is the first author to record the Trematode parasite 

 from the European beaver {Castor fiber) which he named Amphistoma 

 subtriquetrum in 1814. In 1817 Bojanus (4) reported the same Trema- 

 tode from the beaver and called it Distoma amphistomoides. In 1819 

 Rudolphi (5) described the parasite in his Entozoorum Synopsis. 

 He diagnosed it as an "Amphistoma with slightly flattened body 

 increasing in circumference towards the posterior end; with round 

 pores, a small anterior and a large posterior; Habitat, caecum and colon 

 of Castor fiber." Further in the same work (p. 360) he writes: "The 

 worm is whitish, two or three times longer than its diameter, the 

 anterior pore is terminal, the posterior, situated a quarter of the body 

 length from the caudal extremity, is very deep and wide with the 

 margin of the opening turned sharply in; the back is convex even slight- 

 ly keeled in specimens that have been long preserved, the abdomen 

 is flattened, hence the name subtriquetrum. In his description Rudolphi 

 confirms the internal features noted by Bojanus under the name 



