[duff] THE BEAVER FLUKE 91 



in the position of the excretory pore. Otto figures the bladder as 

 extended into a thin tube which opens at the posterior end of the body. 

 However, he does not mention the exact position of the pore in the 

 text, and it is altogether likely that he observed it directly over the 

 sucker, which Braun (12) gives as the position throughout the genus, 

 and the appearance in the diagram is due to the difficulty of showing 

 in a flat drawing things which lie in different planes. Therefore I 

 consider that the fluke of the Canadian beaver (Castor Canadensis) 

 and that of the European beaver (Castor fiber) are one and the same 

 species, namely Amphistomum subtriquetrum. 



It is very interesting in view of the fact that the hosts differ 

 specifically to find the parasites identical in the Canadian and Euro- 

 pean beavers, and to find them occupying the same regions in the 

 intestinal tract of the host. Last autumn I noted an analogous 

 case when examining some specimens of Gammarus (apparently 

 G. limnaeus S. I. Smith) from ponds on the Island of Montreal. 

 The amphipod itself differed in several particulars from the common 

 European form, Gammarus pulex, yet I found on it the same ecto- 

 parasites, Dendrocometes paradoxus Stein and Callidina parasitica 

 Giglioli (13). 



In a foot-note to his paper Otto states that Professor Rudolph 

 Leuckart who provided him with the material for his study, succeeded 

 in bringing some of the embryos of Amph. subtriquetrum to a further 

 stage of development in the Pond Snail, Planorbis marginatus. 



Cuticle. 



The body of Amph. subtriquetrum is covered with a smooth, 

 thick cuticle, which is turned in a little way at the genital opening and 

 the excretory pore, and lines the gut as far as the oesophagus. Where 

 it turns in at the body openings, and over the posterior sucker muscle 

 the cuticle is thin; but over the rest of the body it consists of two 

 well defined thick layers. The outer of these stains deeply and 

 appears quite homogeneous; the inner which is more transparent 

 presents a fine radially striated appearance (Figs. 6, 9 & 10). Otto 

 quotes Looss (14) in support of the opinion that these radial markings 

 are merely a result of preservation and have no connection with the 

 muscular system. On the other hand Walter (15) shows them to 

 be the terminal fibrils of the parenchyma muscles. I was able to 

 confirm his observation that the muscles which cross the parenchyma 

 break up, at the level of the circular muscles, into numerous fine 

 threads that appear to be attached to the outer cuticular layer. Poirier 



