Trematodes and Cestodes 7 G-H 



usually in the middle third of the length ; body narrowing posteriorly more gra- 

 dually than anteriorly ; anterior end bluntly rounded, posterior more pointed ; 

 thickness two-thirds to three-quarters of width. Skin provided with spinelets, 

 hooked and 0-04 mm. in length anteriorly, sparse and smaller behind. Suckers 

 well developed and about the same size, ventral usually a little smaller than the 

 oral; diameter of latter, 0-48 to 0-60 mm., of former, 0-40 to 0-53; oral sucker 

 subterminal, acetabulum situated in the anterior part of the second quarter of 

 the body. 



Spacious prepharynx, may be elongated during life to 0-20 mm. Pharynx 

 comparatively large, spherical to somewhat elongated, 0-4 mm. in length by 

 0-3 in width. Oesophagus 0-12 to 0-15 mm. long, with lining of cuticula. 

 Anteriorly directed diverticula of the intestinal coeca extend slightly beyond 

 the anterior border of the pharynx; coeca themselves extend to posterior end 

 of body without branches or pouches. 



Simple, tubular excretory vesicle, dorsal in position, its blind anterior end 

 lies opposite or extends slightly beyond the anterior border of the anterior 

 testis; gives off two main vessels with wide lumina and likewise dorsal in position. 



Genital pore median, situated close to anterior edge of acetabulum. Spa- 

 cious genital sinus, from 0-1 to 0-2 mm. in length. 



Testes elliptical or elongated oval in shape, outline slightly irregularly 

 indented; anterior often a little smaller than posterior; beginning a little ahead 

 of the equator of the worm they occupy the third quarter of its length; anterior, 

 0-52 to 0-72 mm. in length by 0-24 to 0-30 in breadth, posterior, 0-76 to 0-98 

 and 0-26 to 0-32, respectively. Seminal vesicle, 0-25 mm. in diameter when 

 full, pars prostatica and ductus ejaculatorius, each from 0-17 to 0-20 mm. in 

 length, and cirrus, all within a cirrus-sac provided with inner circular and outer 

 longitudinal muscles and lying dorsal to acetabulum, its posterior end extending 

 nearly half way from latter to anterior testis; cuticular lining of cirrus armed 

 with stout hollow spinelets, 40 to 45ju in length and 7ju in thickness at their bases 

 which are 15 to 19/i in diameter, excepting for a short distance near its end. 



Ovary spherical to oval in shape, 0-16 mm. in diameter, situated to right of 

 midline, immediately ahead of anterior testis and ventral. Oviduct arises 

 dorsally from anterior or medial margin of ovary. Spherical receptaculum 

 seminis, 36/i in diameter at the point of union of Laurer's canal with the oviduct 

 (Fig. 3). Vitelline follicles, extending from the level of the pharynx to the 

 posterior end, surround the intestinal coeca dorsally, laterally and ventrally, 

 the lateral halves of the mantle coming together occasionally between the testes, 

 a little more ventrally than dorsally ; almost meeting dorsally ahead of the aceta- 

 bulum, they remain lateral ventrally. Paired anterior and posterior vitelline 

 ducts, latter sometimes uniting behind the testes for a short distance; dorsal 

 right and left vitelline ducts empty into a dorsal vitelline reservoir which may be 

 as much as 125/z in diameter when full. Uterus extends slightly behind the 

 acetabulum; it is lined with cuticula 45/* in thickness, bearing straight spinelets, 

 40ju in length, and is surrounded by powerful circular muscles and a thick 

 mantle of cells. 



Eggs, from 90 to lOO^i in length by 50 to 59/i in diameter; operculum thinner 

 than the remainder of the shell. 



Habitat. Liver of Phoca hispida Schreber, common rough seal; Bernard 

 harbour (Dolphin and Union strait), Northwest Territories, Canada, October 18, 

 1915; C.A.E. Station 42*. 



The specimens studied differed from Odhner's description of 0. arcticus in 

 the following points : The skin was only sparsely provided with straight spinelets 

 anteriorly, but this was considered to be due to the comparatively poor state of 

 fixation and preservation of the worms, the evidence being that most of the 

 spinelets had been rubbed off; the pharynx was spherical rather than slightly 

 elongated; the anterior coeca extended a little beyond the anterior edge of the 

 pharynx; the blind anterior end of the excretory vesicle extended ahead of the 



