AUT. 13 TKEMATODE PAEASITES OF MAKINE MAMMALS PRICE 15 



KEY TO SPECIES OF ORTHOSPLANCHNUS 



1. Body almost cylindrical ; ventrally the vitelline follicles encroach 

 on the testicular and uterine fields but do not extend ante- 

 riorly as far as pharynx fraterculus (p. 16). 



Body somewhat flattened ; ventrally the vitelline follicles do 

 not encroach on testicular and uterine fields but extend 

 anteriorly beyond level of posterior end of pharynx arcticus (p. 15). 



ORTHOSPLANCHNUS ARCTICUS Odhncr, 1905 



Plate 4, Figxjkes 17, 18 



Desc7^ption. — Orthosplanchnus : Body slightly flattened, 3.5 mm 

 to 7 mm, usually 4.5 mm to 6 mm long by 850/a to 1.15 mm wide, 

 tapering toward both ends, the posterior part of body being slightly 

 more attenuated than the anterior part. Cuticle spiny throughout, 

 the spines on the anterior part of body being about 40/x long, while 

 those at both ends are somewhat smaller. Oral sucker 480/a to 600/i 

 in diameter, subterminal in position; acetabulum 450;U, to 530/a in 

 diameter, situated about one-fourth of body length from anterior 

 end. Prepharynx about 200/t long, pharynx about 400|U, long by SOO^a 

 wide, esophagus 120ju to IbOjx long. Intestine with short anteriorly 

 directed ceca, one on each side, which extend to level of anterior end 

 of pharynx, and long posterior ceca, which extend to end of body; 

 both the anterior and posterior ceca are simple and without diver- 

 ticula. Excretory pore terminal ; excretory vesicle simple and tubu- 

 lar, and extending anteriorly to level of anterior margin of anterior 

 testis. Genital aperture preacetabular, median ; genital sinus spa- 

 cious. Cirrus pouch pestle shaped and extending caudally to about 

 midway between acetabulum and anterior testis (about two-fifths 

 of the distance from acetabulum to ovary, according to Cooper, 

 1921) ; seminal vesicle more or less spherical and about 250/^ in 

 diameter when filled with sperms, more tubelike when empty ; pars 

 prostatica cylindrical, 170/^ to 200/x long, and set off from the seminal 

 vesicle by a sharp constriction; ejaculatory duct about the same 

 length as pars prostatica; cirrus protrusible and spiny, the spine? 

 40/A to 45/x long by 7ju, wide at their bases and inseited into a basai 

 disk ISju, to 19/t in diameter by 12/a thick. Testes elongated oval in 

 shape, with indented margins; the anterior testis is usually slightly 

 smaller than the posterior; they are tandem in position and situ- 

 ated in the anterior half of the posterior part of the body. Ovary 

 entire, transversely oval in shape, situated cephalad of anterior 

 testis and to the right of the median line; seminal receptacle very 

 small; Laurer's canal present. Vitellaria profusely developed and 

 extending both dorsal ly and ventrally of intestinal ceca from the 

 level of the pharynx to the posterior end of the body ; anterior to 



