PARASITIC WORMS -LEIPER AND ATKINSON. 



37 



the other Trematodes from this fish. None were sexually mature. The largest 

 specimen measures only 074 mm. in length. The greatest breadth is G"4 mm., in 

 the region of the ventral sucker (Fig. 21, />), whence the worm becomes bluntly pointed 

 both anteriorly and posteriorly. The skin is smooth. The ventral sucker occupies 

 almost the entire width of the worm, measuring 0"36 mm. transversely by 0*20 mm. 

 antero-posteriorly. Its muscular wall, as seen in optical section, is ()• I mm. thick'. 

 The oral sucker (a) is about one-quarter the size of the ventral sucker. A muscular 

 pharynx succeeds the oral sucker, and the alimentary canal then immediately divides 

 into two dilated main gut-branches, which terminate blindly a short way behind the 

 ventral sucker (//). The testes lie one in front of the other, somewhat diagonally, and 

 the ovary is found on one side of the testes. These three bodies are smooth and 

 round, measuring about O'l mm. in diameter. The extent of the yolk-glands cannot 

 be determined. No eggs were present in any of the specimens. Details of the cirrus 

 and other structures could nol lie made out from the material available. The excretory 

 vesicle (ex) is cylindrical and in some specimens is rendered conspicuous by the presence 

 of fine black pigment-granules. 



MONOSTOMOIDEA. 

 ( )t/ui<></<tsfci\ -lagerskiold, 1891. 

 18. Ogmogaster j>/ irut us (Creplin). (PI. Ill, fig. 16. Text-figs. 5 and 6.) 

 Monostomum pKcatum, Creplin, 1829. 



Hosts. The specimens of this Monostome were obtained from both Weddell's 

 Seal (Leptunychotes iceddelli) and the Crab-eating Seal (Lobodon carcinophagus). 

 Some occurred looseh' attached to the coats of the small intestine, others upon the 

 contents of the intestine. 



Parasite. — In colour the worms were nearly always a light pink, like that of some 

 corals and shells. The colour always disappeared on fixation, when they became 

 isabelline to brown. The parasite is in shape exactly like the half of a hemp-seed split 

 longitudinally. 



The size of the specimens varies considerably — those obtained from the Crab- 

 eating Seal being generally the largest. The average length is 5-6 mm., none being 

 above 8 nun. ; they are, therefore, slightly smaller on the whole than those from 

 Balaenojrtera acutorostrata and B. musculus* described by Jagerskiold. The greatest 

 transverse diameter varies from 4" 5 mm. to 5 • 5 mm. The ventral aspect is hollowed 

 and cupped, the dorsal convex from end to end and from side to side. The worm is 

 narrower at the cephalic end than at the caudal end ; its greatest diameter being at 

 the equatorial line. The ventral surface is raised into a succession of longitudinal rugae 

 (PI. 111. tig. 16, / ), averaging in number fourteen to fifteen, as ascertained from eross- 



The Common Rorqual. — S.F.H. 



H 2 



