PARASITIC WORMS— LET PER AND ATKINSON. 23 



practical acquaintance with these methods before starting on the Expedition, and 

 for the facilities afforded in the Helminthologica] Department for working out the 

 material upon his return. 



The elucidation of the anatomical structure of the various forms and the 

 descriptive account of the Cestodes are largely the work" of Surgeon Atkinson. 



NEMATODA. 



FKEE - 1, 1 VINO NEMATODES. 



Tj'ptoMomatum, Bastian, L 8 6 5. 

 L. Leptosomatum setomm, v. Linstow, L 8 96. (Plate I, figs. 3, C>, 9.) 



A tube containing a large number of this species occurred in the collection made 

 by Mr. Lillie from a depth of 250 fathoms in McMurdo Sound. Specimens were 

 also collected from a depth of 150 fathoms off Inaccessible Island, Lat. 77" 38' S. 

 (Stat. 320). 



The vitreous appearance of the cuticle distinguishes this species from parasitic 

 forms. The cuticle is not striated, but carries fine acicular spines in longitudinal rows 

 mi the anterior part of the body, and, in the male, on the ventral aspect in the region 

 of the genital papillae and the anogenital opening. Both extremities of the worms 

 are bluntly rounded. The head-end is somewhat the more abruptly truncated. The 

 head has a subcuticular shield of chitinous substance which gives these forms an 

 exceedingly characteristic appearance (PI. I, fig. 3, it). This is shown in optica] 

 section in PI. I, fig. !). a. The arrangement of the spines on the head has not been 

 fully elucidated. They extend in linear series from the tip of the head backwards 

 for a distance of about (')• I 2 mm. (Fig. 9, b). 



In a male, 15 mm. long, the nerve-ring (PI. I, fig. 3, </) crosses the oesophagus 

 at O'tio mm. behind the head. The oesophagus measures 2 - 3 mm. (Fig. 3, b). 

 The testicular lube is a thick solid tube ending anteriorly at 4" 6 mm. from the 

 head in a blunt digitate process. It passes directly backwards without coiling to 

 the anogenital aperture, which lies 0-5 mm. in front of the blunt and rounded 

 tail. The spicule is a bent, short chitinous structure not unlike a boot-last in 

 outline (PI. 1, fig. 6, sp). There is a well-developed shoe-shaped accessory piece (up). 



The genital papillae are sessile and are all preanal. There are four on one 

 side and. usually, five on the other (PI. I, tig. (!, />). On either side of the middle 

 line is a row of acicular spines. In the male there is also a series of diagona] 

 muscular bands which bring about the ventral coiling of the posterior end of the 

 body, extending forward for I nun. from the anogenital aperture. In the midventral 

 line there is a, curious little chitinous ring surrounding a. sunken disc (Fig. 6, *), 

 recalling the relatively large sucker seen in TIeterakis. 



