PARASITIC WORMS LEIPEK AND ATKINSON. 



practical acquaintance with tlicsc methods before starting mi the Expedition, ami 

 for the facilities afforded in the Helminthologieal 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 ( 'estodes arc largely the work of Surgeon Atkinson. 



NEMATODA. 



FRKK- LIVING NK M A T< ) I >ES. 



L,eptosomaiwn, Bastian, 1865. 

 1. T-jfptosomatum xi'/nxi/ut. \-. Linstow, ixiiii. (Plate I, tigs. .">, r>. '.).) 



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

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

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

 (Slat. 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 

 on 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 subciiticular shield of chitiuous substance which gives these forms an 

 exceedingly characteristic appearance (PI. 1, fig. 3, <i). This is shown in optical 

 section in PI. I. fig. !>, n. 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 0'12 mm. (Fig. 9, />). 



In a male. 15 mm. long, the nerve-ring (PI. I, fig. 3, <1) crosses the oesophagus 

 at O'(i5 mm. behind the head. The oesophagus measures 2' 3 mm. (Fig. 3, l>}. 

 The lesticiilar tube is a thick solid tube ending anteriorly at 4 Minim, from the 

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

 the auogenital aperture, which lies 5 mm. in front of the blunt and rounded 

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

 outline (11. 1. tig. I), x/i). There is a well-developed shoe-shaped accessory piece (<'/<). 



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

 side and. usually, five on the other (I'l. I. tig. <i. />). ( Mi either side of the middle 

 line is a row of acicular spines. hi the male there is also a series of diagonal 

 muscular bands which briii^ about the ventral coiling of the posterior end of the 

 body, extending forward for I mm. from the auogenital aperture. In the midventral 

 line there is a curious little chitinous rin<>' surrounding a sunken disc (Fi'>-. 6, .v), 



\ O / ' 



recalling the relatively large Slicker seen in III ti m/'/.v. 



