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Internal Anatomy (Plate 14. fig. 2)
The first septum occurs at the intersegment iv/v. The septa vii/viii, viii/ix, ix/x, x/xi and xi/xii are muscular and thickened.
Alimentary Canal. A rounded muscular pharynx occupies the first four segments. The pharynx is covered dorsally and laterally by a downlike mass of salivary glands. There is a thin-walled proventriculus in v and a stout muscular gizzard in vi. The oesophagus extends from vii to xvi and there are no oesophageal glands. The intestine commences in xvii, is thin-walled and has a small typhlosole.
Vascular System. The dorsal blood vessel is unpaired throughout its length. There are four pairs of dilated hearts in x, xi, xii and xiii, rising from a supraintestinal vessel which extends only through those four segments.
Reproductive System. There are two pairs of testes in x and xi. The testes have a lobate form and their funnels are on the posterior septa of the segments. The two slender vasa deferentia of each side are prominent, lying side by side on the ventro-lateral aspect of the peritoneum They remain distinct from each other for most of their length, fusing just before they enter the prostatic duct, in xviii. There is a single pair of ovaries in xiii. Each ovary appears as a thin lace-like lamina attached to the anterior septum of the segment. The ovarian funnels are very prominent white structures on the posterior septum of xiii, and the short oviducts, which open to the exterior in xiv, are very much thicker than the vasa deferentia. A single pair of spermathecae occurs in viii. Each is a large, roughly ovoidal, thin-walled sac with a small, thick-walled digitate diverticulum opening into the anterior aspect of its duct. (Plate 14, fig. 3). The whole organ is confined to the eighth segment. The prostates are large, coiled, tubular organs, extending through the segments xviii, xix, and xx and opening to the exterior in xviii by wide muscular ducts. The prostatic duct of each side fuses with the corresponding vas deferens close to the body-wall in xviii. There are two pairs of large, finely racemose vesiculae seminales surrounding the lateral aspects of the oesophagus in xi and xii.
Micronephridia commence in ii. There is a compact cluster of micronephridial tubules on the ventro-lateral aspect of the peritoneum on each side of the segments. The individual tubules are very long and are twisted like corkscrews.
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Remarks. This species most closely resembles M. (Tokea) sapida Benham (1904), collected from Ruatahuna, between Rotorua and Lake Waikaremoana. It agrees with Benham's species in size, colour, and in many points of its anatomy, but the number and form of the spermathecae in the two species are markedly different. M. sapida has three pairs of spermathecae, each with a small globular diverticulum, while M. fuscus has only one pair of spermathecae and their diverticula are digitate. The number and form of the spermathecae and their diverticula are very reliable systematic characters and serve to distinguish the two species one from the other.
Megascolides irregularis n.sp. (Plate 15, figs. 1–3)
One specimen of this large worm was collected near Tangowahine, North Auckland. Other specimens have been collected from localities in the same area. The specimen on which the description is based is 117 mm. in length with 120 segments, and has an almost uniform diameter of 7·5 to 8 mm. It is purplish-red in colour dorsally, and pale ventrally. The clitellum is buff in colour and completely surrounds xiv to xvii, except for a small area on the ventral surface of xiv where the female pores occur.
The prostomium is epilobous. There are eight chaetae on each segment, but their arrangement is most irregular. They are not arranged in pairs, but occur four on each side of each segment, scattered indiscriminately. The distance between corresponding chaetae a on each segment is more or less uniform anterior to the prostatic pores, but varies considerably posteriorly.
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There are two pairs of spermathecal pores, a pair at 7/8 and a pair at 8/9. On each side the pores lie in line with chaeta a. A single pair of female pores is present on xiv, very close together in a small pale area covering the ventral mid-line. On xviii is a pair of prostatic pores surrounded by tumid lips. Each pore is in line with the chaetae a on the same side. Across the ventral mid-line, at the anterior margin and at the posterior margin of this segment is a small tuberculum pubertatis.
Nephridiopores are not visible externally.