Internal Anatomy (Plate 117, fig. 2)
The septa v/vi, vi/vii, vii/viii, viii/ix, ix/x, x/xi, xi/xii are very muscular and greatly thickened and the septa xii/xiii and xiii/xiv are slightly muscular and thickened.
Alimentary Canal. The pharynx occupies segments i–iv. A strongly muscular, thick-walled gizzard lies in v and the oesophagus extends from vi to xviii. There is a pair of dilated calciferous glands in xvi. The intestine commences in xix; it is wide and thin walled and has no typhlosole. The chloragogen tissue has an unusual form. It consists, in each of the segments posterior to xxii, of two slender lobes, attached to the walls of the intestine and extending up on to the dorso-lateral aspect of the intestine on each side, with a small dorsal gap separating the pair of lobes in each segment.
Vascular System. The dorsal blood vessel is unpaired throughout its length. There are four pairs of hearts, a pair in each of segments × to xiii, arising from the dorsal blood vessel.
Reproductive System. There are two pairs of testes, a pair in x and a pair in xi. Each testis is a small, compact, rounded structure attached by a slender stalk to the ventro-lateral aspect of the anterior septum of the segment. A pair of ovaries, similar in form and position to the testes, occurs in xiii. There are two pairs of spermathecae, a pair in viii and a pair in ix. Each spermatheca consists of an ovoidal sac with an anterior, rounded diverticulum not sharply differentiated from the sac. The whole organ is confined to one segment and opens by a
Fig. 1—Octochactus tricystis. Ventral aspect, segments i–xx.
Fig. 2—O. tricystis. Dissection from the dorsal aspect.
Fig. 3—O. tricystis. Right anterior spermatheca; medial aspect.
c.g., cerebral ganglion: ch., chaeta; cl., clitellum; c.m., copulatory muscles; d.b.v., dorsal blood vessel; d.dlv., duct of the spermathecal diverticulum; div., spermathecal diverticulum; f.p., female pore; g., gizzard; h., heart; int., intestine; m., mouth; mn., micronephridial tubule; m.p., male pore; o., ovary; oe., oesophagus; oe.gl., oesophageal gland; o.f., ovarian funnel; p., prostate; pap., prostatic papilla; perl., peristomium; ph., pharynx; p.p., prostatic pore; pr., prostomium; pv., proventriculus; s., septum; sac, sac containing penial chaetae; sal. gl., salivary gland; s.i.v., supra-intestinal vessel; sp., spermathecal sac; sp.d., spermathecal duct; sp.p., spermathecal pore; t., testis; t.f., testicular funnel; t.pub., tuberculum pubertatis; v.d., vas deferens; v.s., vesicula seminalis.
short narrow duct to the exterior. (Plate 117, fig. 3.) Paired prostates are present in xvii and xix. The prostates are elongate, convoluted, tubular organs extending from a short muscular prostatic duct across the lateral and dorso-lateral aspects of the peritoneum almost to the dorsal mid-line. There are no penial chaetae nor copulatory muscles. The vesiculae seminales are paired, compact organs, a pair in each of xi and xii.
Micronephridia occur in every segment except the first. Those of ii form a fairly compact rounded cluster (similar to the mucus gland of O. multiporous) while those of all the segments posterior to ii are arranged in a narrow band on the lateral and dorso-lateral aspects of the peritoneum on each side of each segment.