§2 ALICE L. EJJBLETOX ON THE STRUCTURE AND 



while tlie longiiudinal fibres are almost wanting; the epithelium is correspondingly 

 leduced anl is devoid of glands (PI. 8. fig. 16). This narrow, muscular, non-glandular 

 part is probably to be looked upon as a gizzard, following as it does immediately upon 

 the crop-like region. Jameson describes the " crop " in Thalassema neptuni as coming 

 behind the gizzard ; though it is difiicult to see what its use could be in such a position, 

 for the crop is essentially a glandular distensible part in which food collects before it 

 can enter the narrow muscular gizzard, where it is crushed previous to its passage into 

 the delicate intestine. I find the cilia in somB specimens extend back as far as the 

 beginning of the intestine, though this is apparently an individual variation. 



At the posterior end of the body this narrow gizzard, which extends for nearly 5 cm., 

 widens out into the thin-wall^d intestine, and at the same time it turns forwaixls, 

 becoming a veritable tangle of complicated coils and loops ; mesenteric strands reappear 

 at this point which attach the coils, irregularly, to the body-wall. The beginning of the 

 intestine proper is marked by the appearance of the ciliated groove on the ventral side, 

 Avhich 25 cm. further on gives place to the collateral intestine (or siphon), at a point 

 about 12-5 cm. from the mouth. The intestine continues as far as the rectum (or large 

 intestine) ; its walls are very delicate, possessing very few fibrous elements ; its epi- 

 thelium is glandular and is raised into long slender villi (PI. 8. figs. 17, 17 a) ; above 

 the ciliated groove and collateral intestine runs a band of longitudinal muscle (PI. 8. 

 figs. 17, 21</, 21 b, m.L), which is continued on the rectum (Pi. 8. fig. 18, m.l). In all 

 the specimens 1 examined, the origin and end of the collateral intestine are clear and 

 unmistakable, though Drasche says he was unable to find the openings. At its origin 

 (fig. 19), the transition from the ciliated groove to the accessory intestine is very abrupt, 

 the latter standing up from the alimentary canal with a somewhat dilated and swollen 

 end. Posteriorly it passes over gradually into the ciliated groove, ending without a 

 dilatation, about 10 cm. from the anus (fig. 20). On opening tlie alimentary canal at 

 these points, and pinning back the walls so as to expose the interior, the aperture leading 

 from the collateral intestine into the alimentary canal is jilainly visible under a 

 dissecting microscope (PL 8. fig. 21, o). Beneath the collateral intestine there is a 

 shallow groove Avhich Jameson has called the "secondary ciliated groove" (fig. 21). 

 The collateral intestine has received various names : it is sometimes referred to as the 

 siphon, or accessory intestine; Spengel calls it the '• Nebeudarm," while Greeff mistook 

 it for a blood-vessel and speaks of it as the "Darmvene." 



The rectum (PI 7. fig. 5; PI. 10. fig. 39, r.) is a straight, wide, thick-walled tube, 

 proceeding from the anus along the left side of the nerve-cord as far as the segmental 

 organs; it is held in place by a row of mesenteric filaments inserted exactly opposite the 

 lone-itudinal muscle, i. e. inserted on the dorsal side. At its anterior limit, where it 

 passes into the intestine, there is a marked constriction, though no sphincter muscle can 

 be seen on microscopic investigation. Tiiere are two endoparasites in this rectal tract — 

 a probably new species of the Infusorian Trichodma, and a Copepod, which is evidently 

 an entirely unknown form *. 



* Tlds was confiriued by Dr. G. S. Brady, F.R.S., to \\liom some specimens were submitted. 



