THE NEPHRIDIUM OF LUMBEICUS. 331 



Fig. 8. — A portion of the apex of the second loop, from a living nephri- 

 dium (Zeiss, 4, B), in order to show the second ciliated tract, c io c/ (see also 

 Fig. 1), iu the outer narrow tube ; together with the adjacent non-ciliated 

 portions, ves. Vesicular connective-tissue cells. 



Fig. 8ff. — A portion of another nephridium, to show the irregular character 

 of the lumen (? remnants of branchings) of the narrow tube. 



Fig. 9. — A portion of Fig. 8 under a higher power (Zeiss, 4, E), showing 

 the character of the wall. 



Fig. 10. — A portion of Fig. 9 — a living nephridium — still further enlarged, 

 to show the termination (c) of the ciliated tract at the apex of tlie second 

 loop. This tube at c is seen in optical cross-section owing to its sudden bend. 



Fig. 11. — A small portion of the "middle tube" in optical section, 

 during life (Zeiss, 4, E). It shows the character of the protoplasm, the limits 

 of the cells, the excretory products in the protoplasm and in the lumen, and 

 the double row of cilia. The arrow points towards the ampulla (see Fig. 1). 



Fig. 12. — The surface of a portion of the ampulla (drawn from a living 

 nephridium under Zeiss, B). It shows the shape and boundaries of the 

 constituent perforated cells. 



Fig. 13. — An optical section of a small portion of the ampulla (drawn from 

 a living nephridium with Zeiss, E). The differentiation of the protoplasm of 

 the cells into " central " and " peripheral " regions and the radial arrange- 

 ment of the granules are shown. The circles in the lumen represent the 

 spherical excretory products. 



Fig. 14. — An optical section of the " wide tube," drawn from a living 

 nephridium (under Zeiss, E). 



Fig. 15. — A transverse section across the third loop, near its apex, at 

 about the level of j in Fig. 1 (from a series stained in borax carmine ; drawn 

 with Zeiss, 4, E). It is fully explained in the Plate. The middle tube shows 

 the characteristic spherular character of the protoplasm of its wall, and the 

 two rows of cilia ; the granules in the lumen are the remains of excretory 

 products, b. v. Blood-vessels, n. Nuclei of their endothelium, c. t. Vesi- 

 cular connective-tissue cells, the limits of the cells not being visible in 

 the sections, nc. Their nuclei, c. ep. Nuclei of coelomic epithelium, x. A 

 curious fibrous appearance sometimes visible in sections. 



Fig. 16. — A transverse section through the muscular duct (from the same 

 series as Fig. 15, under Zeiss, 3, F). ep. The lining of the duct. mus. c. 

 Muscle-cell. n. mus. Nucleus of muscle-cell. c. ep. represents coelomic 

 epithelium. 



Fig. 17. — A portion of a transverse section through the body-wall of 

 Criodrilus lacuum, in the clitellar region, iu order to show the absence of 

 a muscular duct in this genus, and the consequent perforation of the longi- 

 tudinal muscles by the " wide tube." y is a group of connective-tissue cells, 



