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Show I 887-] ANATOMY OF EARTHWORMS. 391 body by being longer and thinner. In Urochata one or more pairs ol the clitellar setae are larger and beset with a number of tiansverse notches. I have recently described an identical modification in the clitellar setae of the closely allied genus Thamnodrilus l. Horst distinguishes 2 the clitellar setae of Khinodrilus by their greater size. In Lumbricus the modification of the setae is not confined to the clitellum, but is also found in the neighbourhood of the generative orifices. I believe that in the genus Perichata no modification of the setae at all comparable has ever been described except by myself in P. armata and P. ceylonica. The first-named species is remarkable for the fact that the terminal part of the ejaculatory duct opens on to the exterior in common with a thin-walled muscular sac, the interior of which is filled with a number of peculiar setae, the shape of which can be best appreciated by an inspection of the figure which accompanies m y memoir. Perichata ceylonica is the only other species of the genus in which this arrangement is repeated, and the arrangement is practically identical with that which obtains in P. armata. It is perfectly clear that these sacs of penial setae correspond in every way to the penial setae occasionally developed in other Earthworms for example in the genera, Acanthodrilus and Typhceus. In Acanthodrilus it is certain that penial setae are not supernumerary structures developed only at the period of sexual maturity, but they replace the ordinary setae of the pair which correspond to the male generative aperture. EXPLANATION OF PLATE XXXIII. Fig. 1. Transverse section of vas deferens; highly magnified. 2. Testis {t) and vesicula seminalis {v.s). 3. Transverse section of oesophagus and ventral gland of llth segment. d, dorsal blood-vessel; si, supra-intestinal (double); h, heart; h', branch supjDlying walls of oesophagus and gland; p, peritoneal coat. 4. Section through gland (rudimentary ovary?) attached to wall of 13th segment, b, gland; a, muscular tube enclosing it; to the left the tube is seen to form a bend and to be cut across twice. 5. Ventral aspect of oesophagus in segments 10 and 11, to show suboesophageal glands (a). Bifurcation of subintestinal vessel illustrated in this figure. 6. Lateral view of same region. Bifurcation of supraintestinal vessel, as well as subintestinal vessel, illustrated. 7. Transverse section of oesophagus in 10th segment; left-hand figure through opening of suboesophageal gland (highly magnified in fig. 3), right-hand figure in front of or behind opening of gland. Compare with figs. 5 and 6. 8, 9, 10. Transverse sections through prostate gland at various levels. 11. Opening of vas deferens funnel into vesicula seminalis. a, vesicula crammed with developing spermatozoa ; c, ciliated funnel; b, vesicle of vas deferens. 12 Section of oviduct, to show ciliated epithelium and muscular walls. 13. A portion of fig. 8 more highly magnified. I, lining epithelium ; e\ glandular cells; m, transverse longitudinal muscles. 14. Section of epidermis, a, problematical body ; b, glandular cells. 1 P Z. S. 1887, pt. i. 2 Notes from Leyden Museum, 1886. |
