OCR Text |
Show 1880.] THE GENUS GIRASIA. 295 Animal.-The left dorsal lobe (l.d.l. Plate XXIV. figs. 3, 4, 5) is large in front, and extends from the respiratory orifice to the left margin. The right dorsal lobe (r.d.l.) extends from the same part to the posterior right margin. The shell-lobes are connected all round the periphery of the mantle-zone, but are reduced in size, and present two distinct right and left contractile lobes ; the right extends to and covers the apex of the shell, while the left extends over the edge of the body-whorl for a distance of 0*3 to 0*5 inch, leaving the posterior and the greater portion of the upper surface of the shell uncovered (we have here a true approach to what is seen in the subgenus Macrochlamys). The posterior margin of the shell is not sunk in a depression of the hinder part of the foot, but the upper surface of the foot extends in an unbroken ridge to the mantle-zone. Extremity of the foot truncate, with a large linear mucous gland, the pedal line very distinct, as well as the lateral markings on the surface of the body. Genital aperture at the lower and outer base of the right tentacle. Animal reaches quite 4 inches in length. Description of Genital Organs of A. gigas. Small var., Khasi Hills (Plate X X V . fig. 1).-The ovo-testis was not seen ; the hermaphrodite duct (h.d.) is much convoluted at the anterior end, where it divides ; the shape of the albumen-gland was also unobserved, and had apparently not been preserved in the spirit. The oviduct (ov.) was very closely convolute, and arranged in four sharp folds upon the posterior portion of the spermatheca (sp.), to which it is apparently held by muscular tissue. The prostate is wide, regular, and ribbon-like, much and closely convolute, giving off the vas deferens not far above the junction of the spermatheca with the oviduct; this is very long, extending forward between the inverted eye-tentacles, forming a loop among the muscles of the buccal mass. The penis is bent on itself at the point where the retractor muscle is given off (Pc. fig. 4 ) ; and a short, blunt, rounded portion extends beyond the insertion of the vas deferens (pd.), corresponding to the flagellum in some species, or the Kalksack of Semper (the caecum calciferum vasis deferentis). The retractor muscle of the penis has its attachment, together with the e} e-tentacles, in the usual position, close below the apex of the shell, near the posterior margin of the body-cavity (Plate XXIV. fig. 3 m). Detailed Anatomy of Penis of G. gigas (Plate X X V I . figs. 2, 3). On the removal of the outer muscular sheath, the anterior end is of a hollow cone-shape (a), which, on being cut away, presented within a cup-shaped depression (a!), and exposed the duct of the penis. It contracts suddenly, and continues as a smooth stout tube of equal size for about 0*25 inch, where it expands again (b) into a stouter portion of cylindrical form, which is 0*55 inch long, and continues, with gradually lessening thickness, up to the part where it is turned suddenly backwards, and close to where the retractor muscle is given off (c). On removing the outer layer a chitinous sheath was exposed lying |