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Show 382 MR. F. E. BEDDARD ON THE [Apr. 19, In the present species, as well as in Eudrilus boyeri1, the 10th and llth segments are occupied by a pair of thin-walled vesicles (woodcut, fig. 1), situated close to each other on either side of the nerve-cord and largely concealed by the superjacent vesiculae seminales. These vesicles in both species alike were filled with a chalk-white mass, which rendered them far more visible than they would have been if void of contents. In Eudrilus boyeri I was unable to ascertain the nature of these structures, and accordingly have not referred to them in m y notes on the anatomy of that species. M. Perrier gives no description or figures of any such structures in his species of Eudrilus. 1 was at first inclined to regard these structures as spermathecae, with which they have not a little resemblance; my sections, however, show that they are really the much-dilated extremities of the vasa deferentia just before they open into the funnel. Fig. 11 (Plate XXXIII.) illustrates a transverse section through one of these structures, and shows the continuity between the cavity of the vesicle and the terminal funnel. The funnel of the vas deferens is (fig. 11, c), as usual, a much plicated membrane, composed of ciliated cells with an underlying layer of muscular fibres, among which are numerous blood-capillaries; the terminal vesicle of the vas deferens (fig. 11, b) has exactly the same structure ; it is lined by a single row of cubical ciliated cells ; in the interior of each of these is a distinct nucleus. Outside the layer of ciliated cells is the muscular coat, composed of fibres running in different directions ; tbe thickness of the muscular coat is not much greater than that of the cellular layer. The anterior pair of vasa deferentia funnels, as shown in the figure (fig. 11), project into the interior of tbe vesicula seminalis ; there is, however, a space left between the masses of spermatophores and the ciliated cells ; the whole of the vesicle of the vas deferens, with the exception of the under surface, is completely surrounded by the vesicula seminalis; the delicate fibrous wall of tbe latter appears to be here in actual contact with the muscular wall of the vesicle ; there is, at any rate, no space left between the masses of spermatophores and the wall of the vesicle. The posterior pair of vas-deferens funnels appear at first sight to be completely free from all connection with the vesiculae seminales of their segment. The vasa deferentia, however, do not open freely into the body-cavity, but into a delicate fibrous sac (which encloses the ventral blood-vessel, and is consequently perforated by the lateral "hearts" of this segment, which unite the ventral with the dorsal vessel). This sac is median and unpaired; it is connected with a short diverticulum on either side, which contains the testis ; groups of spermatophores are found in the interior of the sac ; and although I have not succeeded in tracing its continuity with the vesiculag seminales, I have little doubt that the separation is only secondary, if not altogether accidental; it corresponds to the median portion of the vesiculae in segment 10. rl he vasa deferentia remain separate for the whole of their course ; the two vasa deferentia of each side only become united within the tunic'of the prostate gland. They are furnished with an unusually 1 P. Z. S. 1886, p. 302. |