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Show 1886.] MR. F. E. BEDDARD ON A LARGE EARTHWORM. 171 (d), which is a single tube, and not composed of two separate or incompletely fused halves as in A. multiporus1 and other Earthworm*, communicates with the ventral vessel by seven transverse hearts (h) situated in segments 8-14 inclusive-a pair to each segment. The first three pairs are of less calibre than the following four, and appear to arise simply from the dorsal vessel; the four posterior pairs of hearts communicate also with a small supra-intestinal vessel, which, as shown in the figure (sn), lies beneath the dorsal vessel but above the intestine ; in the anterior part of the body a pair of lateral vessels (I) supply the body-wall; in the 11th or 12th segment these vessels pass beneath the intestine and unite to form a single subintestinal vessel. This vessel appears to be continuous posteriorly with a vascular space within the walls of the alimentary canal. Each of the two anterior pairs of hearts supplies the spermatheca of its own segment; a strong branch arises from the vessel just before it unites with the ventral vessel, and a corresponding branch from the latter is also distributed to the spermatheca. Body-cavity.-The body-cavity, as in all other Earthworms, is divided into segments by mesenteries which extend from side to side of the body ; in the six anterior segments the mesenteries are more or less distinct, but there are in addition a number of muscular bands and tendinous-looking threads which bend the pharynx down to the body-wall, often passing through the mesenteries on their way; the gizzard and a portion of the anterior region of the oesophagus are only attached to the body-wall by a very few slight threads, mesenteries being absent in this region of the body. The mesentery which bounds tbe tenth segment behind and the succeeding four mesentries are specially thickened and muscular. Nephridia.-There is a very considerable variation in the characters of the nephridia in this genus, and I have already2 referred to what has been written on the subject. In the present species the nephridia (fig. 6, n) are very conspicuous, especially in the anterior region of the body as far back as the 19th segment or thereabouts; in tbe posterior segments they are present but appear to differ slightly, principally in size, from the anteriorly placed nephridia. The external apertures are plainly visible in front of the dorsal pair of setae in all the seta-bearing segments of the body ; that is to say, the first segment of the body appears to be without nephridia and only this segment. The glandular portion of the nephridium forms a closely packed tuft of tubules which has much the appearance of the nephridia in those species of Perichceta3 in which these organs have been described ; this glandular tuft lies in the region of the ventral pair of setas and close to the mesentery which forms the anterior wall of its segment ; the nephridium communicates with the exterior by a long, widish, thin-walled duct. 1 See F. E. Beddard "On the paired Dorsal Vessel of certain Earthworms." Proc. Eoy. Phys. Soc. 1884-5, p. 424. 2 P. Z. S.. 1885. p. 822. 3 E. g. Perichceta indica, Horst, Niederl. Arch. f. Zool. Bd. iv. (1879), pi. viii. fig. 3, x. 1 b 12* |
