. Comparative anatomy and physiology. Chap. VII.] PL A TYHELMINTHES. 249 glandular, and these glands, we may suppose, act on the contents of the blood-vessels which are richly distributed to the nephridium. wider portion, the walls of are muscular, may be upon as The terminal and analogous to a which looked ureter. Bearing in mind that we have in the earthworm to do with a form in which meta- meric segmentation is most markedly expressed, and that this metamerism has clearly affected the nephridia, we are prepared to find a very much simpler condition of things among the Platylielniintlies, an
. Comparative anatomy and physiology. Chap. VII.] PL A TYHELMINTHES. 249 glandular, and these glands, we may suppose, act on the contents of the blood-vessels which are richly distributed to the nephridium. wider portion, the walls of are muscular, may be upon as The terminal and analogous to a which looked ureter. Bearing in mind that we have in the earthworm to do with a form in which meta- meric segmentation is most markedly expressed, and that this metamerism has clearly affected the nephridia, we are prepared to find a very much simpler condition of things among the Platylielniintlies, and, at the same time, to find an arrangement which is more dif- fused. InMonoccelis (Fig. 104), for example, there is a plexus of fine canals, which communicate, on the one side, with large principal canals, of which there are two pairs, one external and one internal, and on the other with funnel-shaped pro- cesses, the entrance to which is guarded by a long cilium ; the principal canals are connected with one another by anastomo- sing branches. In the Deii- droccela, as represented by Polycoelis, the fine canals appear to be absent. If we take the liver fluke as a type of the TTrematoda, we again find that the system of excretory vessels is diffused throughout the whole. Fig. 103.—A single Kephri- dium of ;l?iac7iajtt(. a, Internal orifice, funnel- shaped and surrounded by cilia. It opens into one segment, passes through the septum («) into the next segment, and opens to the exterior by e, external oriflce. (After Vejdovsky.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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