. Elements of Comparative Anatomy. EXCEETOEY OEGANS OF BEACHIOPODA. 313 even tliougli their fiinction. be modified. There are either one or two pairs of them. When there are four, two of them belong to the so-called dorsal, and two to the ventral half (Rhynchonella) ; this points to the presence of two metameres, which have disappeared in this portion of the body. The dorsal ones are absent in Lingula and the Terebratulida. The canals, which generally open to the exterior near the base of the arms, open into the coelom, after having taken a bent course, by funnel-like enlargements (Fig. 166, r
. Elements of Comparative Anatomy. EXCEETOEY OEGANS OF BEACHIOPODA. 313 even tliougli their fiinction. be modified. There are either one or two pairs of them. When there are four, two of them belong to the so-called dorsal, and two to the ventral half (Rhynchonella) ; this points to the presence of two metameres, which have disappeared in this portion of the body. The dorsal ones are absent in Lingula and the Terebratulida. The canals, which generally open to the exterior near the base of the arms, open into the coelom, after having taken a bent course, by funnel-like enlargements (Fig. 166, r), which are distinguished by their radially-arranged folds. This orifice passes througli the ileoparietal band, and is thus directed. Fig. 166. Lateral view of the organisation of Waldheimia anstralis. D Dorsal, V Ventral surface. P Stalk. II Spirally-coiled arms, hr Brancliial filaments, c An- terior -wall of the perivisceral cavity, d Oesophagus, d' Mid-gut. h Liver, h.' Its openings into the mid-gnt. r Internal orifice of the right oviduct (some folds only of the left oviduct can be seen), e Brachial canal, vi m' m" in* Muscles to move the valves of the shell (after A. Hancock). towards the pericardial cavity. The ileoparietal band resembles therefore, in its relation to the internal orifice, a dissepiment of the Vermes (of. supra, § 243). Although the walls of these canals appear to be glandular in character, owing to the possession of projections, villous processes, or folds, we know nothing of their function, save that they have a relation to the generative organs; so that they appear to form an oviduct, and have indeed been hitherto regarded as being such. And as the looped-cauals serve as parts of the generative apparatus in the Gephyrea and Annelides, it is not to be wondered at that they have the same relations in the Brachiopoda; but this does not exclude the possibility of their having an excretory function Please note that these images are extracted f
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