. A manual of elementary zoology . Zoology. THE SWAN MUSSEL 315 are continuous with the labial palps, which are a pair of triangular flaps, one outside the other, on each side of the body, the outer palps being joined in front of the mouth by the upper lip and the inner behind the mouth by the lower lip. The palps are ciliated, and their surfaces which are towards one another are crossed by fine furrows, which lead upwards towards the groove between them. This is continuous with the corners of the mouth, and the whole forms an apparatus by which small organisms and other fine organic particles

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. A manual of elementary zoology . Zoology. THE SWAN MUSSEL 315 are continuous with the labial palps, which are a pair of triangular flaps, one outside the other, on each side of the body, the outer palps being joined in front of the mouth by the upper lip and the inner behind the mouth by the lower lip. The palps are ciliated, and their surfaces which are towards one another are crossed by fine furrows, which lead upwards towards the groove between them. This is continuous with the corners of the mouth, and the whole forms an apparatus by which small organisms and other fine organic particles are gathered from the water. Fig. 224.—A, A horizontal section through a gill of the swan mussel, under low magnification ; B, a single filament of the same, more highly magnified. bl.sj>., Blood spaces ; y?/., filaments ; /., side of filament towards interlamellar space ; i.f.j., interfilamentar junction; ?'././., interlamellar junction; i.l.sp., inter- lamellar space; o., outer side of filament; sk.r., sections of the chitinous skeletal rods which support each filament. in the mantle cavity and swallowed. Each of the gills consists of two lamella continuous along their ventral edges. As there are two gills on each side of the body, there are on each side four lamellae. Each lamella is composed of very numerous vertical filaments whose inner sides (that is, the side of each towards the other lamella) are fused together at irregular intervals, so as to form a ribbed plate pierced by numerous openings between the ribs leading into the interlamellar space of the gill. The filaments of the two lamellae of a gill are continuous, each 21. 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 work.. Borradaile, L. A. (Lancelot Alexander), 1872-1945. London : H. Frowde, Hodder & Stoughton

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