Beedham g e (5 Ergebnisse)
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Anbieter: Acanthophyllum Books, Holywell, FLINT, Vereinigtes KönigreichAcanthophyllum Books
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Paper covers. Zustand: Fine. No Jacket. 1st edition. Scarcely used. 236 pp. Weight: 1 Language: English.
- Softcover
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Zustand: Very Good. 239, line drawings. . PB. Spine faded. Vg. (Hulton Group Keys). Keys and descriptions of commoner British Molluscs (282 species illustrated) with identification keys. [9780717505937].
Verlag: 1st. Ed. Pub. Hulton Educational. 1972, 1972
Anbieter: C. Arden (Bookseller) ABA, Hay-on-Wye, Vereinigtes KönigreichC. Arden (Bookseller) ABA
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In den Warenkorbpp.239 with b/w. illus. throughout. 8vo. Nr. fine softback.
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In den WarenkorbThe cuticle of Proneomenia consists of a mucoid matrix containing calcareous spicules and is secreted by the mantle epithelium at the base of the ventral (pedal) groove and over the general body surface. Histochemical examination shows the matrix to be composed of a glycoprotein complex with high acid mucopolysaccharide and low…protein contents in which tanning plays little part in stabilization. The cuticle of the Aplacophora is tentatively equated with an early mucoid stage in the evolution of the molluscan shell and it is suggested that secretion of additional protein, followed by hardening by quinone-tanning, are necessary further stages before a calcified shell evolves. The aplacophoran cuticle is compared with that of Acanthochitona (Polyplacophora) and, although they are similar in many respects, the latter has in addition a discrete inner cuticular layer whichmay act as a semi-conducting membrane in the deposition of the calcareous plates. The spicules are similar in both groups, each being secreted within a thin cup-like membrane which exhibits somewhat similar properties to the inner cuticle. 9 pp., 2 figs, gr. 8.
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In den WarenkorbThe structure and growth of the polyplacophoran shell, characteristically consisting of eight plates surrounded by a girdle, is examined in the light of current views on the relationships of mantle and shell in the Bivalvia. The periostracum and outer and inner calcareous layers of the shell of the latter group are homologous wi…th the cuticle, tegmentum and articulamentum respectively of the shell of the Polyplacophora. The margin of the mantle consists of a large marginal fold, which secretes the cuticular girdle, and a small accessory fold bearing mucous cells. These are functionally comparable with all three folds of the mantle margin found in other molluscs, although anatomically the marginal fold of the chitons probably represents only the inner surface of the outer fold of the mantle margin. The cuticle not only forms the girdle, which bears calcified spines or spicules, but also extends between the shell plates. The principal part of the cuticle consists largely of mucopolysaccharide material but there is also a thin discrete inner region which is similar chemically to the periostracum of other molluscs. The cuticle, possibly without spines, probably covered the entire dorsal surface of a primitive placophoran and beneath this, plates developed. As these grew the cuticle became worn away except marginally and between the plates. It is suggested that a covering of mucus over the visceropallium may have been the forerunner of the molluscan shell and the possibleevolutionary relationships of the shell throughout the Mollusca are discussed. 17 pp., 6 figs, gr. 8.
