. Die cyclopaedia von Anatomie und Physiologie. Anatomie, Physiologie, Zoologie. 562 SHELL. Durch das Zusammenwachsen von einer Reihe von Zellen in linearer Richtung angeordnet. Sie sind in der Regel Abb. 415.. Tubular shell-Struktur in einem externen Oberfläche von anomia Ephippium. 250 Durchmesser vergrößert. Am häufigsten in Tanks, deren äußere hat eine Blättrig oder skulpturalen Charakter; und nicht un-häufig deutlich gesehen werden, können Sie direkt auf die protuberanzen der sur-Face, - wie in Lima scabra und verschiedene Arten von Chama. Sie sind auf keinen Fall beschränkt sich jedoch auf die Tanks so charakterisiert; noch sind.

• Bildanbieter: Central Historic Books / Alamy Stock Foto
• Bild-ID: PFN55C
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• Format: 1615 x 1547 px | 27,3 x 26,2 cm | 10,8 x 10,3 inches | 150dpi

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. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 562 SHELL. by the coalescence of a series of cells arranged in a linear direction. They are generally Fig. 415.. Tubular shell-structure from external surface of Anomia Ephippium. Magnified 250 diameters. most abundant in shells whose exterior has a foliated or sculptured character; and not un- frequently they may be distinctly seen to pass directly towards the prominences of the sur- face, — as in Lima scabra and various species of Chama. They are by no means restricted, however, to shells thus characterised; nor are they universally present in them. Of the origin and mode of formation of the membranous shell-structure, it is rather diffi- cult to give an exact account. Possibly, after the epidermic cells have undergone calcifica- tion, so as to form the external cellular layer, the basement membrane itself may become detached from the surface of the mantle, in combination with a layer of calcareous matter. Even in nacre, however, which may be con- sidered as the most perfect form of this sub- stance, indications of cellular structure are not unfrequently to be seen, especially in univalve shells : these are particularly evident in Haliotix, the nacreous laminae of which, when carefully examined under a sufficiently high magnifying power, are found to be com- posed of minute cells of a long oval form (fig. 416.), their short diameter not bein<* above l-5000th of an inch. Their boundaries in many parts are very indistinct, or even disappear altogether, so that every gradation can he traced, from the obviously cellular ar- rangement shown in fig. 412., to the homo- geneous aspect presented by the nacre of bivalve shells. The same cellular structure, and the same gradation to a homogeneous stratum, may be made apparent in the decal- cified membrane ; so that here we seem to have evidence that even the membranous shell- substance is originally formed by the agency of cells, although the bou

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• booksubjectanatomy
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