The Cambridge natural history . tone aredf^ed p. 483), and does not use its long in Loch Fyne. The topmost pedicle to adhere to any fixed ol)ject.^ •^i^^ ^ ^^ ^ i^™^^- The outline of the shell varies extremely. It may be almostround or prolonged along either axis; the edges of the valvesmay be sniocjth or fluted in correspondence with the ridges andgrooves of tlie outside of the shell. (3n tlie inner surface of the shell of the Testicardinate Brachio-poda., at the hinder end of tlie ventral valve, are two lateralteeth, which fit into corresponding s(jckets in the dorsal form a hing
The Cambridge natural history . tone aredf^ed p. 483), and does not use its long in Loch Fyne. The topmost pedicle to adhere to any fixed ol)ject.^ •^i^^ ^ ^^ ^ i^™^^- The outline of the shell varies extremely. It may be almostround or prolonged along either axis; the edges of the valvesmay be sniocjth or fluted in correspondence with the ridges andgrooves of tlie outside of the shell. (3n tlie inner surface of the shell of the Testicardinate Brachio-poda., at the hinder end of tlie ventral valve, are two lateralteeth, which fit into corresponding s(jckets in the dorsal form a hinge, which in many cases is so arranged as topermit the shell to be opciRMl to only a very limited are also certain ])latc-l!k(! ])rocesses whicli ]irojcct into thelumen of the shell, and hcl]) to sup])ort various portions oftill, body ; and in TrrcJimtula, WahlJiriinia, etc., these Ibrm acomplicated band-like looj), whicli increases in complexity withadvancing age, and serves t(j suppoit the arms. In the extinct. 468 RECENT BRACHIOPODA chap. Spirifera the internal skeleton takes the form of two spirallycoiled lamellae, which almost entirely fill the cavity of the shell;the apices of the spirals point outwards (Fig. 330). The innersurface of the shell also bears the marks of the insertion of thenumerous muscles which govern its movements. Microscopic examination of thin sections of the shell showsthat it consists of small prisms or spicules of calcareous sub-stance, whose long axis lies, roughly speaking, at right angles tothe surface of the shell. These spicules are held together byan organic matrix, in which, however, no cellular elements canbe detected. In sections made through a decalcified shell theposition of the spicules which have been dissolved by the acid isindicated by spaces, and the matrix remains as a network of fibrils,which end on the outside in a thin cuticular layer of organicmatter. In Lingula and JDiscina the organic matter takes amuch larger
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
