The royal natural history (1893) (14779367944)

Identifier: royalnaturalhist612lyde (find matches)

Title: The royal natural history

Year: 1893 (1890s)

Authors: Lydekker, Richard, 1849-1915 Sclater, Philip Lutley, 1829-1913 Frostick, W. B., former owner. DSI Brooks, W. T., former owner. DSI

Subjects: Zoology Natural history

Publisher: London and New York : Frederick Warne & Co.

Contributing Library: Smithsonian Libraries

Digitizing Sponsor: Smithsonian Libraries

Text Appearing Before Image:

development OP Sycon raphanus (all figures enlarged). parts of the world. They are almost confined to shallow water, the greatest depthfrom which they have been obtained being four hundred and fifty fathoms.Calcareous sponges prefer shade and avoid light, and are chiefly found in caves,under stones, in shells, or in the shade of dense thickets of seaweed. Six-Rayed, or Glass-Sponges,—Class Hexactinellida. In the sponges of this group the skeleton is built of spicules with three axesand six rays, intersecting one another at right angles through a common centre.A second characteristic consists in the comparatively simple arrangement and large

Text Appearing After Image:

GLASS SPONGES. GLASSY GROUP. 537 size of the thimble-shaped flagellated chambers, which attain an average lengthot dso of an inch in Euplectella. Leaving out of consideration the skeleton, thesoft tissues typically form a tubular sac open at the top, and, with the walls, formedof five layers, an outer dermal and an inner gastral membrane with a layer offlagellated chambers suspended between and supported by subdermal and sub-gastral networks of fibres ; the direction of the water current being always from thedermal to the gastral surface. The six-rayed spicule is the form best adapted to SILICEOUS SPICULES OF SIX-EAYED, OR GLASS-SPONGES ; IN THE CENTRE AN EIGHT-SIDED INTERSECTIONNODE OF A FOSSIL VENTRICDLITE SPONGE. support a soft walled sac of this description, one axis being vertical to the walls,and the other two tangential; the rays of each spicule uniting with those of adjoin-ing spicules to form a framework. The typical spicule has six equal rays at rightangles to each other, wi

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1893

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