. The chain of life in geological time [microform] : a sketch of the origin and succession of animals and plants. Paleontology; Paleobotany; Paléontologie; Paléobotanique. i THE AGE OF INVERTEBRATES OF THE SEA. 49 sponges may be roughly divided into three groups: 1, those with corneous or horny skeleton, like our common washing sponges; 2, those with skeletons composed of silicious needles of various forms and arrangement; 3, those with calcareous spicules. Of these, the second or silicious group has precedence in point of time, beginning in the Early Cam- brian, and continuing to the present.
. The chain of life in geological time [microform] : a sketch of the origin and succession of animals and plants. Paleontology; Paleobotany; Paléontologie; Paléobotanique. i THE AGE OF INVERTEBRATES OF THE SEA. 49 sponges may be roughly divided into three groups: 1, those with corneous or horny skeleton, like our common washing sponges; 2, those with skeletons composed of silicious needles of various forms and arrangement; 3, those with calcareous spicules. Of these, the second or silicious group has precedence in point of time, beginning in the Early Cam- brian, and continuing to the present. Two of its subdivisions are especially interesting in their range. The first is that of the Lattice-sponges {Hexactinellidce), in vhich the spicules have. Fig. 2g.—Portion of skeleton of Hetactinpllid Sponge {Caeloftychium). Magnified. After Zittel. six rays placed at right angles, and are attached to each other by their points, so as to form a very regular network (Fig. 29). The second is that of the Stone-sponges {LithisfidcB), in which the spicules are four-rayed or irregular, and are united by the branching root-like ends of the rays. The most beautiful of all sponges, the Venus Flower-basket {Euplectelld)^ is a modern E. 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 Dawson, J. W. (John William), Sir, 1820-1899. London : Religious Tract Society
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectpaleontology, bookyea
