. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. THE SKIN AND SKELETON. 131 skin, being a net-work of fibrous tissue and earthy matter. It varies in shape from a sphere to a disk, and consists of hundreds of angular pieces accurately fitted together, like mosaic-work. These form ten zones, like the rite of a melon, five broad ones alternating with five narrower. Fig. 97.—Structure of Sea-urchins' Spines: 1, a, spine of Cidaris cut longitudinally; t, s, ball-and-socket joint; p, pedicellarise; 2, 3, trans
. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. THE SKIN AND SKELETON. 131 skin, being a net-work of fibrous tissue and earthy matter. It varies in shape from a sphere to a disk, and consists of hundreds of angular pieces accurately fitted together, like mosaic-work. These form ten zones, like the rite of a melon, five broad ones alternating with five narrower. Fig. 97.—Structure of Sea-urchins' Spines: 1, a, spine of Cidaris cut longitudinally; t, s, ball-and-socket joint; p, pedicellarise; 2, 3, transverse sections of spines of Cidaris and Echinus. ones. The former (called interambulacra) are covered with tubercles bearing movable spines. The narrow zones (called ambulacra, as they are likened to walks through a forest) are pierced with small holes, through which the animal sends out fleshy sucker-feet. The skin of the Crab and Lobster is hardened by cal- careous deposit into a " crust," or shell ;73 but, instead of forming one piece, it is divided into a series of segments, which move on each other. The number of these seg- ments, or rings, is usually twenty-one—to the head, tho- rax, and abdomen, seven each. In the adult, however, the rings of the head and thorax are often soldered to- gether into one shield, called cephalo-thorax; and in the Horseshoe Crab the abdominal rings are also united. The shell of Crustaceans is periodically cast off, for the ani- mals continue to grow even after they have reached their. 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 Orton, James, 1830-1877; Birge, E. A. (Edward Asahel), 1851-1950. New York : Harper & Bros.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1883
