. Juvenile Instructor. osesin the world: their shells are prized asornaments and are valuable in the arts,the beautiful mother of pearl is a pro-duct of the oyster, and the Tyrianpurple, which in ancient times was re-served as a color for the robes of royaltyalone, was obtained from these bodies of moliusks serve as food formany larger animals, and some of themsuch as oysters, clams, and scallops areeaten by human beings. In number of individuals and varietyof form the moliusks surpass all otherdivisions of the animal kingdom exceptthat of the insects. Of living moliusks,twenty tho
. Juvenile Instructor. osesin the world: their shells are prized asornaments and are valuable in the arts,the beautiful mother of pearl is a pro-duct of the oyster, and the Tyrianpurple, which in ancient times was re-served as a color for the robes of royaltyalone, was obtained from these bodies of moliusks serve as food formany larger animals, and some of themsuch as oysters, clams, and scallops areeaten by human beings. In number of individuals and varietyof form the moliusks surpass all otherdivisions of the animal kingdom exceptthat of the insects. Of living moliusks,twenty thousand species are known,and of fossil kinds nineteen to this great variety, and to thecomparative ease with which specimensmay be preserved, moliusks have alwaysbeen regarded as a favorite subject forthe student of natural histor\-. 434 THE JUVENILE INSTRUCTOR. According to the presence or absenceof a shell, and to the shape of thiscovering, mollusks are known as(1) Bivahcs, with shells consisting of two. Figure 1. Sepiirate valves of fresh-watermussel,—a bivalve. corresponding parts, which fit togetherclosel), as in the case of the river mussel(figure 1); (2) Univalves possessing ashell composed of one continuous piece;such as the snail (figure 2); and (3)shell-less mollusks, inwhich a tough skinreplaces the shell,such as the gardenslug (figure 3). The shell has beenregarded by man}-people as the skeleton of the mollusk,corresponding to the bones of verte-brate animals; luit there are many great
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Keywords: ., bookauthorgeorgequaylecannon182, bookcentury1800, bookdecade1890
