File:Image from page 205 of "Introduction to zoology; a guide to the study of animals, for the use of secondary schools;" (1900) (14804878163).jpg

Identifier: introductiontozo00dave Title: Introduction to zoology; a guide to the study of animals, for the use of secondary schools; Year: 1900 (1900s) Authors: Davenport, Charles Benedict, 1866-1944 Davenport, Gertrude Anna Crotty, 1866- Subjects: Zoology Publisher: New York, Macmillan company London, Macmillian and co., ltd. Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: ghtup to the surface are then examined for pearls. The pearlis the secretion of the oyster about a small foreign body, such as a grain of sand.This secretion prevents theirritant from injuring thetissues. It is of the samenature as the substance lin-ing the shell. The latteris the mother of pearl ofcommerce, and is used forknife handles, buttons, andthe like. The iridescence FIG. 173. —Pectenirradians,scallop, is not due to the chemical left or upper valve. Nat. size, composition of the secreted Photo, by AV. H. C. P. substance, but to the fact that it is deposited so as to leave fine lines on the surfacewhich diffract the light. The Pectinidael include the scallop-shells. These occuralong our whole coast. They live in shallow water, andare capable of rapid movement in the water by clappingthe valves. The adductor muscle of the valves alone iseaten by man. The common species is Pecten irradians.It varies greatly in color, from bluish to reddish andorange (Fig. 173). 1 pecten, coinb.

Text Appearing After Image: THE FUEMl-WATER CLAM AND ITS ALLIES 187 The Ledidae include certain elongated shells with ashiny epidermis, and a large number of teeth on the hinge,which are found chiefly in mud in rather deep water.The animal has a large foot(Fig. 174) with which it bur-rows rapidly. It can alsomove rapidly through thewater as the scallops do. The Ostreidae : include theoysters, which are the mostimportant invertebrate foodfishery, being valued attwenty to thirty million dollars per year for our Atlanticseaboard. Oysters are found on all coasts. Our Ostrea vir-giniana2 extends from the Gulf of St. Lawrence to the Gulfof Mexico. The o}rsters of our Western coast are not soimportant as the Atlantic species. 0. edulis is the prin-

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