. Juvenile Instructor. ve; the central ones are the cardinalteetli, the side ones the lateral teeth. The/;/«,!,•(? lii^aincnt (h) tends by its elasticityto open the valves; in some species theligament is situated within the shell, andacts by expansion, in others it is outsideand operates by contraction. This ten-dency to open the shell is controlled bythe action of stout internal muscles:when-ever this muscular effort is thevalves open; therefore dead bivalvesare always found open. Marks on theshell (a and p) indicate the attachmentof the ailtliiitor miiseles. The /<allial lineP in
. Juvenile Instructor. ve; the central ones are the cardinalteetli, the side ones the lateral teeth. The/;/«,!,•(? lii^aincnt (h) tends by its elasticityto open the valves; in some species theligament is situated within the shell, andacts by expansion, in others it is outsideand operates by contraction. This ten-dency to open the shell is controlled bythe action of stout internal muscles:when-ever this muscular effort is thevalves open; therefore dead bivalvesare always found open. Marks on theshell (a and p) indicate the attachmentof the ailtliiitor miiseles. The /<allial lineP indicates the attachment of the mantle, and runs parallel with the edge of the shell. The body of the animal itself, whichlies within the shell, next claims ourattention. Let us select for examina-tion a good specimen of our commonoyster; carefully remove one valve bysevering the adductor muscles and thehinge ligament, and cut away a portionof the mantle. The illustration, figure5, shows us in diagrammatic form what. P^igure 5. Diagram of tlie body of the oyster{Ostrearirrjiniantt). O, mouth region; M, fringeof mantle; G, lamellate gills; 11, heart; V,region of valve hinge. The direction of thewater as it enters the cavity within themantle is indicated by the arrows. is thus revealed. Over four hundredliving species of oysters are known, andmore than fourteen hundred fossil mollusks increase rapidly, asingle female often depositing duringthe spawning season of two monthsover a million eggs. Such as survivethe depredations of fishes and otherpredaceous creatures, among whichyoung oysters seem to be a delicacy,pass through a three years course ofgrowth before they reach maturity,during which time they remain attachedto fixed objects, such as stones on thebottom, or poles standing in the 0 shows a group of oysters ofmany different sizes so are now recognized as a valu-able article of human food; and theirculture and sale constitute an imp
Size: 1796px × 1391px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorgeorgequaylecannon182, bookcentury1800, bookdecade1890
