. The microscope and its revelations. outward extension into fringes of gills, each of whichconsists of an arch with straight lamina? hanging down from it, andevery one of these lamina? (fig. 799) is furnished with a double rowof leaflets, which is most minutely supplied with blood-vessels,their network (as seen at A)being so close that its meshes(indicated by the dots in thefigure) cover less space than thevessels themselves. The gills of• fish are not ciliated on theirsurface, like those of molluscsand of the larva of the water-newt, the necessity for such amode of renewing the fluid inconta
. The microscope and its revelations. outward extension into fringes of gills, each of whichconsists of an arch with straight lamina? hanging down from it, andevery one of these lamina? (fig. 799) is furnished with a double rowof leaflets, which is most minutely supplied with blood-vessels,their network (as seen at A)being so close that its meshes(indicated by the dots in thefigure) cover less space than thevessels themselves. The gills of• fish are not ciliated on theirsurface, like those of molluscsand of the larva of the water-newt, the necessity for such amode of renewing the fluid incontact with them being super-seded by the muscular apparatuswith which their gill-chamber isfurnished. But in batrachiansand reptiles the respiratory sur-face is formed by the walls ofan internal cavity, that of thelungs: these organs, however,are constructed on a plan verydifferent from that which theypresent in higher Vertebrate,,the great extension of surfacewhich is effected ill the latter FIG. 799.—Two branchial processes of the. gill of the eel, showing the branchiallamellae : A, portion of one of these pro-cesses enlarged, showing the capillarynetwork of the lamella?. by the minute subdivision ofthe cavity not being here neces-sary. In the frog (for example)the cavity of each lung is un-divided ; its walls, which aivthin and membranous at thelower part, there present asimple smooth expanse; and itis only at the upper part, wherethe extensions of the trachea!cartilage form a network overthe interior, that its surface isdepressed into sacculi whoselining is crowded with blood-vessels (fig. 800). In thismanner a set of air-cells isformed in the thickness of theupper wall of the lung, whichcommunicate with the generalcavity, and very much increasethe surface over which the blood comes into relation with the air ;but each air-cell has a capillary network of its own, which lies011 one side against its wall, so as only to be exposed to the airon its free surface. In the elongat
Size: 1264px × 1977px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
