The microscope and its revelations . re openings leading to sacculi in their substance. But eachof these cavities is surrounded by a soHd plexus of blood-vessels, which does not seem to be covered by any limitingmembrane, but which admits air from the central cavity freelybetvreen its meshes ; and thus its capillaries are in imme-diate relation with air on aU. sides, a provision that is obviouslyvery favoui-able to the complete and rapid aeration of theblood they contain.—In the lung of Man and Mamjuals, again,the plan of structure differs from the foregoing, though thegeneral effect of it is
The microscope and its revelations . re openings leading to sacculi in their substance. But eachof these cavities is surrounded by a soHd plexus of blood-vessels, which does not seem to be covered by any limitingmembrane, but which admits air from the central cavity freelybetvreen its meshes ; and thus its capillaries are in imme-diate relation with air on aU. sides, a provision that is obviouslyvery favoui-able to the complete and rapid aeration of theblood they contain.—In the lung of Man and Mamjuals, again,the plan of structure differs from the foregoing, though thegeneral effect of it is the same. Eor the whole interior isdivided-up into minute air-ceUs, which fi-eely communicatewith each other, and with the ultimate ramifications of theau--tubes into which the trachea (windpipe) subdivides; andthe network of blood-vessels (Eig. 333) is so disposed in thepartitions between these cavities, that the blood is exposed tothe air on both sides. It has been calculated that the number3 b 738 VERTEBRATED ANIMALS. Fig. of these air-cells grouped around the termination of each air-tube in Man, is not less than 18,000; and that the totalnumber in the entire lungs is siv hundred millions. 439. The fol-lowing list of theparts of the bo-dies of Verte-brata, of whichInjected prepara-tions are mostinteresting asMicroscopic ob-jects, may be ofservice to thosewho may be in-clined to applythemselves totheir production.—Alime7itary Ca-nal; Stomach,showing the ori-fices of the gas-tric follicles, andthe rudimentary villi near the pylorus; Small Intestine,showing the villi and the orifices of the follicles of Lieber-kiihn, and at its lower part the Peyerian glands; LargeIntestine, showing the various glandular follicles :—Respira-tory Organs; Lungs of Mammals, Birds, and Reptiles; GiUsand Swunming-bladder of Fish :—Glandular Organs ; Liver,Gall-bladder, Kidney, Parotid:—Generative Organs ; Oviductof Bird and Prog; Mammalian Placenta; Uterine and PoetalCotyledons of Pu
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