. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. 124 COMPARATIVE ZOOLOGY. organs appear, they are constructed upon the same prin- ciple : each consisting of a very thin sheet of tissue sepa- rating the blood to be purified from the atmosphere, and straining out, as it were, the noxious matters. All, more- over, excrete the same substances, but in very different proportions: the lungs exliale carbonic acid and water, with a trace of urea; the kidneys expel water, urea, and a little carbonic acid; while the skin partakes of the nat- ure of both, for it
. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. 124 COMPARATIVE ZOOLOGY. organs appear, they are constructed upon the same prin- ciple : each consisting of a very thin sheet of tissue sepa- rating the blood to be purified from the atmosphere, and straining out, as it were, the noxious matters. All, more- over, excrete the same substances, but in very different proportions: the lungs exliale carbonic acid and water, with a trace of urea; the kidneys expel water, urea, and a little carbonic acid; while the skin partakes of the nat- ure of both, for it is not only respiratory, especially among the lower animals, but it performs the work of the kidneys when they are diseased. 1. The lungs (and likewise gills) are mainly excretory organs. The oxygen they impart sweeps wnth the blood through every part of the body, and unites with, i. e., burns up, the effete matters, which, set free by muscular and nervous exertion, would poison the system, if not removed. The carbonic-acid gas thus generated is car- ried by the veins to the lungs, and there exhaled in bi-eath- ing. This process is more immedi- ately necessary to life than any oth- er: the arrest of respiration is fatal. 2. While the lungs (and skin also, to a slight degree) are sources of gain as well as loss to the blood, the kidneys are purely excretory organs. Their sole function is to eliminate the solid products of decay which can not pass out by the lungs. In Mammals, they are discharged in solution; but from other animals -Section of Hnman ^'^^^ ^^""^^ ^^"^^ ^^^^ excrctiou is Kidney, showing the tuhu- morc or Icss soUd. In Insects, the lar portion, 3, grouped into r , . , cones; 7, the ureter, or out- kiQueys are groups of tubes; in the let of the secretion. i-i^ivrni ,^ higher JMonusks, they are represent- ed by spongy masses of follicles; in Vertebrates, they are. Please note that these images are extracted from scanned page images that may have been di
Size: 1209px × 2067px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectzoology
