. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Outgo Apparatus 429 materials from the blood stream. When it is remembered that there are over 2,000,000 sweat glands in the skin of an ordinary human being, and that end to end they constitute over twenty-five miles of glandular tubing, according to Macfie, it will be realized that these microscopic structures are by no means insignificant understudies to the kidneys in the disposal of liquid waste materials from the body. For purposes of general descript
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Outgo Apparatus 429 materials from the blood stream. When it is remembered that there are over 2,000,000 sweat glands in the skin of an ordinary human being, and that end to end they constitute over twenty-five miles of glandular tubing, according to Macfie, it will be realized that these microscopic structures are by no means insignificant understudies to the kidneys in the disposal of liquid waste materials from the body. For purposes of general description the urinary apparatus of a typical vertebrate may be considered under three headings: (1) kidneys; (2) uri- nary ducts ; and (3) bladders. II. KIDNEYS I. Forms With respect to the shape of the paired kidneys the evolutionary tend- ency is towards compactness and consequently there is a certain parallel between their form and the general contour of the body. The kidneys of the primitive eel-like cyclostomes are long straplike bands, while in fishes gen- erally they extend not only throughout the length of the body cavity but also they may penetrate even beyond into the tail muscu- lature. Frequently too, the typical shape of the kidneys of fishes is modified to conform to the presence of the swim bladder, which in fishes is a bedfellow of these organs. Among amphibians the wormlike Gymnophiona and the long-bodied urodeles have correspondingly elongated kidneys, narrower anteriorly and widening posteriorly, while in the squat anurans these organs become much more compact and rounded in shape. Fig. 360. Left Although lizards and alligators somewhat resemble lobulated kidney urodeles superficially, the relation between the shape of the ,. ^r' ffr, * r ;' . l dissected. (After kidneys and the form of the body is less marked. The Henle.) kidneys, however, are still somewhat elongated, but in turtles become decidedly compact, conforming to the rigid requirements of space imposed b
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