. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. 396 physiology and morphology of animals. Illustration of a Fundamental Law of Evolution.—It is a fundamental law of evolution that the phylogenic or evo- lution series is repeated more or less perfectly in the ontogenic or embryonic series, and often also in the taxo- nomic or classification series. An admirable illustration of this is found in the life history of amphibians. We have already seen that the frog in its embryonic development is at first a legless, gill-breathing ani
. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. 396 physiology and morphology of animals. Illustration of a Fundamental Law of Evolution.—It is a fundamental law of evolution that the phylogenic or evo- lution series is repeated more or less perfectly in the ontogenic or embryonic series, and often also in the taxo- nomic or classification series. An admirable illustration of this is found in the life history of amphibians. We have already seen that the frog in its embryonic development is at first a legless, gill-breathing Fig. 274.—Diagram of mammalian heart: a, aorta; p} pulmonary artery ; sc, s'c', subclavium on each side ; c, c\ carotids on each side. The numerals give the ordinal numbers of the arches as in the previous figures. If it stopped there it would be classed as a fish ; but it goes on. It next gets itself legs and an imperfect lung, and breathes now both air and water. If it stopped here it would be classed as a perennibranch ; but it goes on. It next loses its gills and improves its lungs and breathes air only, but retains the tail. If it stopped now it would. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York, D. Appleton and Company
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