. Readings in evolution, genetics, and eugenics. Evolution; Heredity; Eugenics. THE RECAPITULATION THEORY 177 At a later stage most of the gill-pouches have been obliterated, but one is retained and converted into the Eustachian canal, which connects the throat with the middle ear, inside of the ear-drum. Similarly, the embryological evidence shows that the lungs of air-breathers have been derived from the swim-bladder of fishes, a conclusion which had already been reached by comparative anatomy, for in a remarkable. Fig. 39.—Embryos in corresponding stage of development of shark {A), fowl (B)
. Readings in evolution, genetics, and eugenics. Evolution; Heredity; Eugenics. THE RECAPITULATION THEORY 177 At a later stage most of the gill-pouches have been obliterated, but one is retained and converted into the Eustachian canal, which connects the throat with the middle ear, inside of the ear-drum. Similarly, the embryological evidence shows that the lungs of air-breathers have been derived from the swim-bladder of fishes, a conclusion which had already been reached by comparative anatomy, for in a remarkable. Fig. 39.—Embryos in corresponding stage of development of shark {A), fowl (B), and man (C); g, gill slits. (From Scolt.) group, known as the Dipnoi or lung-fishes, the air-bladder is utilized for purposes of respiration. It has been objected that, while embryology may prove relation- ship within a single type, it fails to demonstrate any connection between different types, but this is not altogether true. The Tuni- cata, a curious group of marine animals once referred to the Mollusca, are shown by their ontogeny to be related to the vertebrates and the same is true of certain marine worms (Balanoglossus). Indeed, most modem zoologists have adopted a scheme of classification, in which. 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 Newman, Horatio Hackett, b. 1875. Chicago : University of Chicago Press
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