. The bird, its form and function. Birds. 474 The Bird of this is emphasized in the development of the embryo, during which process a number of additional ribs dis- appear. The aborti^-e ribs of the neck-bones are especially noticeable during the egg-life of the bird, so that in some species we can make out traces of as man\' as fifteen ribs all told. On page 97 a short account was given of the origin of the wings and feet, in the case of the chick—from a primi- tive fin-fold in some general- ized aquatic ancestor. About the fourth day of incuba- tion, sections of our embryo chick wall show a
. The bird, its form and function. Birds. 474 The Bird of this is emphasized in the development of the embryo, during which process a number of additional ribs dis- appear. The aborti^-e ribs of the neck-bones are especially noticeable during the egg-life of the bird, so that in some species we can make out traces of as man\' as fifteen ribs all told. On page 97 a short account was given of the origin of the wings and feet, in the case of the chick—from a primi- tive fin-fold in some general- ized aquatic ancestor. About the fourth day of incuba- tion, sections of our embryo chick wall show a low, round- ed ridge, extending the whole length from the neck to the tail. While we can never be absolutely certain that perfect homology exists between the two, yet it is very significant that soon after its develop- ment it dwindles away, leav- ing four conical, isolated buds—the beginnings of the limbs of the bird. Within two or three da}'s after the appearance of the limbs, faint streaks l^ecome visible upon the tips of the extremities, and these hints of the bones of fingers and toes, for such they are, soon push out beyond the edge, still bound together by their transparent membrane, and for some time they present the appearance of webbed paws or. Fig. -367.—Early embryo of Canada riocse, showing fin-like 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 Beebe, William, 1877-1962. New York, Holt
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
