. Animal studies. ADAPTATIONS 305. birds, such as the chicken, the duck, and the auk, as with the reptiles, the young animal is hatched with well-devel- oped muscular system and sense organs, and is capable of running about, and, to some extent, of feed- ing itself. Birds of this type are known asprcecocial (Fig. 172), while the name altricial (Fig. 173) is ap- plied to the more highly organized forms, such as the thrushes, doves, and song-birds generally. With these the young are hatched in a wholly helpless condition, with in- effective muscles, deficient senses, and dependent wholly upon th
. Animal studies. ADAPTATIONS 305. birds, such as the chicken, the duck, and the auk, as with the reptiles, the young animal is hatched with well-devel- oped muscular system and sense organs, and is capable of running about, and, to some extent, of feed- ing itself. Birds of this type are known asprcecocial (Fig. 172), while the name altricial (Fig. 173) is ap- plied to the more highly organized forms, such as the thrushes, doves, and song-birds generally. With these the young are hatched in a wholly helpless condition, with in- effective muscles, deficient senses, and dependent wholly upon the parent. The altricial condition de- mands the building of a nest, the establishment of a home, and the Fig. 175.—Esrg-case of California j_« n _e -u £ barn-door"skate (RajaMnocu- continued care of one or both of lata) cut open to show young the parents. inside. (Young issues natu- mi -, -, -\ rally at one end of the case.) The Vei7 l°west mammals known, the duck-bills (Monotremes) of Australia, lay large eggs in a strong shell like those of a turtle, and guard them with great jealousy. But with almost all mammals the egg is very small and without much food-yolk. The egg begins its development within the body. It is nourished by the blood of the mother, and after birth the young is cherished by her, and fed by milk secreted by specialized glands of the skin. All these features are adaptations tending toward the preservation of the young. In the division of mammals next lowest to the Monotremes- kangaroo, opossum, etc.—the young are born in a very im- mature state and are at once seized by the mother and. 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 Jordan, David Starr, 1851-1931; Kellogg, Vernon L. [from old catalog].
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Keywords: ., bookauthorjordanda, bookcentury1900, bookdecade1900, bookyear1903
