. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. 66 COM PA RATI VE I'U YSIOLOG Y. cordance with the diverse circumstances under which ova ma- ture and develop, certain variations in structure, mostly of the nature of additions, pi-osent themselves. Thus, ova may be naked, or provided with one or more cover- ings. Tn vertebrates there are usually two membranes around the protoplasm of the ovum : a delicate covering (Vitelline me
. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. 66 COM PA RATI VE I'U YSIOLOG Y. cordance with the diverse circumstances under which ova ma- ture and develop, certain variations in structure, mostly of the nature of additions, pi-osent themselves. Thus, ova may be naked, or provided with one or more cover- ings. Tn vertebrates there are usually two membranes around the protoplasm of the ovum : a delicate covering (Vitelline membrane) beneath which there is another, which is sieve-like from numerous perforations (zona radiata, or z. pellucida). The egg membrane may be impregnated with lime salts (shell). Between the membranes and the yelk there is a fluid albumi- nous substance secreted by the glands of the oviduct, or by other special glands, which provide proteid nutriment in different physical condition from that of the yelk. The general naked-eye appearances of the ovum may be learned from the examination of a hen's egg, which is one of eAJ. Fiu. 56.—DiagMmmatic section of an unimpregnated fowl's egg (Poster and Balfonr, after AH n Thomson), bl, blastoderm or cicatricula; w. y, whlto yelk; y. y. yel- low yelk; , chalazs; m, Inner layer of shell membrane; ». m, outer layer of shell membrane; ». shell; k, air-Bpace: w. the white of the egg; ». /, vitel- line mcmbrauu; x, the denser albuminous layer lying next the vltellino mem- brane. the most complicated known, inasmuch as it is adapted for development outside of the body of the mother, and must, con- sequently, be capable of preserving its form and essential vital properties in a medium in which it is liable to undei-go loss of water, protected as it now is with shell, etc., but which, the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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Keywords: ., bookauthormillswes, bookcentury1800, bookdecade1890, bookyear1890
