Title: The cat : an introduction to the study of backboned animals, especially mammals
Identifier: catintroduction00miva (find matches)
Year: 1881 (1880s)
Authors: Mivart, St. George Jackson, 1827-1900
Subjects: Cats; Anatomy, Comparative
Publisher: New York : Scribner's
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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chap, x.) THE DEVELOPMENT OF THE CAT. 355 cellular investment, or follicle, around the primordial ova, and ultimately grow into the tunica granulosa within the Graafian vesicle. Sometimes two or more of the ova-forming epithelial cells of a nest, will coalesce and form a large protoplasmic mass with two or more nuclei, and thus a cell may arise and then he nourished by appropriating the substance of other cells. An enlarged epithelial
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Fig. 159.— Portion of the Ovary of a Kitten about Three Weeks old, showing the Germ- epithelium and Primordial Ova. with large Egg-nests more or less sur- rounded by Stroma (Foulis). a. Primordial ova. b. Smaller cells, resulting from the fission of larger epithelial cells, and beginning to form the membrana granulosa. c. Large clusters of germ epithelial cells, large egg-nests. d. Large germ epithelial cells. e. Stroma of ovary. /. Germ epithelial cells. cell, or primordial ovum, when it has become enclosed in a follicle, becomes a " permanent ovum." The protoplasm, or vitellus, accu- mulates about the nucleus or germinal vesicle, which developes a nucleolus, or spot, while the zona pellucid a forms either just within or externally to a delicate membrane investing the vitellus. The ovum, with its epithelial lining and external investment of fibrous vascular stroma, is a " Graafian follicle." At first the ovum itself is closely embraced by the follicle. Afterwards the follicle greatly enlarges, and its contents separate into (1) the cells of the membrana granulosa, lining the vesicle and enclosing (2) a fluid, (3) the ovum, and (4) an aggregation of cells— the discus proligerus—which remains adherent around the ovum. The ovary at first contains thousands of incipient ova, but the great majority disappear as development proceeds. When the kitten is but from two to four weeks old a very large part of the whole ovary consists of egg-clusters, but at five months old there is only a zone of young eggs left immediately beneath the tunica albuginea.* § 17. The nervous system, though a unity in its fully formed condition, is more diverse in its origin than is the alimentary system. The latter system, as has been shown, arises as a groove * See Dr. Foulis, I. c, p. 373. A A 2

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