File:Kirkes' handbook of physiology (1907) (14789882463).jpg

Identifier: kirkeshandbookof00kirk (find matches)
Title: Kirkes' handbook of physiology
Year: 1907 (1900s)
Authors: Kirkes, William Senhouse, 1823-1864 Greene, Charles Wilson, 1866-1947
Subjects: Physiology
Publisher: New York, W. Wood and company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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males of thiscountry and others of about the same latitude is from fourteen to fifteen:but it is much influenced by the kind of life to which girls are subjected, beingaccelerated by habits of luxury and indolence, and retarded by contrary con-ditions. Its appearance may be slightly earlier in persons dwelling in warmclimates than in those inhabiting colder latitudes. The menstrual functionscontinue through the whole fruitful period of a womans life, and usuallycease between the forty-fifth and fiftieth years, which time is known as theclimacteric. Menstruation does not usually occur in pregnant women. CHAPTER XVII DEVELOPMENT Changes Which Occur in the Ovum Prior to Impregnation. The ovum when ripe and detached from the ovary is a single cell enclosed withinthe zona pellucida, and containing the germinal vesicle and germinal spot.The ovum undergoes a series of changes preparatory to fertilization, knownas maturation, the general effect of which is to reduce the chromatin in anticipa-
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Fig. 499.—The Maturation of theOvum; Extrusion of the Polar Bodies. (Diagrannu itic.)A, An ovum at the commencement of the process; B, after the formation of the spindle. Thechromosomes are gathered at the equator of the spindle. C, One apex of the spindle has pro-jected into a bud on the surface, and half of the divided dyads have passed to each pole; D, theseparation of the first polar body; E, the commencement of the second polar body; F, the comple-tion of the second polar body. (Cunningham.) tion of the added chromatin from the sperm nucleus. The primary changeobserved in the ovum consists in the migration of the germinal vesicle or nucleusto the surface, and the disappearance of its nuclear membrane, with a con-sequent indistinctness of its outline. Its protoplasm becomes to a consider-able extent confounded with the yolk substance, and its germinal spot dis-appears. The next step in the process is the appearance in the yolk of two 691 692 DEVELOPMENT centrosomes in a clear sp

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