File:A text-book on physiology - for the use of schools and colleges - being an abridgment of the author's larger work on human physiology (1866) (14765080381).jpg

Identifier: textbookonphysio00drap (find matches)
Title: A text-book on physiology : for the use of schools and colleges : being an abridgment of the author's larger work on human physiology
Year: 1866 (1860s)
Authors: Draper, John William, 1811-1882
Subjects: Human physiology Physiology
Publisher: New York : Harper & Bros.
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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d to con-tract so as to leave a clear space be-tween it and the zona pellucida. As%a? the passage along the tube is takingplace, the zona assumes a coating ofalbuminous material; this is what is%^ called in birds the white of the egg. ovarian Ovum. It eventually becomes the chorion.Meantime, after the disappearance of the germinal vesi-cle, a new cell, the embryo cell, arises, and this under-goes subdivision or segmentation, an effect in whichthe yolk itself presently becomes involved, each new ordaughter embryo cell so arising assuming a part of theyolk. A constant process of bisection is thus establish-ed, the yolk dividing first into two portions, then intofour, eight, sixteen, etc., each division containing a nu-cleated cell. At this period may be seen the sperma-tozoa involved in the zona pellucida, and, as the processof bisection goes on, the mass assumes a mulberry as-pect, and finally becomes granular. This is, for the mostpart, finished by the time the ovum enters the uterus.
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Segmentation of ovum. Describe Fig. 134. How dqes the mulberry mass arise?is the process of segmentation finished. When 344 THE GERMINAL MEMBRANE. Fig. 135, p. 343, ova of the dog in various stages: a,from the oviduct, half an inch from the uterus, sperma-tozoids being in the pellucid zone, the yolk bisected; 5,cells of tunica granulosa have disappeared, and the yolkis in four segments; c, continued advance in segmenta-tion ; d, the zona has become thicker, and the segmen-tation more complete; e, ovum burst by compression:some of the segments have escaped; each shows a brightspot or vesicle. As the ovum is about to enter the uterus, each por-tion arising from the segmentation of the yolk has be-come a perfect cell. This cell formation having beenaccomplished at the surface of the yolk first, the cellsthere begin to coalesce into a membrane, with an aspectlike that of hexagonal pavement epithelium, and, as thechange passes toward the centre, the cells, as they form,come toward the memb

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