. L'élevage des animaux. Le bétail. La reproduction de tissus 25 sous la forme d'un tubule. Éventuellement, ce sac devient limitée à la surface de l'ovaire jusqu'à ce que finalement l'ouverture extérieure est entièrement fermée et le tubule proximal devient un follicule fermé dans les tissus de l'organe. Dans le follicule lui-même, il a été formé, dans l'intervalle, seul, de grandes cellules sphériques (cellules germinales primordiales-) à partir de laquelle l'un ou parfois deux ovules sont devel- .0--^:k oped. La partie de la déclaration des^^^ follicule de Graaf pas ^- ig. 6. - Sections à pied par l'ovaire fécondé est rempli de rat, typique d'ovules

• Contributeur: Library Book Collection / Alamy Banque D'Images
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. The breeding of animals. Livestock. REPRODUCTION 25 tissue in the form of a tubule. Eventually this sac becomes constricted at the surface of the ovary until finally the external opening is entirely closed and the tubule becomes a closed follicle within the tissues of the organ. Within the follicle itself, there have been formed, in the meantime, single, large spherical cells (primordial germ-cells) from which one or some- times two ova are devel- .0-~^-:k oped. The part of the t^^^ Graafian follicle not OCCU- ^ig. 6. — Sections through ovary pied by the ovum is filled of rat, typical of ovarian structure in • , i n 'A u X mammals. With a nuid substance. The follicle increases in size and approaches the center of the ovary until near maturity, when it rises to the surface and finally is ruptured, thus liberating the enclosed egg. The bursting of a Graafian follicle and the discharge of the egg is called ovulation. This event is marked by certain phenomena indicating increased sexual activity. It is believed that menstruation or the period of heat in domestic animals is coextensive with the ripening of the egg. It is true, however, that, under some circum- stances, ovulation may occur before or after the period of heat. The ripening of the first Graafian follicle in general marks the beginning of. puberty, but has been known to occur even in infancy. In animals generally ovulation does not occur during pregnancy, but there are numerous exceptions to this rule, as will be described later in the case of some animals which have come in heat and have even conceived again, although pregnant at the time (Fig. 7).. 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 work.. Mumford, F. B. (Frederick Blackmar), 1868-1947. New York, Macmillan

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