. L'élevage des animaux. Les chevaux, le bétail. La reproduction 25. Fig. 6. - Sections à ovarj- de rat, typique de la structure de l'ovaire chez les mammifères. tissu dans la forme d'un tubule. Fvventually heeomes coiistrieted ce sac 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 élaborés. La partie de la follicule de Graaf pas pi-

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. The breeding of animals. Horses; Livestock. REPRODUCTION 25. Fig. 6. — Sections through ovarj- of rat, typical of ovarian structure in mammals. tissue in the form of a tubule. Fvventually this sac heeomes coiistrieted 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- oped. The part of the Graafian follicle not occu- pied by the ovum is filled with a fluid 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 hberating the enclosed egg. The bursting of a Graafian follicle and the discharge of the Qgg is called ovulation. This event is marked by certain phenomena indicating increased sexual activity. It is believfed that menstruation or the period of heat in domestic animals is coextensive with the ripening of the e^gg. 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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