Dictionary:

ovum

  (ō'vəm)

The female reproductive cell or gamete of animals; egg.

[Latin ōvum, egg.]

The egg or female sex cell. Strictly speaking, the term refers to this cell when it is ready for fertilization, but it is often applied to earlier or later stages. Confusion is avoided by using qualifying adjectives such as immature, ripe, mature, fertilized, or developing ova. The mature ova are generally spheroidal and large. The number of ova produced at one time varies in different animals, from millions in many marine animals that spawn into the surrounding sea water to about a dozen or less in mammals in which adaptations for internal nourishment of the developing embryo and care of the young are highly developed.

In the ovary the immature ovum is associated with follicle cells through which it receives material for growth. In mammals, as the egg matures, these cells arrange themselves into a structure known as the Graafian, or vesicular, follicle, consisting of a large fluid-filled cavity into which the ovum, surrounded by several layers of cells, projects from the layer of follicle cells that constitutes the inner wall (see illustration). The fluid contains estrogenic female sex hormone secreted by cells in an intermediate layer of the follicular wall.

Section of a mammalian ovary.

Yolk, or deutoplasm, is essentially a food reserve in the form of small spherules, present to a greater or lesser extent in all eggs. It accounts largely for the differences in size of eggs. Eggs are classified according to the distribution of yolk. In the isolecithal type there is a nearly uniform distribution through the cytoplasm, as in most small eggs. The yolk in telolecithal eggs is increasingly concentrated toward one pole, as in the large eggs of fish, amphibians, reptiles, and birds. Centrolecithal, or centrally located, yolk occurs in eggs of insects and cephalopod mollusks. See also Gametogenesis; Oogenesis.

(pl ova) a female germ cell containing 23 chromosomes.

In classical architecture and derivatives, an egg-shaped ornamental motif.

Pl. ova [L.] egg; the female reproductive or germ cell which, after fertilization, is capable of developing into a new member of the same species; sometimes applied to any stage of the fertilized germ cell during cleavage and even until hatching or birth of the new animal.

• centrolecithal o. — one with the yolk concentrated at the center of the egg, surrounded by a peripheral shell of cytoplasm, and with an island of cystoplasm surrounding the nucleus.
• holoblastic o. — one that undergoes total cleavage.
• isolecithal o. — one with a small amount of yolk evenly distributed throughout the cytoplasm.
• meroblastic o. — one that undergoes partial cleavage.
• o. penetration assay — a biological assay using hamster, or other, zona-free ova as the test medium for the penetrating ability of individual samples of semen.
• primitive o., primordial o. — any egg cell very early in its development.
• telolecithal o. — one with a comparatively large amount of yolk massed at one pole.
• o. transplant — an ovum that has been fertilized in utero is recovered from the dam by flushing from the uterus, inspected under the microscope to ensure viability and transferred to the uterus of an estral female. The donor female has usually been superovulated so that a number of ova can be salvaged in the one operation.

Dansk (Danish)
n. - æg, ægcelle

Nederlands (Dutch)
eitje, kiemcel

Français (French)
n. - ovule

Deutsch (German)
n. - Ei, Ovum

Ελληνική (Greek)
n. - (φυσιολ.) ωάριο

Italiano (Italian)
ovulo

Português (Portuguese)
n. - óvulo (m), ovo (m)

Русский (Russian)
яйцо

Español (Spanish)
n. - ovo, óvulo

Svenska (Swedish)
n. - (biol) ägg

中文（简体） (Chinese (Simplified))
卵, 卵形装饰, 卵子

中文（繁體） (Chinese (Traditional))
n. - 卵, 卵形裝飾, 卵子

한국어 (Korean)
n. - 알, 난자, 난형장식

日本語 (Japanese)
n. - 卵, 卵子, 卵細胞

العربيه (Arabic)
‏(الاسم) بيضه‏

עברית (Hebrew)
n. - ‮זרע הנקבה (ביולוגיה), ביצית‬

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