ovum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The female reproductive cell or gamete of animals; egg.

Century Dictionary and Cyclopedia

1. n. An egg, in a broad biological sense; the proper product of an ovary; the female germ or seed, which when fertilized by the male sperm, and sometimes without such fecundation, is capable of developing into an individual like the parent. There is agreat similarity in the ova of different animals throughout the metazoic series, from the sponge to the human being, no ova in their early stages being distinguishable from one another in their essential characters. All true ova, as distinguished from spores and products of fission or gemmation, are referable to the single morphological type of the cell; and they are furthermore indistinguishable from unicellular animals, and from many of the cells composing the bodies of the higher animals. An ovum consists of a quantity of protoplasm or cell-substance called the vitellus or yolk, inclosed in a cell-wall or vitelline membrane, and provided with a nucleus and usually a nucleolus; it is engendered in the ovarium, usually in an ovisac or so-called Graafian follicle, is discharged from itsmatrix, usually then meeting with the male element, and proceeds to develop within or without the body of the parent. The ovum proper. like most cells, is usually of microscopic size; but its bulk may be enormously increased by the addition of extrinsic or adventitious protoplasmic or albuminous substance, and it may be further protected by various kinds of egg-pod or egg-shell, all without losing its essential character as a cell. The largest ova, relatively and absolutely, are birds' eggs, these being by far the largest cells known in the animal kingdom. Here the quantity of food-yolk which does not undergo transformation into the body of the chick is out of all proportion to the formative yolk proper, which makes only a speck in the great ball of “yellow” and “white.” Such ova are called meroblastic, in distinction from holoblastic. The human ovum is very minute, relatively and absolutely, averaging about of an inch in diameter. It is said to have been first recognized by K. E. von Baer in 1827. The parts of the ovum have been badly named, without reference to its morphology as a cell. Thus, the cell-wall is called the zona pellucida; the nucleus is named the germinal vesicle or vesicle of Purkinje, and its nucleolus the germinal spot or spot of Wagner. The phrases germinal vesicle and germinal spot are misleading. The first stages of development of an ovum, consequent upon fertilization, consist in the segmentation of the vitellus, or yolk-division, by which the cell-substance becomes a mulberry-mass of spherules, called the morula. The rest is an intricate process of differentiation and specialization of these spherules, and their multiplications into the myriads of different kinds of cells of which the whole body of most adult animals is fabricated. Some of the early special stages of this process are known as the morula, gastrula, blastula, etc. The first tissue or coherent layer of cells produced is called a blastoderm. When there are two layers, inner and outer blastodermic layers, they are distinguished as endoderm and ectoderm; when a third intermediate layer is formed, it is the mesoderm. An ovum is called, in general, a germ until the rudiments of its specific characters appear, when it becomes an embryo, and later may be a fetus. That department of ontology which treats of the development of the ovum is embryology. See cuts under diphyzoöid, gastrulation, gonophore, and ovotestis.
2. n. [capitalized] In conchology, same as Ovulum.
3. n. [capitalized] In ichthyology, a genus of fishes.
4. n. In architecture, an ornament in the shape of an egg.

Wiktionary

1. n. cytology The female gamete in animals; the egg cell.

GNU Webster's 1913

1. n. (Biol.) A more or less spherical and transparent cell, which by a process of multiplication and growth develops into a mass of cells, constituting a new individual like the parent; an egg, spore, germ, or germ cell. See Illust. of mycropyle.
2. n. (Arch.) One of the series of egg-shaped ornaments into which the ovolo is often carved.

WordNet 3.0

1. n. the female reproductive cell; the female gamete