n. A kernel; hence, a central mass about which matter is collected, or to which accretion is made; any body or thing that serves as a center of aggregation or assemblage; figuratively, something existing as an initial or focal point or aggregate: as, a nucleus of truth; a nucleus of civilization.n. In biology, the kernel of a cell, in general; a central or interior differentiated mass of protoplasm, found in nearly all cells, vegetable or animal, and consisting of an oval or rounded body composed ofn. a nuclear membranen. nuclear network, andn. nucleoplasm, and containing nucleoli. The nuclear network is made up of threads or fibrils which are composed of a deeply staining part, “chromatin,” and a feebly staining intermediate substance, “linin” or parachromatin (nucleohyaloplasm). In the meshes of the network is found the more fluid part of the nucleus, the nucleoplasm (achromatin, karyochylema, paralinin). Nucleoplasm, according to Carnoy, consists of a plastin network and a granular fluid, “enchylema.” The nuclear membrane is considered by some observers to be an inner limiting layer of cell-protoplasm surrounding the nucleus, by others to be a condensation of the peripheral portion of the nuclear network. There may be but one nucleus or several nuclei in one cell; and a nucleus may be nucleolate or not. Nuclei are generally proportionate in size to the cell containing them: in some instances, however, they form almost the entire cell mass. A structural difference between the nucleus and the rest of the cell-protoplasm is indicated by its greater resistance to powerful reagents, and by its varied reaction with stains. Functionally, the nucleus is the most important portion of the cell, as it is here that the complex series of changes known as karyokinesis take place, resulting in the division of the nucleus and followed by the division of the cell. This process of mitosic or indirect cell-division is found in all varieties of cells, whether vegetable or animal, fetal or adult, normal or pathological. Instances of cell-division not mitosic have, however, been noted. The nucleus of the human ovum was discovered by Purkinje in 1825, and hence is often called the corpuscle of Purkinje. Its usual name in text-books of anatomy is germinal vesicle. See cut under cell, 5.n. In zoology:n. In ascidians, the alimentary and reproductive viscera collectively, when these are aggregated into a mass, as in the salps.n. In protozoans, a solid rod-like or strap-shaped body, having in many cases the functions of an ovary in connection with a nucleolus (see nucleolus, 2).n. In echinoderms, the madreporiform bodyn. In anatomy, a collection of ganglion-cells in the brain or other portion of the cerebrospinal axis.n. In conchology, the embryonic shell which remains at the apex of the mature shell, as of a gastropod; also, the initial point from which the operculum of a gastropod grows. See protoconch.n. A body having a stronger or weaker attraction for the gas, vapor, or salt of a solution than for the liquid part of it, and therefore modifying by its presence the freezing-and boiling-points.n. In astronomy, the bright central point usually present in the head of a comet and often in a nebula.n. A genus of gastropods: same as Columbella.n. Same as claustrum, 1.n. n. A very small colony of honey-bees started for the purpose of rearing queens to exchange with the queens of full colonies, thus assisting in the prevention of swarming.n. no points at all;n. a perfect set. This result (set) is the nucleus EΩ.
