nucleus

Synonyms

Nu"cle*us, n.; pl. E. Nucleuses, L. Nuclei. Etym: [L., a kernel, dim. fr. nux, nucis, nut. Cf. Newel post.] 1. A kernel; hence, a central mass or point about which matter is gathered, or to which accretion is made; the central or material portion; -- used both literally and figuratively. It must contain within itself a nucleus of truth. I. Taylor. 2. (Astron.) Defn: The body or the head of a comet. 3. (Bot.) (a) An incipient ovule of soft cellular tissue. (b) A whole seed, as contained within the seed coats. 4. (Biol.) Defn: A body, usually spheroidal, in a cell or a protozoan, distinguished from the surrounding protoplasm by a difference in refrangibility and in behavior towards chemical reagents. It is more or less protoplasmic, and consists of a clear fluid (achromatin) through which extends a network of fibers (chromatin) in which may be suspended a second rounded body, the nucleolus (see Nucleoplasm). See Cell division, under Division. Note: The nucleus is sometimes termed the endoplast or endoblast, and in the protozoa is supposed to be concerned in the female part of the reproductive process. See Karyokinesis. 5. (Zoöl.) (a) The tip, or earliest part, of a univalve or bivalve shell. (b) The central part around which additional growths are added, as of an operculum. (c) A visceral mass, containing the stomach and other organs, in Tunicata and some mollusks.