(astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail
a small group of indispensable persons or things
a part of the cell containing DNA and RNA and responsible for growth and reproduction
the central structure of the lens that is surrounded by the cortex
any histologically identifiable mass of neural cell bodies in the brain or spinal cord
A kernel; hence, a central mass or point about which matter is gathered, or to which accretion is made; the central or material portion;
The body or the head of a comet.
An incipient ovule of soft cellular tissue.
A whole seed, as contained within the seed coats.
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.
The tip, or earliest part, of a univalve or bivalve shell.
The central part around which additional growths are added, as of an operculum.
A visceral mass, containing the stomach and other organs, in tunicata and some mollusks.