Segmentation nucleus
Segmentation Seg`men*ta"tion, n. The act or process of dividing into segments; specifically (Biol.), a self-division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster]

{Segmentation cavity} (Biol.), the cavity formed by the arrangement of the cells in segmentation or cleavage of the ovum; the cavity of the blastosphere. In the gastrula stage, the segmentation cavity in which the mesoblast is formed lies between the entoblast and ectoblast. See Illust. of {Invagination}.

{Segmentation nucleus} (Biol.), the body formed by fusion of the male and female pronucleus in an impregnated ovum. See the Note under {Pronucleus}.

{Segmentation of the ovum}, or {Egg cleavage} (Biol.), the process by which the embryos of all the higher plants and animals are derived from the germ cell. In the simplest case, that of small ova destitute of food yolk, the ovum or egg divides into two similar halves or segments (blastomeres), each of these again divides into two, and so on, thus giving rise to a mass of cells (mulberry mass, or morula), all equal and similar, from the growth and development of which the future animal is to be formed. This constitutes {regular segmentation}. Quite frequently, however, the equality and regularity of cleavage is interfered with by the presence of food yolk, from which results unequal segmentation. See {Holoblastic}, {Meroblastic}, {Alecithal}, {Centrolecithal}, {Ectolecithal}, and {Ovum}.

{Segmentation sphere} (Biol.), the blastosphere, or morula. See {Morula}. [1913 Webster]


The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

  • segmentation nucleus — Nucleus formed by union of male and female pronuclei during fertilization …   Dictionary of invertebrate zoology

  • segmentation nucleus — the fertilization nucleus after cleavage has begun. Called also cleavage n …   Medical dictionary

  • Segmentation — Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation cavity} (Biol …   The Collaborative International Dictionary of English

  • Segmentation cavity — Segmentation Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation… …   The Collaborative International Dictionary of English

  • Segmentation of the ovum — Segmentation Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation… …   The Collaborative International Dictionary of English

  • Segmentation sphere — Segmentation Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation… …   The Collaborative International Dictionary of English

  • Nucleus — 1) In cell biology, the structure that houses the chromosomes. 2) In neuroanatomy, a group of nerve cells. * * * 1. In cytology, typically a rounded or oval mass of protoplasm within the cytoplasm of a plant or animal cell; it is surrounded by a… …   Medical dictionary

  • regular segmentation — Segmentation Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation… …   The Collaborative International Dictionary of English

  • cleavage nucleus — segmentation n …   Medical dictionary

  • Egg cleavage — Segmentation Seg men*ta tion, n. The act or process of dividing into segments; specifically (Biol.), a self division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation. [1913 Webster] {Segmentation… …   The Collaborative International Dictionary of English

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”