segmentation defined in 1951 year

segmentation - segmentation;
segmentation - (1) (Zool.). Metammc segmentation, Metamerism. Repetition of a pattern of elements belonging to each of the main organ systems of the body, along the antero-posterior axis of the body; or a comparable repetition along the axis of an appendage. Most strongly marked in Annelida and Arthropoda. The repetition produces a series of units, called segments (or metameres), of fundamentally similar structure, e.g. in the earthworm each of the externally visible rings is a segment; each segment contains a pattern of blood-vessels, epidermal structures, nervous system, excretory organs, etc., which is repeated with some variation in every other segment. It should be noted that the similarity beween different segments of a given animal may be very imperfect. In particular the segments at the anterior end, which form the head, are very different from each other and from other segments. Vertebrates show segmentation most clearly in embryonic development, but it is almost confined to {parts of the muscular, skeletal, and nervous systems. See also: Somitk Mesoderm. It does not appear in the epidermis, as in Annelida and Arthropoda. (2) In embryology, a synonym for cleavage applied to both plants and animals.

near segmentation in Knolik

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