Cenogenesis

4 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Kenogenesis \Ken`o*gen"e*sis\, n. [Gr. ? new + E. genesis.]
     (Biol.)
     Modified evolution, in which nonprimitive characters make
     their appearance in consequence of a secondary adaptation of
     the embryo to the peculiar conditions of its environment; --
     distinguished from {palingenesis}. [Written also


     {cenogenesis} and {c[ae]nogenesis}.]
     [1913 Webster]

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Recapitulation \Re`ca*pit`u*la"tion\
     (r[=e]`k[.a]*p[i^]t"[-u]*l[=a]"sh[u^]n), n. [LL.
     recapitulatio: cf. F. recapitulation.]
     1. The act of recapitulating; a summary, or concise statement
        or enumeration, of the principal points, facts, or
        statements, in a preceding discourse, argument, or essay.
        [1913 Webster]
  
     2. (Zool.) That process of development of the individual
        organism from the embryonic stage onward, which displays a
        parallel between the development of an individual animal
        (ontogeny) and the historical evolution of the species
        (phylogeny). Some authors recognize two types of
        recapitulation, {palingenesis}, in which the truly
        ancestral characters conserved by heredity are reproduced
        during development; and {cenogenesis} ({kenogenesis} or
        {coenogenesis}), the mode of individual development in
        which alterations in the development process have changed
        the original process of recapitulation and obscured the
        evolutionary pathway.
        [PJC]
  
              This parallel is explained by the theory of
              evolution, according to which, in the words of
              Sidgwick, "the developmental history of the
              individual appears to be a short and simplified
              repetition, or in a certain sense a recapitulation,
              of the course of development of the species."
              Examples of recapitulation may be found in the
              embryological development of all vertebrates. Thus
              the frog develops through stages in which the embryo
              just before hatching is very fish-like, after
              hatching becomes a tadpole which exhibits many
              newt-like characters; and finally reaches the
              permanent frog stage. This accords with the
              comparative rank of the fish, newt and frog groups
              in classification; and also with the succession
              appearance of these groups. Man, as the highest
              animal, exhibits most completely these phenomena. In
              the earliest stages the human embryo is
              indistinguishable from that of any other creature. A
              little later the cephalic region shows gill-slits,
              like those which in a shark are a permanent feature,
              and the heart is two-chambered or fish-like. Further
              development closes the gill-slits, and the heart
              changes to the reptilian type. Here the reptiles
              stop, while birds and mammals advance further; but
              the human embryo in its progress to the higher type
              recapitulates and leaves features characteristic of
              lower mammalian forms -- for instance, a distinct
              and comparatively long tail exists. Most of these
              changes are completed before the embryo is six weeks
              old, but some traces of primitive and obsolete
              structures persist throughout life as "vestiges" or
              "rudimentary organs," and others appear after birth
              in infancy, as the well-known tendency of babies to
              turn their feet sideways and inward, and to use
              their toes and feet as grasping organs, after the
              manner of monkeys. This recapitulation of ancestral
              characters in ontogeny is not complete, however, for
              not all the stages are reproduced in every case, so
              far as can be perceived; and it is irregular and
              complicated in various ways among others by the
              inheritance of acquired characters. The most special
              students of it, as Haeckel, Fritz M["u]tter, Hyatt,
              Balfour, etc., distinguish two sorts of
              recapitulation {palingenesis}, exemplified in
              amphibian larvae and {coenogenesis}, the last
              manifested most completely in the metamorphoses of
              insects. Palingenesis is recapitulation without any
              fundamental changes due to the later modification of
              the primitive method of development, while in
              coenogenesis, the mode of development has suffered
              alterations which obscure the original process of
              recapitulation, or support it entirely.
                                                    --Encyclopedia
                                                    Americana,
                                                    1961.
        [PJC]

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  cenogenesis \cen`o*gen"e*sis\ n. [Gr. ? new + E. genesis.]
     (Biol.)
     The introduction during embryonic development of characters
     or structure not present in the earlier evolutionary history
     of the strain or species (as addition of the placenta in
     mammalian evolution); a modified evolution, in which
     nonprimitive characters make their appearance in consequence
     of a secondary adaptation of the embryo to the peculiar
     conditions of its environment; -- distinguished from
     {palingenesis}. [Also spelled {caenogenesis} and formerly
     {kenogenesis}.]
     [WordNet 1.5 + 1913 Webster]

From WordNet (r) 2.0 [wn]:

  cenogenesis
       n : introduction during embryonic development of characters or
           structure not present in the earlier evolutionary history
           of the strain or species (as addition of the placenta in
           mammalian evolution) [syn: {kenogenesis}, {caenogenesis},
            {cainogenesis}, {kainogenesis}] [ant: {palingenesis}]