coenogenesis

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]