cenogenesis
n . 新生性变异
新生性变异
cenogenesis n 1 :
introduction during embryonic development of characters or structure not present in the earlier evolutionary history of the strain or species (
such as the addition of the placenta in mammalian evolution ) [
synonym : {
cenogenesis },
{
kenogenesis }, {
caenogenesis }, {
cainogenesis },
{
kainogenesis }] [
ant : {
palingenesis }, {
recapitulation }]
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 ]
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 ]
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 ]
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