182
PAUL BRIEN
sexual phase, give rise to gonia (Chun, 1896; Brien, 1941; Bouillon,
1956).
The identity between blastogenic cells and germinal cells, the reversibility of somatic cells into germinal cells, lends support to the argument
against the concept of the duality of the organism into soma and germ.
The organism is not double. It is a living unit capable of two distinct
physiological conditions, one gametic, the other blastogenic, determining
the direction which an island of cells will be able to take, locally, becoming agamic reproductive cells or gametes.
Germinal tissue obeys a law common to all tissues. In vertebrates,
where regeneration is difficult, limited, or absent, germinal tissue, when
removed, does not regenerate, any more than does the head of a
decapitated animal. It is the same in the higher invertebrates. But in the
invertebrates where regeneration is possible, germinal tissue becomes
reconstituted as well as other tissues. The absence of regeneration of
germinal tissue cannot be a criterion of the supposed unchangeableness
between germ and soma.
A germ line does not preexist in the animal and may never appear. It
forms like every other cell line called "somatic," in its own time and
place, according to the embryonic physiology. It is no more continuous
than any other cell line, but is reconstituted de novo in each generation.
Its differentiation is sometimes very precocious, to the point of being
determined in the unsegmented egg in a cytoplasmic area which is a
presumptive germinal region, and in this case, it is maintained during
the entire life of the animal. On the contrary, it can be very late as well
as temporary, and appear only when organogenesis is completed, to then
become obliterated when the period of sexual reproduction ceases in the
cycle of the animal (Brien, 1926, 1964, 1966).
Differentiation of the germ line is an aspect of organogenesis. It obeys
its kinetics. It is not previous to it and does not precede it; it is a result
of it. The animal reproduces because it lives, grows, and develops.
VI. The Organization of the Bud
The bud, like the egg, shows a polarity, a symmetry which responds
to its organization and is responsible for the ontogenesis of a new blastozooid. Just as for the egg, the polarity and symmetry of the bud depend
on its position in relation to its parent and the resulting physiological
contingencies.
The polarity of the gemmule of the Spongillidae is apparent exteriorly
by the micropyle from which is established the gradient of division of
PAUL BRIEN
sexual phase, give rise to gonia (Chun, 1896; Brien, 1941; Bouillon,
1956).
The identity between blastogenic cells and germinal cells, the reversibility of somatic cells into germinal cells, lends support to the argument
against the concept of the duality of the organism into soma and germ.
The organism is not double. It is a living unit capable of two distinct
physiological conditions, one gametic, the other blastogenic, determining
the direction which an island of cells will be able to take, locally, becoming agamic reproductive cells or gametes.
Germinal tissue obeys a law common to all tissues. In vertebrates,
where regeneration is difficult, limited, or absent, germinal tissue, when
removed, does not regenerate, any more than does the head of a
decapitated animal. It is the same in the higher invertebrates. But in the
invertebrates where regeneration is possible, germinal tissue becomes
reconstituted as well as other tissues. The absence of regeneration of
germinal tissue cannot be a criterion of the supposed unchangeableness
between germ and soma.
A germ line does not preexist in the animal and may never appear. It
forms like every other cell line called "somatic," in its own time and
place, according to the embryonic physiology. It is no more continuous
than any other cell line, but is reconstituted de novo in each generation.
Its differentiation is sometimes very precocious, to the point of being
determined in the unsegmented egg in a cytoplasmic area which is a
presumptive germinal region, and in this case, it is maintained during
the entire life of the animal. On the contrary, it can be very late as well
as temporary, and appear only when organogenesis is completed, to then
become obliterated when the period of sexual reproduction ceases in the
cycle of the animal (Brien, 1926, 1964, 1966).
Differentiation of the germ line is an aspect of organogenesis. It obeys
its kinetics. It is not previous to it and does not precede it; it is a result
of it. The animal reproduces because it lives, grows, and develops.
VI. The Organization of the Bud
The bud, like the egg, shows a polarity, a symmetry which responds
to its organization and is responsible for the ontogenesis of a new blastozooid. Just as for the egg, the polarity and symmetry of the bud depend
on its position in relation to its parent and the resulting physiological
contingencies.
The polarity of the gemmule of the Spongillidae is apparent exteriorly
by the micropyle from which is established the gradient of division of