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PAUL BRIEN
quently, may be as varied as the zoological groups producing it. As a
matter of fact, ontogenesis from such an agamic unit or bud is an aspect
of regeneration which has always presented a challenge to the most eminent biologists. Even if asexual reproduction and regeneration present the
same problems of organogenesis and if the solutions found for one will
apply to the other, still they must not be confused with each other.
Regeneration is a process of organogenesis by "completivity"; some injured animals, cut accidentally or as a result of experiments or a noxious
environment, have the ability to repair their wounds and reestablish
their normal structure. Asexual reproduction is, in addition, propagation
and multiplication. It implies the natural, spontaneous isolation of a
fragment of the parent organism, which, from then on, is able to develop
into an individual similar to the species from which it came. The capacity
for organogenesis in asexual reproduction is sometimes more extensive
than in the case of regeneration and may become even total ontogenesis.
The blastozooids produced by asexual reproduction can develop while
remaining attached to the parent stock. Thus a more or less important
colony is formed. In other cases the blastozooid separates from the parent.
Asexual reproduction is, then, a spreading, a propagation.
The detachment of the agamic unit or budding is accomplished by
scissiparity, strobilation, or gemmiparity (external and internal buds):
statoblasts and gemmules of sponges; buds, sorites, and frustules of
coelenterates; buds and statoblasts of bryozoans; and buds of tunicates.
Actually many intermediate stages form connecting links between the
different types of budding.
Therefore, blastogenesis has two aspects. The one is colonial, consisting
of a sort of expansion and multiplication of the original individual, often
the oozooid; this is the blastogenesis of enlargement or growth. The other
form is the blastogenesis of propagation or dissemination.
In a single species asexual reproduction sometimes alternates with
sexual reproduction: the oozooid reproduces exclusively by budding; only
the resulting blastozooids are sexual. In any case, asexual reproduction
consists of multiplication of the oozooid, resulting in intensification of
sexual reproduction. Asexual reproduction is delayed polyembryony.
II. Blastogenic Localization—Physiological Isolation
Whether blastogenesis is an enlargement and, consequently, colonial,
or whether it is a dissemination and propagation, it is a result of growth,
just as much as is sexual reproduction. In fact, it is an expression of
growth.
PAUL BRIEN
quently, may be as varied as the zoological groups producing it. As a
matter of fact, ontogenesis from such an agamic unit or bud is an aspect
of regeneration which has always presented a challenge to the most eminent biologists. Even if asexual reproduction and regeneration present the
same problems of organogenesis and if the solutions found for one will
apply to the other, still they must not be confused with each other.
Regeneration is a process of organogenesis by "completivity"; some injured animals, cut accidentally or as a result of experiments or a noxious
environment, have the ability to repair their wounds and reestablish
their normal structure. Asexual reproduction is, in addition, propagation
and multiplication. It implies the natural, spontaneous isolation of a
fragment of the parent organism, which, from then on, is able to develop
into an individual similar to the species from which it came. The capacity
for organogenesis in asexual reproduction is sometimes more extensive
than in the case of regeneration and may become even total ontogenesis.
The blastozooids produced by asexual reproduction can develop while
remaining attached to the parent stock. Thus a more or less important
colony is formed. In other cases the blastozooid separates from the parent.
Asexual reproduction is, then, a spreading, a propagation.
The detachment of the agamic unit or budding is accomplished by
scissiparity, strobilation, or gemmiparity (external and internal buds):
statoblasts and gemmules of sponges; buds, sorites, and frustules of
coelenterates; buds and statoblasts of bryozoans; and buds of tunicates.
Actually many intermediate stages form connecting links between the
different types of budding.
Therefore, blastogenesis has two aspects. The one is colonial, consisting
of a sort of expansion and multiplication of the original individual, often
the oozooid; this is the blastogenesis of enlargement or growth. The other
form is the blastogenesis of propagation or dissemination.
In a single species asexual reproduction sometimes alternates with
sexual reproduction: the oozooid reproduces exclusively by budding; only
the resulting blastozooids are sexual. In any case, asexual reproduction
consists of multiplication of the oozooid, resulting in intensification of
sexual reproduction. Asexual reproduction is delayed polyembryony.
II. Blastogenic Localization—Physiological Isolation
Whether blastogenesis is an enlargement and, consequently, colonial,
or whether it is a dissemination and propagation, it is a result of growth,
just as much as is sexual reproduction. In fact, it is an expression of
growth.