REGENERATION
Regeneration
can be defined as the natural ability of living organism to replace worn out
parts, repair or renew damaged or lost part of the body or to reconstitute the
whole body from a small fragment during post embryonic life of an organism.
Various
degree of ability to regenerate the lost part is seen in animal kingdom. It may
involve replacement of damaged cells healing of wound or a complete replacement
of the organ lost or formation of a complete animal from small fragment.
The capacity
of regeneration is greater in simple animal like sponges, coelenterates,
flatworms, annelids, echinoderms and tunicates. In animals like echinoderms
regeneration is also a mean of asexual reproduction. Among lower vertebrates
the power of regeneration is limited to regeneration of limbs, jaws and tail
while in higher vertebrates it is limited to healing of damaged tissue only.
TYPES: based on cellular mechanism
regeneration can be classified into two types,
1. EPIMORPHOSIS or EPIMORPHIC
REGENERATION: it is the regeneration of lost part of the body by growth and
differentiation of cells by remainder piece of the part.
For example: the salamanders, starfishes, crabs have an ability to
regenerate the limbs within few weeks when lost or amputated. If the tail of a
house lizard is cut or an appendage of crab is cut, the missing part develops
again from the remaining part of the body.
2. MORPHOLAXIS or MORPHOLACTIC
REGENERATION: in this type of regeneration entire animal is regenerated from a
small separated piece of an animal. It involves reorganization of various part
of an organism from few cells to form a new organism. Morpholaxis is seen only
in lower animals.
For example; if a sponge or hydra or planarian is cut into two or more
pieces, each piece will reconstitute itself into a new and complete individual
of a small size.
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