326
TH. LENDER
supernatant fluid. In this way, they can be extracted from ground-up
heads of Polycelis nigra, Dugesia lugubris, Dugesia gonocephala, and
Dendrocoelum lacteum. The inductive power is not destroyed if the
ground material is lyophilized, or treated with alcohol at 70°, or heated
to 60°. It must be boiled for 30 minutes before its inductive capacity is
lost.
Preparations made by grinding up the tail are normally inactive, but
if they are treated with alcohol or are heated for some minutes at 60°
they become active. Thus it appears that the 'organisines' are present in
the entire planarian body. The brain emits active 'organisines' whereas
in the tail of the planarian these substances are present as inactive
precursors bound to the cell. In regions other than the brain, treatment
of the ground material, then, would unmask the inductive capacity.
I t will not be possible to elucidate the chemical nature of these
substances until biochemical studies have been completed and until a
material has been isolated containing the inductive substances in
abundance.
IV. Conclusion
The morphogenesis of the organs of fresh-water Planaria in regeneration is conditioned by two groups of factors: the presence of regeneration
cells and the different inductive mechanisms.
The demonstration of neoblasts has been facilitated by the use of the
methyl green-pyronine technique. These cells, which are free in the
parenchyma, have RNA-rich cytoplasm and nucleoli, and nuclei containing DNA. They divide actively by mitosis especially during the
early phases of regeneration. They migrate toward zones of injury to
build up the regeneration blastemas in which the organs differentiate.
The regeneration of the principal organs takes place at the expense of
the neoblasts. This has been demonstrated for the epidermis, the
nervous system, the eyes, the genital glands, the copulatory apparatus,
and the pharynx. Some doubt still remains with regard to the digestive
tract, although Kolmayer and Stephan-Dubois (1960) have observed
regeneration of the digestive tract at the expense of neoblasts in
Dendrocoelum lacteum. The neoblasts therefore appear to be omnipotent
cells. The planarian possesses a stock of undifferentiated cells which
have remained in the embryonic state. The neoblasts are capable of
becoming transformed into somatic as well as germinal cells. The theory
of the germ line is not applicable to the fresh-water planarians.
However, our knowledge of the neoblasts is still very fragmentary.
We are ignorant of the nature as well as the mode of action of the
stimulus which sets in motion the process of regeneration, that is, the
division and migration of the regeneration cells.
TH. LENDER
supernatant fluid. In this way, they can be extracted from ground-up
heads of Polycelis nigra, Dugesia lugubris, Dugesia gonocephala, and
Dendrocoelum lacteum. The inductive power is not destroyed if the
ground material is lyophilized, or treated with alcohol at 70°, or heated
to 60°. It must be boiled for 30 minutes before its inductive capacity is
lost.
Preparations made by grinding up the tail are normally inactive, but
if they are treated with alcohol or are heated for some minutes at 60°
they become active. Thus it appears that the 'organisines' are present in
the entire planarian body. The brain emits active 'organisines' whereas
in the tail of the planarian these substances are present as inactive
precursors bound to the cell. In regions other than the brain, treatment
of the ground material, then, would unmask the inductive capacity.
I t will not be possible to elucidate the chemical nature of these
substances until biochemical studies have been completed and until a
material has been isolated containing the inductive substances in
abundance.
IV. Conclusion
The morphogenesis of the organs of fresh-water Planaria in regeneration is conditioned by two groups of factors: the presence of regeneration
cells and the different inductive mechanisms.
The demonstration of neoblasts has been facilitated by the use of the
methyl green-pyronine technique. These cells, which are free in the
parenchyma, have RNA-rich cytoplasm and nucleoli, and nuclei containing DNA. They divide actively by mitosis especially during the
early phases of regeneration. They migrate toward zones of injury to
build up the regeneration blastemas in which the organs differentiate.
The regeneration of the principal organs takes place at the expense of
the neoblasts. This has been demonstrated for the epidermis, the
nervous system, the eyes, the genital glands, the copulatory apparatus,
and the pharynx. Some doubt still remains with regard to the digestive
tract, although Kolmayer and Stephan-Dubois (1960) have observed
regeneration of the digestive tract at the expense of neoblasts in
Dendrocoelum lacteum. The neoblasts therefore appear to be omnipotent
cells. The planarian possesses a stock of undifferentiated cells which
have remained in the embryonic state. The neoblasts are capable of
becoming transformed into somatic as well as germinal cells. The theory
of the germ line is not applicable to the fresh-water planarians.
However, our knowledge of the neoblasts is still very fragmentary.
We are ignorant of the nature as well as the mode of action of the
stimulus which sets in motion the process of regeneration, that is, the
division and migration of the regeneration cells.