312
TH. LENDER
retarded and often incomplete. The region of the body situated behind
the fundus of the pharynx is incapable of regenerating a head.
Stephan-Dubois and Kolmayer (1959) investigated the reason for this
deficiency. Methyl green-pyronine staining showed that neoblasts were
present in the pharyngeal and postpharyngeal region (Stephan-Dubois,
1961). The inability of the postpharyngeal region to regenerate the head,
therefore, was not attributable to the absence of neoblasts. If the prepharyngeal region was irradiated after decapitation, the neoblasts of the
region which could form a head blastema, were destroyed. But after a
certain time had elapsed, a head blastema did form by accumulation of
healthy neoblasts which had migrated from the postpharyngeal region
across the irradiated zone. The neoblasts of the postpharyngeal region
which were incapable of forming a head if the part anterior to the fundus
of the pharynx was removed, could do so if they were forced to move to
the anterior region. The inability of the postpharyngeal region to regenerate a head, then, was not due to the absence or different quality of
the neoblasts but, without doubt, to factors which inhibited their power
of regeneration in the postpharyngeal region itself (Kolmayer and
Stephan-Dubois, 1960).
III. Differentiation Factors
The later evolution of a regeneration blastema may be predicted by
its localization in the planarian. An anterior blastema will regenerate a
head with the brain and the eyes, a posterior blastema will differentiate
into a posterior region. One exception may be mentioned. If two transverse cuts isolate a very small fragment of the anterior region, a
regenerated organism with two heads is obtained; the presumptive tail
blastema forms a head, too.
At what moment is the blastema determined?
What morphogenetic factors condition the differentiation of the
organs?
A. Determination of the Blastema
Abeloos (1930) showed that the regeneration buds of Planaria
(Dugesia) gonocephala are determined from the second or third day of
their formation. But the problem of how this determination is acquired
can be resolved only by withdrawing the blastema from the influence of
the organism. This was achieved by C. Sengel (1959b, 1960) working on
Dugesia lugubris. She cultivated in vitro 2-3 day old regeneration
blastemas. These blastemas, formed by the neoblasts, continued to
evolve. The head blastemas differentiated a head with a brain and eyes.
The tail blastemas became pigmented and differentiated only muscles.
TH. LENDER
retarded and often incomplete. The region of the body situated behind
the fundus of the pharynx is incapable of regenerating a head.
Stephan-Dubois and Kolmayer (1959) investigated the reason for this
deficiency. Methyl green-pyronine staining showed that neoblasts were
present in the pharyngeal and postpharyngeal region (Stephan-Dubois,
1961). The inability of the postpharyngeal region to regenerate the head,
therefore, was not attributable to the absence of neoblasts. If the prepharyngeal region was irradiated after decapitation, the neoblasts of the
region which could form a head blastema, were destroyed. But after a
certain time had elapsed, a head blastema did form by accumulation of
healthy neoblasts which had migrated from the postpharyngeal region
across the irradiated zone. The neoblasts of the postpharyngeal region
which were incapable of forming a head if the part anterior to the fundus
of the pharynx was removed, could do so if they were forced to move to
the anterior region. The inability of the postpharyngeal region to regenerate a head, then, was not due to the absence or different quality of
the neoblasts but, without doubt, to factors which inhibited their power
of regeneration in the postpharyngeal region itself (Kolmayer and
Stephan-Dubois, 1960).
III. Differentiation Factors
The later evolution of a regeneration blastema may be predicted by
its localization in the planarian. An anterior blastema will regenerate a
head with the brain and the eyes, a posterior blastema will differentiate
into a posterior region. One exception may be mentioned. If two transverse cuts isolate a very small fragment of the anterior region, a
regenerated organism with two heads is obtained; the presumptive tail
blastema forms a head, too.
At what moment is the blastema determined?
What morphogenetic factors condition the differentiation of the
organs?
A. Determination of the Blastema
Abeloos (1930) showed that the regeneration buds of Planaria
(Dugesia) gonocephala are determined from the second or third day of
their formation. But the problem of how this determination is acquired
can be resolved only by withdrawing the blastema from the influence of
the organism. This was achieved by C. Sengel (1959b, 1960) working on
Dugesia lugubris. She cultivated in vitro 2-3 day old regeneration
blastemas. These blastemas, formed by the neoblasts, continued to
evolve. The head blastemas differentiated a head with a brain and eyes.
The tail blastemas became pigmented and differentiated only muscles.