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PAUL BRIEN
young polyp by budding are set in motion solely by the older tissues, as
can be illustrated also in hydras in which the interstitial cells are prevented from gathering by irradiation with X-rays (Brien, 1953, 1954,
1956). The irradiated hydra stops feeding, deteriorates, and dies, growing
thin and dissociating. However, during the 10 days following the irradiation, the hydras are able to feed, to regenerate, and to bud. At this time
they form new polyps. The interstitial cells have no part in this. These
young polyps, it is true, being reconstituted exclusively by the epithelial
cells of the ectoderm and endoderm, are not viable. They have no nematocysts; they can neither feed nor grow (Fig. 12). The participation of
interstitial cells in indispensable only to perfect the definitive form of
the young polyp. Without them it remains incomplete and will soon die
(Brien and Reniers-Decoen, 1951).
In conclusion, blastogenesis does pertain to somatic cells. To show this,
and then to gain reproductive and ontogenic capacity, these cells must
undergo a cytological preparation just as germ cells do in the course of
gametogenesis in order to become ontogenic. These cells capable of blastogenesis are cells which have been engaged in somatic physiology, and
in this sense are differentiated. They are oriented histologically. At the
blastogenic area they dedifferentiate, and they return to a younger cytological condition, embryonic in nature. They then enlarge and acquire
basophilia by enrichment with ribonucleic acid. This dedifferentiation is
more or less deep, depending upon the composition of the elements which
are collaborating in the budding. It can be superficial and not modify
the original histological orientation which will be that followed in construction of the blastozooid. On the contrary, it can efface the primary
orientation and confer upon the cells which are undergoing this change a
new organogenic capacity, sometimes very extensive (dedifferentiation of
mesenchyme in Clavelina, of the epicardium in Polyclinidae, of the ectoderm in bryozoans).
This dedifferentiation poses very important cytological problems for
cellular life. Urbani and his collaborators have shown that dedifferentiation and redifferentiation in the blastema of regeneration in various
species of animals are accompanied by significant variations in proteolytic
enzyme activity. The organism sometimes makes use of cells called
"undifferentiated." Some cells are a component of differentiated tissues
to which they assure constant renewal; their fate is thus limited and
clearly oriented; these are the histoblasts. Other cells are scattered
through the organism and are polyvalent. Such are the archaeocytes of
sponges, the interstitial cells of hydras, the neoblasts of planarians. Not
PAUL BRIEN
young polyp by budding are set in motion solely by the older tissues, as
can be illustrated also in hydras in which the interstitial cells are prevented from gathering by irradiation with X-rays (Brien, 1953, 1954,
1956). The irradiated hydra stops feeding, deteriorates, and dies, growing
thin and dissociating. However, during the 10 days following the irradiation, the hydras are able to feed, to regenerate, and to bud. At this time
they form new polyps. The interstitial cells have no part in this. These
young polyps, it is true, being reconstituted exclusively by the epithelial
cells of the ectoderm and endoderm, are not viable. They have no nematocysts; they can neither feed nor grow (Fig. 12). The participation of
interstitial cells in indispensable only to perfect the definitive form of
the young polyp. Without them it remains incomplete and will soon die
(Brien and Reniers-Decoen, 1951).
In conclusion, blastogenesis does pertain to somatic cells. To show this,
and then to gain reproductive and ontogenic capacity, these cells must
undergo a cytological preparation just as germ cells do in the course of
gametogenesis in order to become ontogenic. These cells capable of blastogenesis are cells which have been engaged in somatic physiology, and
in this sense are differentiated. They are oriented histologically. At the
blastogenic area they dedifferentiate, and they return to a younger cytological condition, embryonic in nature. They then enlarge and acquire
basophilia by enrichment with ribonucleic acid. This dedifferentiation is
more or less deep, depending upon the composition of the elements which
are collaborating in the budding. It can be superficial and not modify
the original histological orientation which will be that followed in construction of the blastozooid. On the contrary, it can efface the primary
orientation and confer upon the cells which are undergoing this change a
new organogenic capacity, sometimes very extensive (dedifferentiation of
mesenchyme in Clavelina, of the epicardium in Polyclinidae, of the ectoderm in bryozoans).
This dedifferentiation poses very important cytological problems for
cellular life. Urbani and his collaborators have shown that dedifferentiation and redifferentiation in the blastema of regeneration in various
species of animals are accompanied by significant variations in proteolytic
enzyme activity. The organism sometimes makes use of cells called
"undifferentiated." Some cells are a component of differentiated tissues
to which they assure constant renewal; their fate is thus limited and
clearly oriented; these are the histoblasts. Other cells are scattered
through the organism and are polyvalent. Such are the archaeocytes of
sponges, the interstitial cells of hydras, the neoblasts of planarians. Not