20
VANCE TARTAR
stops and early primordia are even resorbed in enucleates. At what has
been called stage 5, however, when the membranellar band is already
complete though there is no indication yet of forming mouthparts, full
development after enucleation is realized. This indicates that nucleardependent synthesis of parts is then almost if not entirely finished, and
that invagination of the membranellar band and incorporation of adjacent ectoplasm to form the gullet lining and buccal pouch, as well as
migration of the feeding organelles to their definitive location, can occur
in the absence of the macronucleus. In cell division, formation and constriction of the fission furrow does not require the presence of the nucleus
(de Terra, 1960; Tartar, 1960a), reminding one of the cleavage capacities
of enucleated eggs (Harvey, 1936). All the evidence in Protozoa indicates that the nucleus is essential for synthesis, that the nucleus supports this function by the emission of certain substances, probably
enzymes or their precursors, and that these substances are short lived
in the cytoplasm.
C. Nuclear Behaviour Governed by the Cytoplasm
Besides performing essential functions, the macronucleus of Stentor
has a specific behaviour as an organelle in itself. Even when displaced,
the macronuclear chain always returns to a definite location in the cell,
subcortical in position and distributed as shown in Fig. la. Though the
point has not yet been conclusively demonstrated, all indications are that
the stripe pattern determines the location of the nucleus. For instance, if
the stripe pattern becomes reversed the location of the macronuclear
chain is also reversed (see Fig. 7).
During regeneration and reorganization, and most emphatically during cell division, the nodes of the macronucleus coalesce into one compact mass. After primordium development this mass elongates and
becomes sausage-shaped, and then, divided or not, renodulates as a
chain of beads. All aspects of this behaviour seem to be controlled by the
cytoplasm. Weisz (1956) found that dividing stentors with clumping
macronucleus induced coalescence in nuclei of morphostatic parabiotic
partners; and de Terra (1960) demonstrated that an implanted extra
fusion nucleus extends and renodulates along with that of a host divider
but not in a morphostatic cell. If the clumped nucleus within a reorganizing Stentor is greatly disturbed by teasing with a glass needle it
may be prevented from renodulating after primordium development, in
which case it remains sausage-shaped indefinitely or until the specimen
forms a new oral primordium, whereupon the nucleus condenses and
renodulates in correlation with the developing anläge (Tartar, 1960a).
The macronucleus seems incapable of independent fission, for de Terra
(1960) found that when the location of a dividing nucleus is shifted in
VANCE TARTAR
stops and early primordia are even resorbed in enucleates. At what has
been called stage 5, however, when the membranellar band is already
complete though there is no indication yet of forming mouthparts, full
development after enucleation is realized. This indicates that nucleardependent synthesis of parts is then almost if not entirely finished, and
that invagination of the membranellar band and incorporation of adjacent ectoplasm to form the gullet lining and buccal pouch, as well as
migration of the feeding organelles to their definitive location, can occur
in the absence of the macronucleus. In cell division, formation and constriction of the fission furrow does not require the presence of the nucleus
(de Terra, 1960; Tartar, 1960a), reminding one of the cleavage capacities
of enucleated eggs (Harvey, 1936). All the evidence in Protozoa indicates that the nucleus is essential for synthesis, that the nucleus supports this function by the emission of certain substances, probably
enzymes or their precursors, and that these substances are short lived
in the cytoplasm.
C. Nuclear Behaviour Governed by the Cytoplasm
Besides performing essential functions, the macronucleus of Stentor
has a specific behaviour as an organelle in itself. Even when displaced,
the macronuclear chain always returns to a definite location in the cell,
subcortical in position and distributed as shown in Fig. la. Though the
point has not yet been conclusively demonstrated, all indications are that
the stripe pattern determines the location of the nucleus. For instance, if
the stripe pattern becomes reversed the location of the macronuclear
chain is also reversed (see Fig. 7).
During regeneration and reorganization, and most emphatically during cell division, the nodes of the macronucleus coalesce into one compact mass. After primordium development this mass elongates and
becomes sausage-shaped, and then, divided or not, renodulates as a
chain of beads. All aspects of this behaviour seem to be controlled by the
cytoplasm. Weisz (1956) found that dividing stentors with clumping
macronucleus induced coalescence in nuclei of morphostatic parabiotic
partners; and de Terra (1960) demonstrated that an implanted extra
fusion nucleus extends and renodulates along with that of a host divider
but not in a morphostatic cell. If the clumped nucleus within a reorganizing Stentor is greatly disturbed by teasing with a glass needle it
may be prevented from renodulating after primordium development, in
which case it remains sausage-shaped indefinitely or until the specimen
forms a new oral primordium, whereupon the nucleus condenses and
renodulates in correlation with the developing anläge (Tartar, 1960a).
The macronucleus seems incapable of independent fission, for de Terra
(1960) found that when the location of a dividing nucleus is shifted in