MORPHOGENESIS IN STENTOR
3
gullet, and cytostome. The contractile vacuole is invariably found to the
left of the gullet and an anal pore lies nearby. The macronucleus is a
string of nodes lying underneath the ectoplasm and is located with great
regularity as shown in the sketch (Fig. la). Numerous micronuclei lie
along the macronuclear chain but they are entirely dispensable for all
cell functions except conjugation (Schwartz, 1935). For brevity we can
simply refer to the macronucleus as the nucleus, mindful that it originates in conjugation from chromosomal micronuclei.
Electron microscopy has revealed an extraordinary fine structure in
the parts enumerated. For example, in the related 8. polymorphous each
of the 250 membranelies consists of three rows of from 20 to 25 cilia,
each cilium arising from a kinetosome which also gives off a fibre to the
interior, all these ciliary rootlets being neatly packed together to form a
fan terminating in a stalk which is connected with the stalks of adjacent
membranelles (Randall and Jackson, 1958). Like other highly complex
ciliates and flagellates, Stentor is notable for the variety and number
of organelles within a single cell.
B. Origin of Two Stentors from One in Division
Stentors reproduce by converting one form and individuality into
two which are then separated by cell division (Fig. Ib-d). The original
feeding organelles and contractile vacuole pass to the anterior daughter,
the tail pole and holdfast remaining as part of the posterior offspring.
This direct inheritance makes for a certain disproportion in the progeny
which is soon adjusted by subtle changes (Morgan, 1901; Weisz, 1951).
The posterior daughter acquires a new contractile vacuole and set of
feeding organelles. As the oral primordium develops it cuts off an area
of lateral striping which is carried forward as the new broad end or
frontal field of the posterior daughter, and most of this striping is newly
developed within the curvature of the anläge. For the anterior daughter
a new tail pole is produced by constriction of the division furrow which,
in proceeding forward around the primordium, cuts out a section of
lateral stripes so that when the anterior stripes come together they form
a herringbone pattern contributing to the conical shape. The cortical
structure which forms the lateral striping is therefore simply cut across
by the fission line and divided between the two daughters. During this
process the beads of the macronucleus coalesce into a ball which then
extends into a sausage-shaped organ and is cut in two by the cell constriction, the separate parts renodulating, each to about the original
number of nuclear beads.
Sub-cortically, granular carbohydrate reserves located toward the
posterior end of the cell are also divided equally between the two
daughters (Weisz, 1949a). Half the granules stream forward and the
3
gullet, and cytostome. The contractile vacuole is invariably found to the
left of the gullet and an anal pore lies nearby. The macronucleus is a
string of nodes lying underneath the ectoplasm and is located with great
regularity as shown in the sketch (Fig. la). Numerous micronuclei lie
along the macronuclear chain but they are entirely dispensable for all
cell functions except conjugation (Schwartz, 1935). For brevity we can
simply refer to the macronucleus as the nucleus, mindful that it originates in conjugation from chromosomal micronuclei.
Electron microscopy has revealed an extraordinary fine structure in
the parts enumerated. For example, in the related 8. polymorphous each
of the 250 membranelies consists of three rows of from 20 to 25 cilia,
each cilium arising from a kinetosome which also gives off a fibre to the
interior, all these ciliary rootlets being neatly packed together to form a
fan terminating in a stalk which is connected with the stalks of adjacent
membranelles (Randall and Jackson, 1958). Like other highly complex
ciliates and flagellates, Stentor is notable for the variety and number
of organelles within a single cell.
B. Origin of Two Stentors from One in Division
Stentors reproduce by converting one form and individuality into
two which are then separated by cell division (Fig. Ib-d). The original
feeding organelles and contractile vacuole pass to the anterior daughter,
the tail pole and holdfast remaining as part of the posterior offspring.
This direct inheritance makes for a certain disproportion in the progeny
which is soon adjusted by subtle changes (Morgan, 1901; Weisz, 1951).
The posterior daughter acquires a new contractile vacuole and set of
feeding organelles. As the oral primordium develops it cuts off an area
of lateral striping which is carried forward as the new broad end or
frontal field of the posterior daughter, and most of this striping is newly
developed within the curvature of the anläge. For the anterior daughter
a new tail pole is produced by constriction of the division furrow which,
in proceeding forward around the primordium, cuts out a section of
lateral stripes so that when the anterior stripes come together they form
a herringbone pattern contributing to the conical shape. The cortical
structure which forms the lateral striping is therefore simply cut across
by the fission line and divided between the two daughters. During this
process the beads of the macronucleus coalesce into a ball which then
extends into a sausage-shaped organ and is cut in two by the cell constriction, the separate parts renodulating, each to about the original
number of nuclear beads.
Sub-cortically, granular carbohydrate reserves located toward the
posterior end of the cell are also divided equally between the two
daughters (Weisz, 1949a). Half the granules stream forward and the