12
VANCE T A R T A R
before any inward coiling has begun, the primordium forms good
mouthparts even at the anterior end. The anläge therefore undergoes
progressive determination of its fate with the passage of time, just as in
embryogenesis. We can conclude that after the posterior pole has already
exerted its influence, the primordium is then quite capable of bringing
its development to completion regardless of its surroundings. The same
can be shown in deletion experiments (Tartar, 1957c). Excision of sections of the early primordium are always compensated and normal development ensues. Later, removal of the anterior half results in too
short a membranellar band; excising the posterior half or the prospective oral region produces development without a mouth; and it is even
the case that if a small piece of the primordium is removed in the region
of the prospective buccal pouch a set of feeding organelles is then produced, complete in every respect except that this pouch is missing.
V. Activation and Inhibition of
Primordium Formation in Development
Oral primordium formation is elicited whenever all or part of the feeding organelles is excised. If two stentors are grafted in parabiosis and
the mouthparts are excised from one, primordia appear in both animals,
the one on the cut side serving for regeneration while the other produces
reorganizational replacement of the intact organelles. Apparently the
stimulus for regeneration passes from one cell to the other and this is
independent of the relative size of the partners (Tartar, 1954). Weisz
(1956) found that if a Stentor already in regeneration is grafted to a
morphostatic animal (normal feeding animal, not regenerating, reorganizing, or dividing), the latter is forced to produce a primordium
and undergo reorganization; but this occurs only when the affected
partner is a smaller cell (Fig. 8a). If the morphostatic partner is the
same size or larger the influence moves in the opposite direction, the
regeneration primordium being then resorbed (Fig. 8b) (Tartar, 1958).
Morphostasis evidently involves a cell state or condition of inhibition
so strong that this influence can even pass to an adjoining cell and cause
the resorption of a primordium already well formed. Conversely, primordium formation seems to be accompanied by a cell state or condition sufficient not only to support primordium formation and development but also to compel the same in a smaller cell adjoined. Since the
relative size of the two cells in parabiosis determines the direction of
influence and the resulting performance, it is suggested that the whole
cell in some pervasive aspect is involved in these cell states. The larger
the Stentor the greater its influence on its partner.
Lag effects are often observable in the mutual influence of the two
VANCE T A R T A R
before any inward coiling has begun, the primordium forms good
mouthparts even at the anterior end. The anläge therefore undergoes
progressive determination of its fate with the passage of time, just as in
embryogenesis. We can conclude that after the posterior pole has already
exerted its influence, the primordium is then quite capable of bringing
its development to completion regardless of its surroundings. The same
can be shown in deletion experiments (Tartar, 1957c). Excision of sections of the early primordium are always compensated and normal development ensues. Later, removal of the anterior half results in too
short a membranellar band; excising the posterior half or the prospective oral region produces development without a mouth; and it is even
the case that if a small piece of the primordium is removed in the region
of the prospective buccal pouch a set of feeding organelles is then produced, complete in every respect except that this pouch is missing.
V. Activation and Inhibition of
Primordium Formation in Development
Oral primordium formation is elicited whenever all or part of the feeding organelles is excised. If two stentors are grafted in parabiosis and
the mouthparts are excised from one, primordia appear in both animals,
the one on the cut side serving for regeneration while the other produces
reorganizational replacement of the intact organelles. Apparently the
stimulus for regeneration passes from one cell to the other and this is
independent of the relative size of the partners (Tartar, 1954). Weisz
(1956) found that if a Stentor already in regeneration is grafted to a
morphostatic animal (normal feeding animal, not regenerating, reorganizing, or dividing), the latter is forced to produce a primordium
and undergo reorganization; but this occurs only when the affected
partner is a smaller cell (Fig. 8a). If the morphostatic partner is the
same size or larger the influence moves in the opposite direction, the
regeneration primordium being then resorbed (Fig. 8b) (Tartar, 1958).
Morphostasis evidently involves a cell state or condition of inhibition
so strong that this influence can even pass to an adjoining cell and cause
the resorption of a primordium already well formed. Conversely, primordium formation seems to be accompanied by a cell state or condition sufficient not only to support primordium formation and development but also to compel the same in a smaller cell adjoined. Since the
relative size of the two cells in parabiosis determines the direction of
influence and the resulting performance, it is suggested that the whole
cell in some pervasive aspect is involved in these cell states. The larger
the Stentor the greater its influence on its partner.
Lag effects are often observable in the mutual influence of the two