MORPHOGENESIS IN STENTOR
11
line zone. The primordium is correspondingly reversed: it now coils to
the animal's left during invagination and when the membranelles become functional their effective beating is now away from rather than
toward the mouthparts as is normally the case (Fig. 7). The adjacent
FIG. 7. Stentor of reversed asymmetry. Quarters of the cell were first transposed, by
rotating the anterior half through 180° on the posterior half and then by rotating the left
half through 180° on the right half. The normal stripe pattern is then reconstructed in
reverse. Location of mouthparts, contractile vacuole and nuclear chain and direction of
coiling of anläge are correspondingly reversed. Polarity of membranellar band, both
formed and in the primordium, is also reversed, with membranelles beating away from
the mouthparts. Repeated re-regeneration occurs, probably because mouthparts formed
are not perfect.
stripe pattern therefore seems somehow to be involved in the manner in
which the fine structures in the anläge are put together, reversed primordium sites producing reversed polarity in the membranellar band.
In turn, this polar reversal may result in structural disharmonies when
the end of the band coils and invaginates; for the mouthparts so produced are never complete mirror images of the normal and remain
defective, with the result that the specimen repeatedly re-regenerates
(as many as 12 times in succession) without ever forming satisfactory
ingestive structures (Tartar, 1960b).
B. Induction of Mouthparts Formation
Just as the axis of a developing amphibian embryo is said to be
regionalized, with one end developing the brain, so formation of mouthparts by inward coiling of the posterior end of the developing membranellar band may be said to be induced by the posterior pole of the
cell near which it normally lies. For if, by proper manipulation of the
stripe pattern, the formation of transverse primordia is caused (Tartar,
1956b), or when an early primordium is translocated to the frontal field
(Fig. 6b), the ends of these anlagen then He far away from the posterior
pole and they develop astomatously (Tartar, 1960a). Such demonstrations have been extended by Uhlig (1960), convincing him that there is
an inductive relationship between the posterior pole and mouthparts
formation.
If the transposition just mentioned is made later in development yet
11
line zone. The primordium is correspondingly reversed: it now coils to
the animal's left during invagination and when the membranelles become functional their effective beating is now away from rather than
toward the mouthparts as is normally the case (Fig. 7). The adjacent
FIG. 7. Stentor of reversed asymmetry. Quarters of the cell were first transposed, by
rotating the anterior half through 180° on the posterior half and then by rotating the left
half through 180° on the right half. The normal stripe pattern is then reconstructed in
reverse. Location of mouthparts, contractile vacuole and nuclear chain and direction of
coiling of anläge are correspondingly reversed. Polarity of membranellar band, both
formed and in the primordium, is also reversed, with membranelles beating away from
the mouthparts. Repeated re-regeneration occurs, probably because mouthparts formed
are not perfect.
stripe pattern therefore seems somehow to be involved in the manner in
which the fine structures in the anläge are put together, reversed primordium sites producing reversed polarity in the membranellar band.
In turn, this polar reversal may result in structural disharmonies when
the end of the band coils and invaginates; for the mouthparts so produced are never complete mirror images of the normal and remain
defective, with the result that the specimen repeatedly re-regenerates
(as many as 12 times in succession) without ever forming satisfactory
ingestive structures (Tartar, 1960b).
B. Induction of Mouthparts Formation
Just as the axis of a developing amphibian embryo is said to be
regionalized, with one end developing the brain, so formation of mouthparts by inward coiling of the posterior end of the developing membranellar band may be said to be induced by the posterior pole of the
cell near which it normally lies. For if, by proper manipulation of the
stripe pattern, the formation of transverse primordia is caused (Tartar,
1956b), or when an early primordium is translocated to the frontal field
(Fig. 6b), the ends of these anlagen then He far away from the posterior
pole and they develop astomatously (Tartar, 1960a). Such demonstrations have been extended by Uhlig (1960), convincing him that there is
an inductive relationship between the posterior pole and mouthparts
formation.
If the transposition just mentioned is made later in development yet