M O R P H O G E N E S I S I N S T E N T O R
5
tained, in which original anterior and posterior polar regions are now
adjacent, then the striping is cut across at the bend by a fission line, and
the cut ends are gathered together as a new posterior pole where a holdfast develops. This process is therefore like that by which a new 'tail'
FIG. 2. Unusual manner of tail-pole formation in folded longitudinal halves, (a) Halfcell folds on itself to cover wound surface, bringing head and tail poles together, (b)
Striping cut by fission line along the bend, (c) Gathering of cut ends to form new tail pole.
(d) New pole formed, old tail pole regresses and feeding organelles in process of regenerating. (e) Commoner occurrence, in which original polarization is preserved and head and
tail poles separate by growth between them of new striping (x). (After Tartar, 1956b.)
is produced for the anterior daughter in division, except that the striping of the posterior half also participates, regardless of the fact that its
original polarity is 'incorrect' for this formation. However, this is not
the only way of resolving the morphological dilemma. Usually new
stripes grow between the head and tail remnants which are therefore
moved apart until they become polar opposites again (Fig. 2e).
Lateral striping can be slashed through repeatedly and indiscriminately without provoking the formation of an oral regeneration primordium. Cut edges of the ectoplasm simply come together and heal, and
the ciliary rows and pigment bands realign and join. Feeding organelles
can also be cut through the region of the mouthparts or the membranellar
band and they simply heal together; but if the parts are far displaced so
they cannot join, or if all or any portion is entirely removed, then a new
set is regenerated through primordium formation which largely replaces
the old, though an aboral portion of the old membranelies, if present,
may remain intact and join with the new. The more of the original feeding organelles left intact, the more delayed the regeneration. This indicates that all portions of these organelles participate in an inhibition of
primordium formation; yet the inhibition is apparently not a simple
chemical one since, when cut and displaced, all parts of the feeding
organelles are present yet regeneration eventually occurs because the
parts are no longer joined in their proper relationships.
Calkins' (1933) distinction between basic and derived parts of the
protozoan cell may be useful in the present connection. The lateral
striping with its ciliary rows or kineties is apparently basic, i.e. never
regenerating de novo, passed on by direct inheritance to daughter cells,
5
tained, in which original anterior and posterior polar regions are now
adjacent, then the striping is cut across at the bend by a fission line, and
the cut ends are gathered together as a new posterior pole where a holdfast develops. This process is therefore like that by which a new 'tail'
FIG. 2. Unusual manner of tail-pole formation in folded longitudinal halves, (a) Halfcell folds on itself to cover wound surface, bringing head and tail poles together, (b)
Striping cut by fission line along the bend, (c) Gathering of cut ends to form new tail pole.
(d) New pole formed, old tail pole regresses and feeding organelles in process of regenerating. (e) Commoner occurrence, in which original polarization is preserved and head and
tail poles separate by growth between them of new striping (x). (After Tartar, 1956b.)
is produced for the anterior daughter in division, except that the striping of the posterior half also participates, regardless of the fact that its
original polarity is 'incorrect' for this formation. However, this is not
the only way of resolving the morphological dilemma. Usually new
stripes grow between the head and tail remnants which are therefore
moved apart until they become polar opposites again (Fig. 2e).
Lateral striping can be slashed through repeatedly and indiscriminately without provoking the formation of an oral regeneration primordium. Cut edges of the ectoplasm simply come together and heal, and
the ciliary rows and pigment bands realign and join. Feeding organelles
can also be cut through the region of the mouthparts or the membranellar
band and they simply heal together; but if the parts are far displaced so
they cannot join, or if all or any portion is entirely removed, then a new
set is regenerated through primordium formation which largely replaces
the old, though an aboral portion of the old membranelies, if present,
may remain intact and join with the new. The more of the original feeding organelles left intact, the more delayed the regeneration. This indicates that all portions of these organelles participate in an inhibition of
primordium formation; yet the inhibition is apparently not a simple
chemical one since, when cut and displaced, all parts of the feeding
organelles are present yet regeneration eventually occurs because the
parts are no longer joined in their proper relationships.
Calkins' (1933) distinction between basic and derived parts of the
protozoan cell may be useful in the present connection. The lateral
striping with its ciliary rows or kineties is apparently basic, i.e. never
regenerating de novo, passed on by direct inheritance to daughter cells,