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G E R H A R D K R A U S E AND K L A U S S A N D E R
the whole mesoderm (k, o). Cephalic and abdominal differentiation
centres correspond in position to the cleavage centre and a hypothetical
activation centre, respectively. The yolk plasmodium may not be an
autonomous dynamic system since these initial regions cannot be shifted
by regulation. Therefore dynamic and topical prerequisites for differentiation centres must be contained in the blastoderm.
Ligation experiments show a certain interdependence of egg regions.
Following ligature during the dorsal fold stage, posterior isolates do not
develop further unless they contain the V l l t h abdominal segment situated in front of the posterior border fold (BF). After early isolation,
even bigger posterior egg parts furnished with nuclei are not capable of
differentiation (p). Anterior egg parts isolated during the head fold stage
continue to develop only if they include the anterior border fold. Therefore, topical prerequisites for cephalic and abdominal DC are to be expected in the region between the border folds. In contrast to eggs divided
during late blastoderm stages (r), eggs ligatured up to the early blastoderm lack some segments even if both fragments continue development
(p, q, s); in this case, the material located near the ligature is used to
form segments normally located closer to the poles. The disappearance
of segments cannot be due solely to transformation of their blastodermal
anlagen into supernumerary vitellophags since, besides a considerable
discrepancy between bulk of lost segments and number of supernumerary vitellophags, segments may also be suppressed if ligature is carried
out before blastoderm formation.
All these results, while certainly not corroborating the idea of strict
mosaicism, might be due to interference with an ooplasmic anteriorposterior reaction system as inferred by Sander (1960) from comparable
results in Euscelis (see Section VII B). This system controlling metameric organization might equally be correlated with the activation and
cleavage centres. Yet the question remains open as to whether this
system in Calliphora is not augmented by some sort of metameric prerequisites in the periplasm, i.e., by a displaceable series of topical factors
which predispose the development of certain segments. At any rate, the
egg of Calliphora does not conform to the mosaic type; it rather contains
the same ooplasmic reaction systems as do insect eggs with well developed blastokinesis, but modified into a rather rigid plasma-rich construction with reaction partners situated in loco so as to ensure rapid
development.
B. Antagonistic Polar Prerequisites
The egg of the leaf hopper, Euscelis, strikingly illustrates the fact that
the formation of defective embryos, following operation even during the
earliest stages, is not a proof of mosaicism. These defects are due rather
G E R H A R D K R A U S E AND K L A U S S A N D E R
the whole mesoderm (k, o). Cephalic and abdominal differentiation
centres correspond in position to the cleavage centre and a hypothetical
activation centre, respectively. The yolk plasmodium may not be an
autonomous dynamic system since these initial regions cannot be shifted
by regulation. Therefore dynamic and topical prerequisites for differentiation centres must be contained in the blastoderm.
Ligation experiments show a certain interdependence of egg regions.
Following ligature during the dorsal fold stage, posterior isolates do not
develop further unless they contain the V l l t h abdominal segment situated in front of the posterior border fold (BF). After early isolation,
even bigger posterior egg parts furnished with nuclei are not capable of
differentiation (p). Anterior egg parts isolated during the head fold stage
continue to develop only if they include the anterior border fold. Therefore, topical prerequisites for cephalic and abdominal DC are to be expected in the region between the border folds. In contrast to eggs divided
during late blastoderm stages (r), eggs ligatured up to the early blastoderm lack some segments even if both fragments continue development
(p, q, s); in this case, the material located near the ligature is used to
form segments normally located closer to the poles. The disappearance
of segments cannot be due solely to transformation of their blastodermal
anlagen into supernumerary vitellophags since, besides a considerable
discrepancy between bulk of lost segments and number of supernumerary vitellophags, segments may also be suppressed if ligature is carried
out before blastoderm formation.
All these results, while certainly not corroborating the idea of strict
mosaicism, might be due to interference with an ooplasmic anteriorposterior reaction system as inferred by Sander (1960) from comparable
results in Euscelis (see Section VII B). This system controlling metameric organization might equally be correlated with the activation and
cleavage centres. Yet the question remains open as to whether this
system in Calliphora is not augmented by some sort of metameric prerequisites in the periplasm, i.e., by a displaceable series of topical factors
which predispose the development of certain segments. At any rate, the
egg of Calliphora does not conform to the mosaic type; it rather contains
the same ooplasmic reaction systems as do insect eggs with well developed blastokinesis, but modified into a rather rigid plasma-rich construction with reaction partners situated in loco so as to ensure rapid
development.
B. Antagonistic Polar Prerequisites
The egg of the leaf hopper, Euscelis, strikingly illustrates the fact that
the formation of defective embryos, following operation even during the
earliest stages, is not a proof of mosaicism. These defects are due rather