286
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
mous aggregation of reticuloplasm is one factor and mitotic movement
of nuclei is a second factor. A third is R. Hertwig's nucleoplasmic ratio,
as inferred from the fact that big nuclei are endowed with big plasma
islands (e.g. Gryllus; Mahr, 1960a: Apis; Reinhardt, 1960). Cooperation
of these factors effects the typical synchronous phase of cleavage during
which the energids are distributed dichotomously throughout the endoplasmic space around the CC.
C. Nucleocytoplasmic Interactions
In early stages of development we may expect maturation, fertilization, nucleation of posterior pole region or oosome, nucleation of
periplasm, and change from sychronous to heterochronous mitoses to be
critical stages for reactions between plasm and nuclei in the insect egg.
Subsequent nucleocytoplasmic interactions take place in blastemas and
therefore are not to be considered here.
The stage from which onward nuclear factors are indispensable for
development can be inferred from the type and time of termination of
the autonomous ooplasmic processes mentioned above. Pseudo-cleavage
in Gryllus produces about 512 plasma islands situated in the axial and
marginal plasms and looking like primary and secondary vitellophags
('pseudo-vitellophags', Figs. 28-9 of Mahr, 1960). Beyond this, no
development takes place. In contrast, even without an activation centre,
an egg may form blastoderm cells and cleave the yolk (Fig. 7f-h).
Blastoderm formation accordingly depends upon some nuclear reaction;
by themselves, the plasma islands will not merge with the periplasm
although they may touch it. Other insects may, without nuclei, form a
spheroid of plasma islands and even a non-nucleated blastoderm (e.g.
Apis; Reinhardt, 1960), but aggregation of secondary periplasm is lacking. Accordingly, production of this periplasm must be due to nuclear
influences, most probably from the highly differentiated nuclei of
primary vitellophags which in these insects degenerate soon afterwards.
In Habrobracon, on the other hand, there is no spheroid formation
and no centrifugal migration of plasma islands with 'empty' nuclei
(von Borstel, 1955; cf. Section V B). The 128-nuclei stage, therefore,
during which the energids should approach the posterior pole and
surface, appears to be critical in Habrobracon for the onset of gene
function in development. Drosophila embryos, homozygous for certain
genes, cease to develop after the Vlth cleavage division (cf. Counce,
1961). Presence of cleavage nuclei is thought to be sufficient to activate
the AC of Platycnemis (Seidel, 1932); this activation, however, might
equally be due to plasmic factors carried by the energid and possibly
originating from the cleavage centre.
The influence of the ooplasm upon the nuclei, although without doubt
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
mous aggregation of reticuloplasm is one factor and mitotic movement
of nuclei is a second factor. A third is R. Hertwig's nucleoplasmic ratio,
as inferred from the fact that big nuclei are endowed with big plasma
islands (e.g. Gryllus; Mahr, 1960a: Apis; Reinhardt, 1960). Cooperation
of these factors effects the typical synchronous phase of cleavage during
which the energids are distributed dichotomously throughout the endoplasmic space around the CC.
C. Nucleocytoplasmic Interactions
In early stages of development we may expect maturation, fertilization, nucleation of posterior pole region or oosome, nucleation of
periplasm, and change from sychronous to heterochronous mitoses to be
critical stages for reactions between plasm and nuclei in the insect egg.
Subsequent nucleocytoplasmic interactions take place in blastemas and
therefore are not to be considered here.
The stage from which onward nuclear factors are indispensable for
development can be inferred from the type and time of termination of
the autonomous ooplasmic processes mentioned above. Pseudo-cleavage
in Gryllus produces about 512 plasma islands situated in the axial and
marginal plasms and looking like primary and secondary vitellophags
('pseudo-vitellophags', Figs. 28-9 of Mahr, 1960). Beyond this, no
development takes place. In contrast, even without an activation centre,
an egg may form blastoderm cells and cleave the yolk (Fig. 7f-h).
Blastoderm formation accordingly depends upon some nuclear reaction;
by themselves, the plasma islands will not merge with the periplasm
although they may touch it. Other insects may, without nuclei, form a
spheroid of plasma islands and even a non-nucleated blastoderm (e.g.
Apis; Reinhardt, 1960), but aggregation of secondary periplasm is lacking. Accordingly, production of this periplasm must be due to nuclear
influences, most probably from the highly differentiated nuclei of
primary vitellophags which in these insects degenerate soon afterwards.
In Habrobracon, on the other hand, there is no spheroid formation
and no centrifugal migration of plasma islands with 'empty' nuclei
(von Borstel, 1955; cf. Section V B). The 128-nuclei stage, therefore,
during which the energids should approach the posterior pole and
surface, appears to be critical in Habrobracon for the onset of gene
function in development. Drosophila embryos, homozygous for certain
genes, cease to develop after the Vlth cleavage division (cf. Counce,
1961). Presence of cleavage nuclei is thought to be sufficient to activate
the AC of Platycnemis (Seidel, 1932); this activation, however, might
equally be due to plasmic factors carried by the energid and possibly
originating from the cleavage centre.
The influence of the ooplasm upon the nuclei, although without doubt