THE EARLY EMBRYOGENESIS OF INSECTS
263
buted unevenly within an endoplasmic network, so that frequently one
may distinguish the more finely granular axial and marginal regions of
endoplasm from the interposed coarse yolk mantle. The endoplasm
is surrounded by ectoplasm. In 'yolk-rich' eggs this consists of the plasmalemma only, whereas in 'plasm-rich' eggs we find below the plasmalemma a yolk-free layer, the periplasmj ('Keimhautblastem'), which
in some cases may appear or increase during cleavage. Near the spot
where the oocyte nucleus dissolves there is always a cytoplasmic island
in which meiosis occurs. This 'maturation plasm' controls the meiotic
divisions and blocks mitosis (Counce, 1961) and soon afterwards disappears. Each cleavage nucleus is surrounded by a plasmic island;
nucleus and island together are referred to as a cleavage energid
(Krause, 1953). The energids are connected by the endoplasmic reticulum. All protoplasmic components may contain RNA (Jura et al., 1958,
1959). The distribution of these components differs in different species
(Counce, 1959; Ochiai, 1960; Seidler, 1940). Basophilic protein particles
or a compact oosome are frequently found near the posterior pole. The
typical cell organelles have been demonstrated by electron microscopy
to be present in the insect egg (Okada and Waddington, 1959; King,
1960), but their distribution in different egg regions and egg constituents
remains to be studied.
A. Egg Dimorphism
Sexual differences as demonstrated, for example, by chromosome
elimination in the Cecidomyidae (Geyer-Duszynska, 1959; Nicklas,
1959) are not usually visibly expressed in the ooplasm. In the scale
insect, Pseudaulacaspis pentagona, however, male eggs in which the
paternal set of chromosomes is eliminated are white and female eggs are
red. The latter are deposited first and the male eggs later on (Brown and
Bennett, 1957). Similarly, the mother's age may influence the sex of the
offspring in some Sternorrhynchi (Brown and DeLotto, 1959), whereas
in other cases the sex may be established during oogenesis by the quality
of food available to the mother (Buckle, 1959) or by the quantity
(Ulrich, 1936; Nikolai, 1961), or by the success or failure of egg infection
by symbionts (Büchner, 1954). Reduction, elimination, and cleavage
take different courses in the big male eggs and the small female eggs of
Oligarces even before the nutritive chambers, which differ in size, have
been absorbed (Hauschteck, 1959). According to Seidel and Reinhardt
(1959) and Reinhardt (1960), eggs for the drone honeybee differ in
architecture from those for the worker bee. Male eggs are longer and
bigger and contain less plasm; their endoplasmic gradients are weaker
f We should like to reserve the term 'cortex' for a layer of ectoplasm considered from a
physiological aspect.
263
buted unevenly within an endoplasmic network, so that frequently one
may distinguish the more finely granular axial and marginal regions of
endoplasm from the interposed coarse yolk mantle. The endoplasm
is surrounded by ectoplasm. In 'yolk-rich' eggs this consists of the plasmalemma only, whereas in 'plasm-rich' eggs we find below the plasmalemma a yolk-free layer, the periplasmj ('Keimhautblastem'), which
in some cases may appear or increase during cleavage. Near the spot
where the oocyte nucleus dissolves there is always a cytoplasmic island
in which meiosis occurs. This 'maturation plasm' controls the meiotic
divisions and blocks mitosis (Counce, 1961) and soon afterwards disappears. Each cleavage nucleus is surrounded by a plasmic island;
nucleus and island together are referred to as a cleavage energid
(Krause, 1953). The energids are connected by the endoplasmic reticulum. All protoplasmic components may contain RNA (Jura et al., 1958,
1959). The distribution of these components differs in different species
(Counce, 1959; Ochiai, 1960; Seidler, 1940). Basophilic protein particles
or a compact oosome are frequently found near the posterior pole. The
typical cell organelles have been demonstrated by electron microscopy
to be present in the insect egg (Okada and Waddington, 1959; King,
1960), but their distribution in different egg regions and egg constituents
remains to be studied.
A. Egg Dimorphism
Sexual differences as demonstrated, for example, by chromosome
elimination in the Cecidomyidae (Geyer-Duszynska, 1959; Nicklas,
1959) are not usually visibly expressed in the ooplasm. In the scale
insect, Pseudaulacaspis pentagona, however, male eggs in which the
paternal set of chromosomes is eliminated are white and female eggs are
red. The latter are deposited first and the male eggs later on (Brown and
Bennett, 1957). Similarly, the mother's age may influence the sex of the
offspring in some Sternorrhynchi (Brown and DeLotto, 1959), whereas
in other cases the sex may be established during oogenesis by the quality
of food available to the mother (Buckle, 1959) or by the quantity
(Ulrich, 1936; Nikolai, 1961), or by the success or failure of egg infection
by symbionts (Büchner, 1954). Reduction, elimination, and cleavage
take different courses in the big male eggs and the small female eggs of
Oligarces even before the nutritive chambers, which differ in size, have
been absorbed (Hauschteck, 1959). According to Seidel and Reinhardt
(1959) and Reinhardt (1960), eggs for the drone honeybee differ in
architecture from those for the worker bee. Male eggs are longer and
bigger and contain less plasm; their endoplasmic gradients are weaker
f We should like to reserve the term 'cortex' for a layer of ectoplasm considered from a
physiological aspect.