276
G E R H A R D K R A U S E A N D K L A U S S A N D E R
If situated near the middle of the egg (e.g. Gryllus, T achy eines) the
CC remains the central point of energid distribution (Krause, 1938a).
In other cases, the energids display a preference for certain directions;
they may migrate anteriorly near the egg surface (e.g., Locusta; Roonwal,
1936), or move backwards spreading either dichotomously (e.g. Pyrilla;
Sander, 1956) or along the central axis (e.g. Apis, Pig. 3b). In Notonecta
(Fig. 4c x ) after the IVth cleavage division, those energids which have
reached the middle of the egg orientate their spindles parallel to the
longitudinal egg axis and thereby effect further backward migration. As
in Apis (Fig. 3a, b) and Calliphora (Nitschmann, 1961), the swarm of
energids in other insects may move backwards en bloc within the axial
endoplasm. Only these movements in internal egg regions may be under
control from the CC; new controlling factors are likely to be responsible
for spheroid formation, especially since the spindles of spheroid energids
orientate only tangentially after about the Vlth cleavage division. The
energids constituting the spheroid are situated superficially in Gryllus,
Platycnemis and other hemimetabolous forms, whereas in holometabolous insects the spheroid is usually situated internally and its shape does
not quite correspond to that of the egg itself. The eccentric distribution
of ooplasm in Plodia (Müller, 1938) and Ephestia (Sehl, 1931) is reflected
by the energid spheroid which forms in the anterior region and expands
backwards, whereas the reverse situation is found in Tenebrio (Ewest,
1937). In the diploid egg of the honey-bee, the nuclei migrate as a
swarm in the axial plasm and then form a club-shaped spheroid near the
DC (Fig. 3b). In the haploid egg, this club-shaped arrangement is not so
obvious; there the energids invade the whole egg space as a swarm
originating from the CC. Thus, the DC may have greater influence in the
marginal endoplasm of the worker egg.
Formation and migration of a swarm of energids together with subsequent spheroid formation are especially well shown by the egg of
Panorpa (Fig. 4b; Ando, 1960; Wolf, unpublished). During cleavage
divisions I-IV, nuclei within a common plasma island migrate from the
original site of the zygote nucleus (85% level) into the region of the presumptive germ anläge (25% level). There the behaviour of the nuclei
changes. They acquire separate plasma islands and arrange themselves in
the shape of a spheroid which during cleavage divisions V I I - I X spreads
mainly forward so as to become adapted to the shape of the egg. The
periplasm is reached first at the equator and not near the posterior pole
as might be expected. The ooplasmic conditions in Panorpa controlling
these changes in preferential direction of migrating energids are not yet
known.
These few examples of energid movements stress the necessity of
recognizing different controlling gradients and centres in the ooplasm.
G E R H A R D K R A U S E A N D K L A U S S A N D E R
If situated near the middle of the egg (e.g. Gryllus, T achy eines) the
CC remains the central point of energid distribution (Krause, 1938a).
In other cases, the energids display a preference for certain directions;
they may migrate anteriorly near the egg surface (e.g., Locusta; Roonwal,
1936), or move backwards spreading either dichotomously (e.g. Pyrilla;
Sander, 1956) or along the central axis (e.g. Apis, Pig. 3b). In Notonecta
(Fig. 4c x ) after the IVth cleavage division, those energids which have
reached the middle of the egg orientate their spindles parallel to the
longitudinal egg axis and thereby effect further backward migration. As
in Apis (Fig. 3a, b) and Calliphora (Nitschmann, 1961), the swarm of
energids in other insects may move backwards en bloc within the axial
endoplasm. Only these movements in internal egg regions may be under
control from the CC; new controlling factors are likely to be responsible
for spheroid formation, especially since the spindles of spheroid energids
orientate only tangentially after about the Vlth cleavage division. The
energids constituting the spheroid are situated superficially in Gryllus,
Platycnemis and other hemimetabolous forms, whereas in holometabolous insects the spheroid is usually situated internally and its shape does
not quite correspond to that of the egg itself. The eccentric distribution
of ooplasm in Plodia (Müller, 1938) and Ephestia (Sehl, 1931) is reflected
by the energid spheroid which forms in the anterior region and expands
backwards, whereas the reverse situation is found in Tenebrio (Ewest,
1937). In the diploid egg of the honey-bee, the nuclei migrate as a
swarm in the axial plasm and then form a club-shaped spheroid near the
DC (Fig. 3b). In the haploid egg, this club-shaped arrangement is not so
obvious; there the energids invade the whole egg space as a swarm
originating from the CC. Thus, the DC may have greater influence in the
marginal endoplasm of the worker egg.
Formation and migration of a swarm of energids together with subsequent spheroid formation are especially well shown by the egg of
Panorpa (Fig. 4b; Ando, 1960; Wolf, unpublished). During cleavage
divisions I-IV, nuclei within a common plasma island migrate from the
original site of the zygote nucleus (85% level) into the region of the presumptive germ anläge (25% level). There the behaviour of the nuclei
changes. They acquire separate plasma islands and arrange themselves in
the shape of a spheroid which during cleavage divisions V I I - I X spreads
mainly forward so as to become adapted to the shape of the egg. The
periplasm is reached first at the equator and not near the posterior pole
as might be expected. The ooplasmic conditions in Panorpa controlling
these changes in preferential direction of migrating energids are not yet
known.
These few examples of energid movements stress the necessity of
recognizing different controlling gradients and centres in the ooplasm.