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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
posterior cell movements leading to germ anläge formation and anatropsis (Fig. 6d-f, curve IV); the cause for these morphogenetic movements
must therefore lie in the yolk plasmodium.
A factor region near the posterior pole has been demonstrated in
other insects as well (e.g. Camponotus; Reith, 1931, 1932,: Tenebrio;
Ewest, 1937) and in some cases (Tachycines, Notonecta; Krause, 1938b:
Euscelis; Sander, 1959) is thought to be homologous to the AC of Pia -
tycnemis. Mahr (1960b) demonstrated that the position of the AC differs
slightly in different egg clusters of Gryllus. By a refined technique of
ligation, he was able to demonstrate also a slight spread of effects of the
centre between the 2- and 512-nuclei stage. Removal of the AC in Gryllus
is followed by extraembryonic development (Fig. 7f-h) as in Platyznemis. The egg of Tenebrio passes a critical period during cleavages VI
and VII (Ewest, 1937). Posterior pole cautery before the 64-nuclei stage
even prevents formation of the energid spheroid and of the blastoderm;
those energids which have not become inactivated by heat become primary vitellophags in the interior part of the egg, whereas in the dense
marginal plasm of the prospective germ disc, plasma islands appear with
a distribution similar to that of secondary vitellophags in normal development. The suppression of spheroid and blastoderm formation may be
ascribed to destruction of an AC not yet functioning; however, it may
equally well be due to a toxic substance created by early cautery. Operation after the 64-nuclei stage is followed by formation of an energid
spheroid, blastoderm, primary and secondary vitellophags, yolk cleavage, and even yolk contraction, but no germ anläge appears. From
this, one might conclude that an AC has become effective after the 64nuclei stage, but some differentiation factor necessary for germ anläge
formation and even for predisposition of the germ anläge in the energid
spheroid (normally the energids accumulate in the embryonic egg region,
Fig. 5a 2 ) has been destroyed by the heat. Thus, reactions which in
Gryllus and Platycnemis occur after the energids have approached the
surface, may, in Tenebrio, take place in the interior of the yolk system.
The influence of the posterior pole region was demonstrated positively
in Euscelis, where anterior isolates formed complete embryos, instead
of developing almost extraembryonically, provided they had been
furnished with posterior pole material (Sander, 1960; cf. Section VII B).
According to topohistochemical investigations (Bier, unpublished
data) the oosome in the ant Camponotus consists of material containing
RNA and highly refractive granules, possibly protein. During oosome
dissolution these refractive bodies migrate anteriorly, sometimes carrying remnants of their basophilic covering, and disappear shortly before
reaching the middle of the egg. Since in Reith's (1931) experiments
periplasm differentiation and, consequently, position of the germ anläge
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
posterior cell movements leading to germ anläge formation and anatropsis (Fig. 6d-f, curve IV); the cause for these morphogenetic movements
must therefore lie in the yolk plasmodium.
A factor region near the posterior pole has been demonstrated in
other insects as well (e.g. Camponotus; Reith, 1931, 1932,: Tenebrio;
Ewest, 1937) and in some cases (Tachycines, Notonecta; Krause, 1938b:
Euscelis; Sander, 1959) is thought to be homologous to the AC of Pia -
tycnemis. Mahr (1960b) demonstrated that the position of the AC differs
slightly in different egg clusters of Gryllus. By a refined technique of
ligation, he was able to demonstrate also a slight spread of effects of the
centre between the 2- and 512-nuclei stage. Removal of the AC in Gryllus
is followed by extraembryonic development (Fig. 7f-h) as in Platyznemis. The egg of Tenebrio passes a critical period during cleavages VI
and VII (Ewest, 1937). Posterior pole cautery before the 64-nuclei stage
even prevents formation of the energid spheroid and of the blastoderm;
those energids which have not become inactivated by heat become primary vitellophags in the interior part of the egg, whereas in the dense
marginal plasm of the prospective germ disc, plasma islands appear with
a distribution similar to that of secondary vitellophags in normal development. The suppression of spheroid and blastoderm formation may be
ascribed to destruction of an AC not yet functioning; however, it may
equally well be due to a toxic substance created by early cautery. Operation after the 64-nuclei stage is followed by formation of an energid
spheroid, blastoderm, primary and secondary vitellophags, yolk cleavage, and even yolk contraction, but no germ anläge appears. From
this, one might conclude that an AC has become effective after the 64nuclei stage, but some differentiation factor necessary for germ anläge
formation and even for predisposition of the germ anläge in the energid
spheroid (normally the energids accumulate in the embryonic egg region,
Fig. 5a 2 ) has been destroyed by the heat. Thus, reactions which in
Gryllus and Platycnemis occur after the energids have approached the
surface, may, in Tenebrio, take place in the interior of the yolk system.
The influence of the posterior pole region was demonstrated positively
in Euscelis, where anterior isolates formed complete embryos, instead
of developing almost extraembryonically, provided they had been
furnished with posterior pole material (Sander, 1960; cf. Section VII B).
According to topohistochemical investigations (Bier, unpublished
data) the oosome in the ant Camponotus consists of material containing
RNA and highly refractive granules, possibly protein. During oosome
dissolution these refractive bodies migrate anteriorly, sometimes carrying remnants of their basophilic covering, and disappear shortly before
reaching the middle of the egg. Since in Reith's (1931) experiments
periplasm differentiation and, consequently, position of the germ anläge