268
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
second factor is destroyed and no pole cells are formed afterwards. Since
the periplasm is not affected even by very strong centrifugation, the
posterior pole will then be covered by somatic blastoderm. Eggs with
small Somatic' mother germ cells can be reared; the imagines issuing
from them contain rudimentary gonads. Thus the Keimbahn chromosomes appear to be necessary for gonad development. Similar results
were obtained by Bantok (1961) in another cecidomyid, Mayetiola.
Geyer-Duszynska supposes that a product of elimination genes is
formed during early cleavage within the plasma islands of the cleavage
nuclei; this product is thought to be a factor antagonistic to the deeply
staining pole substance, which in Miastor contains RNA and protein
(Nicklas, 1959). The second factor contained in the reticuloplasm of
the posterior pole, the factor causing pole cells to be formed instead of
normal blastoderm, is not yet known. In Drosophila, where pole cell
formation is also suppressed by centrifugation (Imaizumi, 1958b), the
variable fate of the pole cells (Poulson and Waterhouse, 1960; Hathaway
and Selman, 1961) including their monophasic or diphasic entrance into
the egg interior (cf. Counce, 1961) in different species or mutants may be
caused by several ooplasmic factors awaiting histochemical analysis.
The facts related so far have shown that in insects we may expect
three different types of substances acting as factors in the ooplasm:
1. Gene products ('Genwirkstoffe' of Kühn) controlling development
by controlling primary chemical processes. 2. Anticariotypic factors
effecting chromosome elimination, endomitosis, or chromosome modifications (as indicated by in vitro changes in puffing pattern; Kroeger,
1960). 3. Morphogenetic control substances determining the formation
of pole cells, vitellophags or blastoderm cells and predisposing to growth
and other developmental processes, e.g., substances activating a reaction sequence (cf. Section V A) or a chain of inductions. Not all of these
factors may be preformed; some may appear epigenetically due to
ooplasmic or nuclear movements from a primordial locus to the place of
reaction with other ooplasmic or nuclear egg constituents.
C. Control Centres
Egg regions which, on the base of experimental evidence, are recognized as loci of factors decisive for morphogenesis are known as 'factor
regions' (Seidel, 1953; a term roughly corresponding to Seidel's 'physiological centre'). An egg region distinguished as a place of (visible) commencement of a morphogenetic process is called 'initial region' (Krause
and Krause, 1957; corresponding roughly to the 'morphological centre'
of Seidel). Many efforts, not always satisfactory, have been made to
establish the identity of centres of both types found in corresponding
egg regions in different species. In the present connection we wish to
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
second factor is destroyed and no pole cells are formed afterwards. Since
the periplasm is not affected even by very strong centrifugation, the
posterior pole will then be covered by somatic blastoderm. Eggs with
small Somatic' mother germ cells can be reared; the imagines issuing
from them contain rudimentary gonads. Thus the Keimbahn chromosomes appear to be necessary for gonad development. Similar results
were obtained by Bantok (1961) in another cecidomyid, Mayetiola.
Geyer-Duszynska supposes that a product of elimination genes is
formed during early cleavage within the plasma islands of the cleavage
nuclei; this product is thought to be a factor antagonistic to the deeply
staining pole substance, which in Miastor contains RNA and protein
(Nicklas, 1959). The second factor contained in the reticuloplasm of
the posterior pole, the factor causing pole cells to be formed instead of
normal blastoderm, is not yet known. In Drosophila, where pole cell
formation is also suppressed by centrifugation (Imaizumi, 1958b), the
variable fate of the pole cells (Poulson and Waterhouse, 1960; Hathaway
and Selman, 1961) including their monophasic or diphasic entrance into
the egg interior (cf. Counce, 1961) in different species or mutants may be
caused by several ooplasmic factors awaiting histochemical analysis.
The facts related so far have shown that in insects we may expect
three different types of substances acting as factors in the ooplasm:
1. Gene products ('Genwirkstoffe' of Kühn) controlling development
by controlling primary chemical processes. 2. Anticariotypic factors
effecting chromosome elimination, endomitosis, or chromosome modifications (as indicated by in vitro changes in puffing pattern; Kroeger,
1960). 3. Morphogenetic control substances determining the formation
of pole cells, vitellophags or blastoderm cells and predisposing to growth
and other developmental processes, e.g., substances activating a reaction sequence (cf. Section V A) or a chain of inductions. Not all of these
factors may be preformed; some may appear epigenetically due to
ooplasmic or nuclear movements from a primordial locus to the place of
reaction with other ooplasmic or nuclear egg constituents.
C. Control Centres
Egg regions which, on the base of experimental evidence, are recognized as loci of factors decisive for morphogenesis are known as 'factor
regions' (Seidel, 1953; a term roughly corresponding to Seidel's 'physiological centre'). An egg region distinguished as a place of (visible) commencement of a morphogenetic process is called 'initial region' (Krause
and Krause, 1957; corresponding roughly to the 'morphological centre'
of Seidel). Many efforts, not always satisfactory, have been made to
establish the identity of centres of both types found in corresponding
egg regions in different species. In the present connection we wish to