T H E E A R L Y E M B R Y O G E N E S I S OF I N S E C T S
287
very important, is not studied so easily since, unless it causes changes in
appearance of the nucleus (e.g., endomitotic growth of prospective
germ band cells turned into supernumerary vitellophags by constriction
of Calliphora eggs, see Section IV B) or prevents such changes (e.g. chromosome elimination in Wachtliella, see Section III B), it may become manifest only after a chain of further reactions. Cytoplasmic influences may
cause meiosis and determine the fate of the daughter nuclei arising from
it (von Borstel, 1955); they may also mediate in inactivation of supernumerary sperm, and are likely to induce the change of the sperm head
into the male pronucleus. Migration of the" female*[nucleus, at least in
eggs developing parthenogenetically (Seiler and Schäffer, 1960), must
also be caused by specific factors in the ooplasm although these may not
act upon the nucleus itself but rather upon the plasm that probably
carries it. A more complicated but undeniable influence of the ooplasm
upon the nuclei is demonstrated by those experiments in which equipotent cleavage nuclei (see Section IV A), under the influence of different
ooplasmic factors, take part in the formation of quite different tissues
(e.g. Euscelis, Section VII B). Interactions of this sort are a postulate
for any type of epigenesis.
V I . Morphogenetic Movements
Interaction between egg components as a principle of determination
is not limited to the submicroscopical level; quite a number of dynamic
processes may be observed with the light microscope as morphogenetic
movements. Concerning the releasers of these movements, as little is
known about these as about activation of control centres and about
interactions between control genes and control substances. The relations
known to exist between formative movements and ooplasm structures,
reaction times, and reaction places will be reviewed in this section.
Analysis of morphogenetic movements as carried on by Vogt (1923)
and Seidel (1934) ('Morphodynamik' of Lehmann, 1958) starts with the
quest for initial regions of morphogenesis and of their material prerequisites. The formation and regional increase of periplasm, movements
of cleavage energids, formation of germ anläge and mesoderm, embryonic envelopment and anatrepsis are outstanding among the kinetic
phenomena. Observational data concerning nuclear movements in
cleavage and centrifugal movement of spheroid energids are discussed
by Johannsen and Butt (1941, p. 146). We have quoted experiments
(Section IV A) which prove that plasma streaming is not the primary
factor in these processes; it is rather that mitotic movement is being
furthered or hampered in certain directions by ooplasmic gradients of
the cleavage and differentiation centres. How such gradients and topical
287
very important, is not studied so easily since, unless it causes changes in
appearance of the nucleus (e.g., endomitotic growth of prospective
germ band cells turned into supernumerary vitellophags by constriction
of Calliphora eggs, see Section IV B) or prevents such changes (e.g. chromosome elimination in Wachtliella, see Section III B), it may become manifest only after a chain of further reactions. Cytoplasmic influences may
cause meiosis and determine the fate of the daughter nuclei arising from
it (von Borstel, 1955); they may also mediate in inactivation of supernumerary sperm, and are likely to induce the change of the sperm head
into the male pronucleus. Migration of the" female*[nucleus, at least in
eggs developing parthenogenetically (Seiler and Schäffer, 1960), must
also be caused by specific factors in the ooplasm although these may not
act upon the nucleus itself but rather upon the plasm that probably
carries it. A more complicated but undeniable influence of the ooplasm
upon the nuclei is demonstrated by those experiments in which equipotent cleavage nuclei (see Section IV A), under the influence of different
ooplasmic factors, take part in the formation of quite different tissues
(e.g. Euscelis, Section VII B). Interactions of this sort are a postulate
for any type of epigenesis.
V I . Morphogenetic Movements
Interaction between egg components as a principle of determination
is not limited to the submicroscopical level; quite a number of dynamic
processes may be observed with the light microscope as morphogenetic
movements. Concerning the releasers of these movements, as little is
known about these as about activation of control centres and about
interactions between control genes and control substances. The relations
known to exist between formative movements and ooplasm structures,
reaction times, and reaction places will be reviewed in this section.
Analysis of morphogenetic movements as carried on by Vogt (1923)
and Seidel (1934) ('Morphodynamik' of Lehmann, 1958) starts with the
quest for initial regions of morphogenesis and of their material prerequisites. The formation and regional increase of periplasm, movements
of cleavage energids, formation of germ anläge and mesoderm, embryonic envelopment and anatrepsis are outstanding among the kinetic
phenomena. Observational data concerning nuclear movements in
cleavage and centrifugal movement of spheroid energids are discussed
by Johannsen and Butt (1941, p. 146). We have quoted experiments
(Section IV A) which prove that plasma streaming is not the primary
factor in these processes; it is rather that mitotic movement is being
furthered or hampered in certain directions by ooplasmic gradients of
the cleavage and differentiation centres. How such gradients and topical