288
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
patterns originate in the ooplasm may be ascertained once ultrastructure
of the egg has been investigated thoroughly by the electron microscope.
Plasma streaming in well-defined directions, however, must be involved
in the regional increase of primary or secondary periplasm, or in the
formation of plasma islands in pseudo-cleavage.
A. Germ Anlage Formation
Subsequent to blastoderm formation, blastemas are involved in
morphogenetic movements. Blastemic reaction systems may take part
in the segregation of germ anläge and mesoderm, but these are outside
the scope of this article. On the other hand, it is well established that, at
least in the case of 'yolk-rich' eggs of hemimetabolous insects, morphogenetic movements of the yolk plasmodium play a decisive role in causing movements of the blastoderm cells and of the germ disc as a whole.
By U.V.-irradiation of Gryllus eggs during the blastoderm stage, Sauer
(1961a,b), besides observing a surprising capacity for regulation, was
able to demonstrate that the ability of the yolk plasmodium to contract
strongly is limited to the time and egg region typical for germ anläge
formation, and occurs only laterally and not in dorsoventral direction.
In the experiments, ventral unification of remnants of the embryonic
blastoderm was strongly retarded, but the longitudinal movement
caused by streaming of marginal endoplasm (see Section VI B) remained
undisturbed. The primitive groove, due to regulation, may appear at
atypical places, preferably close to the depression caused by irradiationinduced yolk contraction.
Apart from the question as to whether or not the yolk plasmodium in
other insects gains its contractility by the same reaction sequence as in
Platycnemis and Gryllus, one may enquire where in similar insect eggs
the yolk contractions start, and what conditions distinguish this initial
place of blastemic differentiation (DC). The general pattern of lateral
increase of blastoderm thickness with subsequent ventral confluence of
the lateral ectoderm plates to form one ventral germ anläge {Platycnemis, Gryllus, Euscelis) may be modified in accordance with two other
trends of germ anläge formation; either blastoderm cells may assemble
dorsally before the lateral plates appear (e.g. T achy eines), or the germ
disc appears directly on the ventral side (e.g., Eutermes, Carausius
Sialis, Panorpa, Tenebrio, Plodia): I t is interesting to note whether the
material in which differentiation starts, as testified by an increase in
thickness, is used subsequently for head, thorax, or terminal body
regions. According to this, the egg plasmodium may contain a procephalic, gnathic, thoracic, or abdominal differentiation centre.
Platycnemis (Fig. 6) is distinguished by a prothoracic contraction
centre of the yolk plasmodium; this dynamic DC ('morphologisches
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
patterns originate in the ooplasm may be ascertained once ultrastructure
of the egg has been investigated thoroughly by the electron microscope.
Plasma streaming in well-defined directions, however, must be involved
in the regional increase of primary or secondary periplasm, or in the
formation of plasma islands in pseudo-cleavage.
A. Germ Anlage Formation
Subsequent to blastoderm formation, blastemas are involved in
morphogenetic movements. Blastemic reaction systems may take part
in the segregation of germ anläge and mesoderm, but these are outside
the scope of this article. On the other hand, it is well established that, at
least in the case of 'yolk-rich' eggs of hemimetabolous insects, morphogenetic movements of the yolk plasmodium play a decisive role in causing movements of the blastoderm cells and of the germ disc as a whole.
By U.V.-irradiation of Gryllus eggs during the blastoderm stage, Sauer
(1961a,b), besides observing a surprising capacity for regulation, was
able to demonstrate that the ability of the yolk plasmodium to contract
strongly is limited to the time and egg region typical for germ anläge
formation, and occurs only laterally and not in dorsoventral direction.
In the experiments, ventral unification of remnants of the embryonic
blastoderm was strongly retarded, but the longitudinal movement
caused by streaming of marginal endoplasm (see Section VI B) remained
undisturbed. The primitive groove, due to regulation, may appear at
atypical places, preferably close to the depression caused by irradiationinduced yolk contraction.
Apart from the question as to whether or not the yolk plasmodium in
other insects gains its contractility by the same reaction sequence as in
Platycnemis and Gryllus, one may enquire where in similar insect eggs
the yolk contractions start, and what conditions distinguish this initial
place of blastemic differentiation (DC). The general pattern of lateral
increase of blastoderm thickness with subsequent ventral confluence of
the lateral ectoderm plates to form one ventral germ anläge {Platycnemis, Gryllus, Euscelis) may be modified in accordance with two other
trends of germ anläge formation; either blastoderm cells may assemble
dorsally before the lateral plates appear (e.g. T achy eines), or the germ
disc appears directly on the ventral side (e.g., Eutermes, Carausius
Sialis, Panorpa, Tenebrio, Plodia): I t is interesting to note whether the
material in which differentiation starts, as testified by an increase in
thickness, is used subsequently for head, thorax, or terminal body
regions. According to this, the egg plasmodium may contain a procephalic, gnathic, thoracic, or abdominal differentiation centre.
Platycnemis (Fig. 6) is distinguished by a prothoracic contraction
centre of the yolk plasmodium; this dynamic DC ('morphologisches