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
281
contractility only after the AC factor has spread anteriorly. This contractility is said to be one prerequisite for embryonic differentiation of the
blastoderm. The other prerequisite is a pattern of information for metameric differentiation (Fig. 6c) (cf. Section VII C) of the blastoderm,
Nucl. β
64 256
256/512 570+24 VIT t
(21 °C)
A Qe 6
22
33
36
49
64 h
FIG. 6. Reaction sequence leading to germ anläge formation in Platycnemis (Odonata)
(after Seidel, 1926-1936, 1961). Scale: Percentage of egg length (total about 1 mm).
Eggs seen from the left side; e x is ventrolateral view. Equipotent cleavage energids migrate
into AC (curve i") which gives off formative factor (curve II). Subsequently, the yolk
gains increasing translucency beginning from the posterior pole (curve III). Yolk
plasmodium contracts in initial region of germ anläge formation (IV). Embryonic
blastoderm concentrates in posterior direction (dotted lines) so as to form germ anläge
which, tail end first, is drawn into the yolk (anatrepsis, curve V). For abbreviations see
Fig. 3. Further explanations in the text.
which during blastoderm stages is located near the egg surface between
the 25 and 45% levels and can be destroyed by U.V.-irradiation (Seidel,
1961). In this region, which according to the fate map (Fig. 6d) must be
considered a prothoracic differentiation centre (DC), the yolk plasmodium begins to contract one hour after the blastoderm stage shown in
Fig. 6d. If the egg system is reduced by ligation or by belt irradiation,
the yolk plasmodium nevertheless will contract provided sufficient of
the activated DC remains intact. The contraction, however, in this case
may not begin in its predisposed place, but in a place fitted harmoniously to the proportions of the reduced system. In this case, the DC
factor region and the DC initial region no longer coincide, a result quite
typical for a morphogenetical blastema field reduced in size. Destruction
of the blastoderm in the DC region does not suppress the ventral and
281
contractility only after the AC factor has spread anteriorly. This contractility is said to be one prerequisite for embryonic differentiation of the
blastoderm. The other prerequisite is a pattern of information for metameric differentiation (Fig. 6c) (cf. Section VII C) of the blastoderm,
Nucl. β
64 256
256/512 570+24 VIT t
(21 °C)
A Qe 6
22
33
36
49
64 h
FIG. 6. Reaction sequence leading to germ anläge formation in Platycnemis (Odonata)
(after Seidel, 1926-1936, 1961). Scale: Percentage of egg length (total about 1 mm).
Eggs seen from the left side; e x is ventrolateral view. Equipotent cleavage energids migrate
into AC (curve i") which gives off formative factor (curve II). Subsequently, the yolk
gains increasing translucency beginning from the posterior pole (curve III). Yolk
plasmodium contracts in initial region of germ anläge formation (IV). Embryonic
blastoderm concentrates in posterior direction (dotted lines) so as to form germ anläge
which, tail end first, is drawn into the yolk (anatrepsis, curve V). For abbreviations see
Fig. 3. Further explanations in the text.
which during blastoderm stages is located near the egg surface between
the 25 and 45% levels and can be destroyed by U.V.-irradiation (Seidel,
1961). In this region, which according to the fate map (Fig. 6d) must be
considered a prothoracic differentiation centre (DC), the yolk plasmodium begins to contract one hour after the blastoderm stage shown in
Fig. 6d. If the egg system is reduced by ligation or by belt irradiation,
the yolk plasmodium nevertheless will contract provided sufficient of
the activated DC remains intact. The contraction, however, in this case
may not begin in its predisposed place, but in a place fitted harmoniously to the proportions of the reduced system. In this case, the DC
factor region and the DC initial region no longer coincide, a result quite
typical for a morphogenetical blastema field reduced in size. Destruction
of the blastoderm in the DC region does not suppress the ventral and