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
285
which give rise to six different blastoderm types (three forming embryo
and envelopes, the others serving to lodge symbionts); at the same time,
the oosome dissolves. In females prevented from oviposition, the periplasmic differentiation and oosome dissolution may start autonomously
within the ovarioles before meiosis. The differentiation may be initiated
by the breakdown of the nutritive chamber (Bier, unpublished data).
In unfertilized eggs of Gryllus, nuclear fragments are able to attract
the surrounding endoplasm, and a big degenerating nucleus may form a
giant plasma island. Sometimes, however, the nuclear substance of
unfertilized eggs remains completely inactive, whereas the
k reticuloplasm
autonomously collects in the form of regularly distributed, but not migrating, islands (Fig. 7b, IS) without nuclei of Feulgen-positive materials. This pseudo-cleavage (Mahr, 1960a, b, 1961) begins in the cleavage
centre, and it is there that the islands first reach their final density (Fig.
7b) which corresponds to the distribution of normal energids in the 512nuclei stage. Then, if not sooner, pseudo-cleavage comes to an end and
the contents of the egg dissolve without yolk cleavage. Pseudo-cleavage
can also occur if active nuclei have been damaged by ligation after the
first mitosis. Despite ligature the plasma islands make their appearance
(Fig. 7ο χ ), and reach their final density first in the original CC; this
centre, accordingly, does not shift its position by regulative processes.
Pseudo-cleavage is considered proof of a bipolar gradient system culminating in the CC of Gryllus.
In Tachycines exceptions to the synchrony of energid multiplication
(Krause, 1938a) may have resulted from inactive nuclei and pseudocleavage. Plasma islands without nuclei have been observed in other
insects as well (Seiler, 1924; Ewest, 1937; Counce and Ede, 1957; NarbelHofstetter, 1960; Reinhardt, 1960); since, however, in degenerating
Drosophila eggs ultrastructural particles tend to flow together into big
aggregates (Waddington and Okada, 1960), in some cases these islands
may be due to degeneration rather than to a normal developmental
component.
It is noteworthy that in a process related to pseudo-cleavage even the
mitotic apparatus may be formed autonomously. Exposure of Habrobracon eggs to X-rays or nitrogen mustard in lethal doses (von Borstel,
1955) curbs DNA synthesis. Therefore, Feulgen-positive substances
are only rarely met with in the energids which, after a long period of
restraint, enter the axial plasm and finally may number 50-150; mostly
they contain only spindle-type structures or interphase vesicles. As in
Gryllus, all energids behave like vitellophags, and as such may inflate
their 'empty' nuclear vesicles endomitotically 200-fold.
From these observations, it is obvious that normal cleavage in the
insect egg is based on a synergistic principle of development. AutonoK")
A.M. 2
285
which give rise to six different blastoderm types (three forming embryo
and envelopes, the others serving to lodge symbionts); at the same time,
the oosome dissolves. In females prevented from oviposition, the periplasmic differentiation and oosome dissolution may start autonomously
within the ovarioles before meiosis. The differentiation may be initiated
by the breakdown of the nutritive chamber (Bier, unpublished data).
In unfertilized eggs of Gryllus, nuclear fragments are able to attract
the surrounding endoplasm, and a big degenerating nucleus may form a
giant plasma island. Sometimes, however, the nuclear substance of
unfertilized eggs remains completely inactive, whereas the
k reticuloplasm
autonomously collects in the form of regularly distributed, but not migrating, islands (Fig. 7b, IS) without nuclei of Feulgen-positive materials. This pseudo-cleavage (Mahr, 1960a, b, 1961) begins in the cleavage
centre, and it is there that the islands first reach their final density (Fig.
7b) which corresponds to the distribution of normal energids in the 512nuclei stage. Then, if not sooner, pseudo-cleavage comes to an end and
the contents of the egg dissolve without yolk cleavage. Pseudo-cleavage
can also occur if active nuclei have been damaged by ligation after the
first mitosis. Despite ligature the plasma islands make their appearance
(Fig. 7ο χ ), and reach their final density first in the original CC; this
centre, accordingly, does not shift its position by regulative processes.
Pseudo-cleavage is considered proof of a bipolar gradient system culminating in the CC of Gryllus.
In Tachycines exceptions to the synchrony of energid multiplication
(Krause, 1938a) may have resulted from inactive nuclei and pseudocleavage. Plasma islands without nuclei have been observed in other
insects as well (Seiler, 1924; Ewest, 1937; Counce and Ede, 1957; NarbelHofstetter, 1960; Reinhardt, 1960); since, however, in degenerating
Drosophila eggs ultrastructural particles tend to flow together into big
aggregates (Waddington and Okada, 1960), in some cases these islands
may be due to degeneration rather than to a normal developmental
component.
It is noteworthy that in a process related to pseudo-cleavage even the
mitotic apparatus may be formed autonomously. Exposure of Habrobracon eggs to X-rays or nitrogen mustard in lethal doses (von Borstel,
1955) curbs DNA synthesis. Therefore, Feulgen-positive substances
are only rarely met with in the energids which, after a long period of
restraint, enter the axial plasm and finally may number 50-150; mostly
they contain only spindle-type structures or interphase vesicles. As in
Gryllus, all energids behave like vitellophags, and as such may inflate
their 'empty' nuclear vesicles endomitotically 200-fold.
From these observations, it is obvious that normal cleavage in the
insect egg is based on a synergistic principle of development. AutonoK")
A.M. 2