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
265
cells, reaches almost double the number found in the female egg. Distribution of energids is guided by the differently preformed ooplasms
(see Section IV A).
The role of ooplasmic prerequisites is very well recognized in seasonal
dimorphism since, in this type of 'maternal effect', all genetical differences should be excluded. In the ant, Formica polyctena, which shows
seasonal dimorphism of oogenesis, Bier (1954) studied the influence of
egg architecture on allometric growth during postembryonic development (Fig. 1, a-g). Winter ovarioles (d) form big eggsj each with an
oosome rich in RNA and situated somewhat internally (f). The summer
egg (g) is smaller and contains more water; its oosome is much nearer the
surface and is restricted to | of the volume of the winter oosome. Besides
differences in size of the yolk globules and speed of oogenesis, the difference in size of the nutritive chambers (d, e) and of nutritive cell nuclei
(a, b) is most striking. Nurse cell nuclei are the main source of ooplasmic
RNA (Bier, unpublished autoradiographical results) which concentrates
in the oosome and possibly contributes to protein synthesis after the
winter. The small nurse cell nuclei of the summer ovariole (b) do not
produce much RNA and degenerate earlier (e) .The influence of temperature upon oogenesis is clearly evident in the size of nutritive cell
nuclei (Fig. 1; unbroken line = normal annual cycle, broken line =4°C,
dotted line=change from 4° to 27°C). By keeping queens at different
temperatures, eggs of both types can be obtained simultaneously, and
the issuing larvae can be nursed by different numbers of worker ants
under otherwise identical conditions (Fig. 1, bottom). With a medium
number of nurses, larvae from eggs with big oosomes develop into
females, and larvae from eggs with small oosomes develop into workers.
Intercasts (IC) result if larvae from winter eggs are underfed, or if larvae
from summer eggs are fed too well. Caste determination in Formica
polyctena, then, apart from the type of secretion produced by nurses and
from nutritional factors, is based on the ooplasmic predisposition as
summer egg or winter egg. This example shows quantitative and perhaps
also qualitive differences in egg architecture to predispose the fate of cells
in very late stages of development. There is obviously some extranuclear
storage of material containing or constituting growth information.
B. Control Substances
Experimental analysis has provided us with some insight concerning
the factorial tasks of the ooplasm. Some aspects of the much-quoted
pattern of information located in a cortex will be dealt with in
Section VII. A clear-cut example of specific substances in the endoplasm controlling certain phases of development is provided by
f In all figures, the posterior egg pole is orientated towards the bottom.
265
cells, reaches almost double the number found in the female egg. Distribution of energids is guided by the differently preformed ooplasms
(see Section IV A).
The role of ooplasmic prerequisites is very well recognized in seasonal
dimorphism since, in this type of 'maternal effect', all genetical differences should be excluded. In the ant, Formica polyctena, which shows
seasonal dimorphism of oogenesis, Bier (1954) studied the influence of
egg architecture on allometric growth during postembryonic development (Fig. 1, a-g). Winter ovarioles (d) form big eggsj each with an
oosome rich in RNA and situated somewhat internally (f). The summer
egg (g) is smaller and contains more water; its oosome is much nearer the
surface and is restricted to | of the volume of the winter oosome. Besides
differences in size of the yolk globules and speed of oogenesis, the difference in size of the nutritive chambers (d, e) and of nutritive cell nuclei
(a, b) is most striking. Nurse cell nuclei are the main source of ooplasmic
RNA (Bier, unpublished autoradiographical results) which concentrates
in the oosome and possibly contributes to protein synthesis after the
winter. The small nurse cell nuclei of the summer ovariole (b) do not
produce much RNA and degenerate earlier (e) .The influence of temperature upon oogenesis is clearly evident in the size of nutritive cell
nuclei (Fig. 1; unbroken line = normal annual cycle, broken line =4°C,
dotted line=change from 4° to 27°C). By keeping queens at different
temperatures, eggs of both types can be obtained simultaneously, and
the issuing larvae can be nursed by different numbers of worker ants
under otherwise identical conditions (Fig. 1, bottom). With a medium
number of nurses, larvae from eggs with big oosomes develop into
females, and larvae from eggs with small oosomes develop into workers.
Intercasts (IC) result if larvae from winter eggs are underfed, or if larvae
from summer eggs are fed too well. Caste determination in Formica
polyctena, then, apart from the type of secretion produced by nurses and
from nutritional factors, is based on the ooplasmic predisposition as
summer egg or winter egg. This example shows quantitative and perhaps
also qualitive differences in egg architecture to predispose the fate of cells
in very late stages of development. There is obviously some extranuclear
storage of material containing or constituting growth information.
B. Control Substances
Experimental analysis has provided us with some insight concerning
the factorial tasks of the ooplasm. Some aspects of the much-quoted
pattern of information located in a cortex will be dealt with in
Section VII. A clear-cut example of specific substances in the endoplasm controlling certain phases of development is provided by
f In all figures, the posterior egg pole is orientated towards the bottom.