THE EARLY EMBRYOGENESIS OF INSECTS
261
factors by producing, during oogenesis, ooplasmic information for
embryonic development. Such maternal effects have been demonstrated
for example in Drosophila in the case of individuals heterozygous for the
particular gene fused; abdominal malformations are shown only if the
mother is of the mutant genotype (Counce, 1956).
External factors are frequently employed in order to damage experimentally parts of the egg. Thermocautery has been refined since Hegner's work (Bock, 1942) and the technique of ligation has been improved
since Seidel's first attempts (Mahr, 1960b). The extraovate method
(Howland and Child, 1935; Krause, 1939b) gave rise to a method of
cutting the germ disc with a glass needle inserted into the egg (Krause
and Krause, 1957). In a kind of autoplastic transplantation, Seidel
(1932) sent the 'wrong' nucleus to the posterior pole region, whereas
Sander (1960) combined posterior pole material with different parts of
the egg. Similar combinations of egg constituents not normally adjacent
have been achieved by means of centrifugation (Geyer-Duszynska,
1959; Yajima, 1960). Ultrasonic treatment has been tested as a method
of creating defects (Counce and Selman, 1955). Krause (1958b) andMahr
(1960b) have eliminated parts of the egg by means of corrosive chemicals. Since unfortunately none but injurious chemicals will enter the egg,
it has not been possible as yet to employ vital staining or radioactive
tracers. Instead of vital marking, small U.V.-defects have been used as a
means of determining the fate of superficial egg materials (Seidel, 1935).
For larger defects, Geigy (1931) and subsequent workers employed the
whole spectrum of an U.V. source, whereas Seidel (1929) was the first
to treat insect eggs with monochromatic U.V.. Total or partial Xirradation was used for analysis of insect embryonic development by
Ulrich (1957), von Borstel (1955) and Bertzbach (1960). Seidel and
Buchholtz (1960) have measured the physiological effects of X-ray
beams of varying diameters down to 35 /x.
B. Internal Factors
Endogenous factors of first rank are comprised in the genetical information contained in the egg nucleus and passed on to the embryonic
cell nuclei. The genome of most species analysed is not nearly as well
known as that of Drosophila. Extensive measurements of egg architecture and kinetic systems as carried out by Seidel's school (Krause,
1938a, b ; Mahr, 1960b) have shown significant differences to exist between different egg clusters. This serves to stress the necessity of using
genetically homogenous stocks for certain investigations. A number of
embryonic lethal factors is known (Counce, 1961; Hadorn, 1955, 1958;
Imaizumi, 1958a; Seeger, 1955; Wright, 1960), but coordination with
experimentally demonstrated development factors governing the same
261
factors by producing, during oogenesis, ooplasmic information for
embryonic development. Such maternal effects have been demonstrated
for example in Drosophila in the case of individuals heterozygous for the
particular gene fused; abdominal malformations are shown only if the
mother is of the mutant genotype (Counce, 1956).
External factors are frequently employed in order to damage experimentally parts of the egg. Thermocautery has been refined since Hegner's work (Bock, 1942) and the technique of ligation has been improved
since Seidel's first attempts (Mahr, 1960b). The extraovate method
(Howland and Child, 1935; Krause, 1939b) gave rise to a method of
cutting the germ disc with a glass needle inserted into the egg (Krause
and Krause, 1957). In a kind of autoplastic transplantation, Seidel
(1932) sent the 'wrong' nucleus to the posterior pole region, whereas
Sander (1960) combined posterior pole material with different parts of
the egg. Similar combinations of egg constituents not normally adjacent
have been achieved by means of centrifugation (Geyer-Duszynska,
1959; Yajima, 1960). Ultrasonic treatment has been tested as a method
of creating defects (Counce and Selman, 1955). Krause (1958b) andMahr
(1960b) have eliminated parts of the egg by means of corrosive chemicals. Since unfortunately none but injurious chemicals will enter the egg,
it has not been possible as yet to employ vital staining or radioactive
tracers. Instead of vital marking, small U.V.-defects have been used as a
means of determining the fate of superficial egg materials (Seidel, 1935).
For larger defects, Geigy (1931) and subsequent workers employed the
whole spectrum of an U.V. source, whereas Seidel (1929) was the first
to treat insect eggs with monochromatic U.V.. Total or partial Xirradation was used for analysis of insect embryonic development by
Ulrich (1957), von Borstel (1955) and Bertzbach (1960). Seidel and
Buchholtz (1960) have measured the physiological effects of X-ray
beams of varying diameters down to 35 /x.
B. Internal Factors
Endogenous factors of first rank are comprised in the genetical information contained in the egg nucleus and passed on to the embryonic
cell nuclei. The genome of most species analysed is not nearly as well
known as that of Drosophila. Extensive measurements of egg architecture and kinetic systems as carried out by Seidel's school (Krause,
1938a, b ; Mahr, 1960b) have shown significant differences to exist between different egg clusters. This serves to stress the necessity of using
genetically homogenous stocks for certain investigations. A number of
embryonic lethal factors is known (Counce, 1961; Hadorn, 1955, 1958;
Imaizumi, 1958a; Seeger, 1955; Wright, 1960), but coordination with
experimentally demonstrated development factors governing the same