204
B. L. ASTAUROV
along the lines marked out long ago by Boveri (1889). The general
significance of the method is outlined and the literature reviewed by
Astaurov (1948a). The method also proved to be useful for the discrimination of the relative significance of nuclear versus cytoplasmic injuries
induced by heavy ionizing irradiation (Astaurov, 1947a,b). Another noteworthy example of its application is the induction of complete heterospermic androgenesis in reciprocal crosses of two rather remote forms
of silkworm; adult androgenetic individuals were produced by the cooperation of the domestic B. mori L. nucleus and of the wild B. mandarina Moore cytoplasm, or vice versa (Astaurov and OstriakovaVarshaver, 1957a-c).
A quite independent cycle of investigations was accomplished in the
field of heritable mosaicism and gynandromorphism. Much ingenuity has
been shown by Goldschmidt and Katsuki (1927, 1928, 1931) who revealed
a cytogenetic mechanism unique in the animal kingdom: double fertilization of binucleated eggs in B. mori. Unfortunately this line of work
is not presently being followed.
After this brief survey of the main historical events we may turn to
the subject in more detail.
II. Normal Cytogenetic Mechanism of Gametogenesis
and Early Development of the Silkworm
The normal cytogenetic processes of gametogenesis, maturation, fertilization, and early embryogenesis are represented in the silkworm in the
form typical of the Lepidoptera, and there is not much worth mentioning.
Gametogenesis and meiosis in domesticated B. mori L., as in the wild
species B. mandarina Moore (Japanese island variety) and their hybrids,
were thoroughly investigated and described by Kawaguchi (1928). There
are 28 (haploid number) small round chromosomes in B. mori L. and 27
in the Japanese island variety of B. mandarina, while 28, as in B. mori,
have been found in continental (Ussuri and Shanghai) races of B.
mandarina Moore (Astaurov et al., 1959; Golysheva, 1961).
According to Naville (1937) and Maeda (1939), chiasma formation is
absent during prophase I of female meiosis, but is observed in spermatocytes I. This finding agrees with the total absence of crossing over in the
heterogametic (ZW) female sex in B. mori and with the presence of
crossing over in homogametic males (ZZ). There are no conspicuous
individual morphological differences between different chromosome pairs,
although the sex chromosome pair can probably be cytologically identified by its association with the nucleolus during early oocyte and nurse
cell formation (Kawaguchi, 1938a).
The full-grown oocytes ready for fertilization are in the metaphase I
stage with the spindle situated on the very surface of the egg in the
B. L. ASTAUROV
along the lines marked out long ago by Boveri (1889). The general
significance of the method is outlined and the literature reviewed by
Astaurov (1948a). The method also proved to be useful for the discrimination of the relative significance of nuclear versus cytoplasmic injuries
induced by heavy ionizing irradiation (Astaurov, 1947a,b). Another noteworthy example of its application is the induction of complete heterospermic androgenesis in reciprocal crosses of two rather remote forms
of silkworm; adult androgenetic individuals were produced by the cooperation of the domestic B. mori L. nucleus and of the wild B. mandarina Moore cytoplasm, or vice versa (Astaurov and OstriakovaVarshaver, 1957a-c).
A quite independent cycle of investigations was accomplished in the
field of heritable mosaicism and gynandromorphism. Much ingenuity has
been shown by Goldschmidt and Katsuki (1927, 1928, 1931) who revealed
a cytogenetic mechanism unique in the animal kingdom: double fertilization of binucleated eggs in B. mori. Unfortunately this line of work
is not presently being followed.
After this brief survey of the main historical events we may turn to
the subject in more detail.
II. Normal Cytogenetic Mechanism of Gametogenesis
and Early Development of the Silkworm
The normal cytogenetic processes of gametogenesis, maturation, fertilization, and early embryogenesis are represented in the silkworm in the
form typical of the Lepidoptera, and there is not much worth mentioning.
Gametogenesis and meiosis in domesticated B. mori L., as in the wild
species B. mandarina Moore (Japanese island variety) and their hybrids,
were thoroughly investigated and described by Kawaguchi (1928). There
are 28 (haploid number) small round chromosomes in B. mori L. and 27
in the Japanese island variety of B. mandarina, while 28, as in B. mori,
have been found in continental (Ussuri and Shanghai) races of B.
mandarina Moore (Astaurov et al., 1959; Golysheva, 1961).
According to Naville (1937) and Maeda (1939), chiasma formation is
absent during prophase I of female meiosis, but is observed in spermatocytes I. This finding agrees with the total absence of crossing over in the
heterogametic (ZW) female sex in B. mori and with the presence of
crossing over in homogametic males (ZZ). There are no conspicuous
individual morphological differences between different chromosome pairs,
although the sex chromosome pair can probably be cytologically identified by its association with the nucleolus during early oocyte and nurse
cell formation (Kawaguchi, 1938a).
The full-grown oocytes ready for fertilization are in the metaphase I
stage with the spindle situated on the very surface of the egg in the