206
B. L. ASTAUROV
jugated partners is seen from the pole. Often they lie in chains. When
starting to divide links of the chain are drawn apart and the tetrads turn
on their axis through 90°; the reductional split is now located in the
plane of the metaphase plate. The elimination chromatin remaining
stationary and occupying the place of the former metaphase plate appears, therefore, to be some substance formed between conjugation
partners at the site of the reductional split, and the first maturation
division is reductional. As will be seen later (Section III,C,2), this statement is in full agreement with the cytogenetic data on artificial parthenogenesis by heat: the sole maturation division in heat-activated unfertilized eggs proceeds without the formation of the elimination plate, so that
it can be cytologically classified as the second maturation division. At the
same time, genetic data concerning parthenogenesis by heat unquestionably prove that this sole maturation division is the equational one.
On the grounds that Lepidoptera have chromosomes with a diffuse
kinetochore, Suomalainen (1953) at first came to the opposite conclusion,
that meiosis in Lepidoptera is postreductional in the female although
prereductional in the male. Recently, however (Suomalainen, 1965) he
reinvestigated the problem of chiasmata formation and bivalent orientation in female meiosis of Lepidoptera and found his former conclusion
inadequate. As far as the author can judge, there are now no contradictions between the Frolova and Suomalainen viewpoints, so that the prereductional character of female meiosis in Lepidoptera may be taken as
generally accepted.
Some aditional data and the literature concerning the promorphology
of the egg, presumptive regions of germ-band and tissue formation, etc.,
are to be found in recent books on silkworm genetics (Yokoyama, 1959;
Tazima, 1964).
III. Alterations of Developmental Cytogenetic
Mechanisms in the Unfertilized Egg
A. Rudimentary Spontaneous (Natural) Parthenogenesis
1. Spontaneous Parthenogenesis in Unfertilized Diploid Oocytes
a. External Phenomena. The eggs deposited by a normal diploid B.
mori female are at first unpigmented, colored pale lemon-yellow or
cream-white. Rarely, they are of a faint orange-yellow color, characteristic of the wild species B. mandanna. Various shades caused by the
blending of different colors of the chorion and of translucent yolk are
under genetic control.
On the third day after oviposition, monovoltine (diapause) eggs if
fertilized begin to gradually change their shades through the scale of
B. L. ASTAUROV
jugated partners is seen from the pole. Often they lie in chains. When
starting to divide links of the chain are drawn apart and the tetrads turn
on their axis through 90°; the reductional split is now located in the
plane of the metaphase plate. The elimination chromatin remaining
stationary and occupying the place of the former metaphase plate appears, therefore, to be some substance formed between conjugation
partners at the site of the reductional split, and the first maturation
division is reductional. As will be seen later (Section III,C,2), this statement is in full agreement with the cytogenetic data on artificial parthenogenesis by heat: the sole maturation division in heat-activated unfertilized eggs proceeds without the formation of the elimination plate, so that
it can be cytologically classified as the second maturation division. At the
same time, genetic data concerning parthenogenesis by heat unquestionably prove that this sole maturation division is the equational one.
On the grounds that Lepidoptera have chromosomes with a diffuse
kinetochore, Suomalainen (1953) at first came to the opposite conclusion,
that meiosis in Lepidoptera is postreductional in the female although
prereductional in the male. Recently, however (Suomalainen, 1965) he
reinvestigated the problem of chiasmata formation and bivalent orientation in female meiosis of Lepidoptera and found his former conclusion
inadequate. As far as the author can judge, there are now no contradictions between the Frolova and Suomalainen viewpoints, so that the prereductional character of female meiosis in Lepidoptera may be taken as
generally accepted.
Some aditional data and the literature concerning the promorphology
of the egg, presumptive regions of germ-band and tissue formation, etc.,
are to be found in recent books on silkworm genetics (Yokoyama, 1959;
Tazima, 1964).
III. Alterations of Developmental Cytogenetic
Mechanisms in the Unfertilized Egg
A. Rudimentary Spontaneous (Natural) Parthenogenesis
1. Spontaneous Parthenogenesis in Unfertilized Diploid Oocytes
a. External Phenomena. The eggs deposited by a normal diploid B.
mori female are at first unpigmented, colored pale lemon-yellow or
cream-white. Rarely, they are of a faint orange-yellow color, characteristic of the wild species B. mandanna. Various shades caused by the
blending of different colors of the chorion and of translucent yolk are
under genetic control.
On the third day after oviposition, monovoltine (diapause) eggs if
fertilized begin to gradually change their shades through the scale of