216
B. L. ASTAUROV
normal progress and completion of their development, with the sole
exception of thermal parthenogenesis, proved to be of the same very
low order of magnitude as in case of spontaneous rudimentary parthenogenesis. This similarity between both kinds of parthenogenesis (natural
and artificial) in respect to their efficiency (or better to say, their
inefficiency) could be explained by the similarity in the cytogenetic
mechanism of parthenogenetic oocyte maturation: in all better-studied
cases of artificial parthenogenesis, both maturation divisions occurred
quite similarly to the cases of normal fertilization and of spontaneous
parthenogenetic activation. This was, for instance, clearly demonstrated
by Frolova's (1935) cytological analysis in many samples of eggs
activated by different means (Koltzoff, 1932a,b) and particularly by the
immersion in iodine + 10% KI solution. The same was found by Bataillon and Tchou-Su (1933) when treating eggs with half-diluted glacial
acetic acid or with C0 2 -saturated seawater. Thus, artificially activated
unfertilized eggs like spontaneously activated ones, generally start their
development after chromosome reduction (in the haploid state), and the
fate of their further development fully depends on the very uncertain
accidental process of restoration of diploidy. Only in extremely rare
cases of an early restoration of diploidy at the very beginning of development, i.e., in cases of automictic fusion of first cleavage nuclei or of
polar body fertilization of the pronucleus, has an artificially activated
egg a chance to successfully terminate its development. As a rule, early
cleavage proceeds with the haploid number of chromosomes and at a
seemingly slackened pace. Fatal consequences of such a haploid cleavage
—tardy and partial restoration of diploidy, frequent cases of excessive
somatic overpolyploidization and of complex mixoploidy—have been revealed in abundance in Frolova's work (1935). The retarded haploid or
mixoploid cleavage gives rise to an insufficient number of blastomeres
scantily populating the yolk only within the micropylar region and
migrating toward the egg surface slowly and asynchronously. As a
morphogenetic consequence, the blastoderm formation is incomplete, the
germ anläge and then the germ band shortened, the separation of the
latter from the egg surface as well as the formation of the amniotic
fold and later of the double membrane with the amnion as an inner
and the serosa as an outer layer are greatly distorted or completely
fail; the resulting dwarf and crumpled embryo usually uncovered by
the egg membranes occupies only a small anterior segment of the ventral
curvature of the egg (presumptive cephalothoracic region). To make a
long story short, the morphogenesis is completely disorganized, and the
embryo doomed to perish.
According to the hypothesis advanced by Bataillon and Tchou-Su
(1933), the immediate causes of severe disturbances that occur in cases
B. L. ASTAUROV
normal progress and completion of their development, with the sole
exception of thermal parthenogenesis, proved to be of the same very
low order of magnitude as in case of spontaneous rudimentary parthenogenesis. This similarity between both kinds of parthenogenesis (natural
and artificial) in respect to their efficiency (or better to say, their
inefficiency) could be explained by the similarity in the cytogenetic
mechanism of parthenogenetic oocyte maturation: in all better-studied
cases of artificial parthenogenesis, both maturation divisions occurred
quite similarly to the cases of normal fertilization and of spontaneous
parthenogenetic activation. This was, for instance, clearly demonstrated
by Frolova's (1935) cytological analysis in many samples of eggs
activated by different means (Koltzoff, 1932a,b) and particularly by the
immersion in iodine + 10% KI solution. The same was found by Bataillon and Tchou-Su (1933) when treating eggs with half-diluted glacial
acetic acid or with C0 2 -saturated seawater. Thus, artificially activated
unfertilized eggs like spontaneously activated ones, generally start their
development after chromosome reduction (in the haploid state), and the
fate of their further development fully depends on the very uncertain
accidental process of restoration of diploidy. Only in extremely rare
cases of an early restoration of diploidy at the very beginning of development, i.e., in cases of automictic fusion of first cleavage nuclei or of
polar body fertilization of the pronucleus, has an artificially activated
egg a chance to successfully terminate its development. As a rule, early
cleavage proceeds with the haploid number of chromosomes and at a
seemingly slackened pace. Fatal consequences of such a haploid cleavage
—tardy and partial restoration of diploidy, frequent cases of excessive
somatic overpolyploidization and of complex mixoploidy—have been revealed in abundance in Frolova's work (1935). The retarded haploid or
mixoploid cleavage gives rise to an insufficient number of blastomeres
scantily populating the yolk only within the micropylar region and
migrating toward the egg surface slowly and asynchronously. As a
morphogenetic consequence, the blastoderm formation is incomplete, the
germ anläge and then the germ band shortened, the separation of the
latter from the egg surface as well as the formation of the amniotic
fold and later of the double membrane with the amnion as an inner
and the serosa as an outer layer are greatly distorted or completely
fail; the resulting dwarf and crumpled embryo usually uncovered by
the egg membranes occupies only a small anterior segment of the ventral
curvature of the egg (presumptive cephalothoracic region). To make a
long story short, the morphogenesis is completely disorganized, and the
embryo doomed to perish.
According to the hypothesis advanced by Bataillon and Tchou-Su
(1933), the immediate causes of severe disturbances that occur in cases