260
G E R H A R D K R A U S E AND K L A U S S A N D E R
hand as they provide a good basis for our survey which deals mainly
with selected examples.
The transformation—by continuous creation of sub-units and their
subsequent integration—of the egg cell into the embryof leads to an
increase in hierarchic organization. In insects, reactions at the ooplasmic level may take place for rather a long period as cleavage nuclei and
other cytoorganelles, instead of being separated by cell walls, together
constitute an 'egg plasmodium'. Subsequent formation of a cellular
blastoderm covering the egg surface limits ooplasmic reactions to the
internal 'yolk plasmodium' containing vitellophags. The plasmodial
phase of development finally comes to an end when the yolk plasmodium
is subdivided into separate yolk cells by (secondary) 'yolk cleavage'.
Reactions at the blastemicj level begin in the blastoderm and lead to
formation of germ layers and primary organ rudiments. Cytoplasmic,
intrablastemic and interblastemic reactions govern growth, organotypic
and histotypic differentiation, and movements leading to segregation and
integration of sub-units. Intra-organic and inter-organic developmental
ctions may take place before or after hatching.
Comparative embryology has shown that certain conditions or phenomena of development may be reduced or caenogenetically produced,
accelerated or retarded, preformed in the egg, or postponed until larval
stages. This means that ontogenesis shows no generally valid intrinsic
subdivisions and should therefore be considered as a whole; only practical reasons justify the limitation of our topic indicated by the title.
Blastemic and incretory reaction systems are reserved for treatment in a
second report, in which also phylogenetical alterations of egg organization and of embryogenesis will be discussed.
II. Natural and Experimental Conditions Influencing Development
A. External Factors
Temperature, humidity, and oxygen supply are environmental factors
which have to be kept optimal during experiments. Temperature,
photoperiod, the presence of plant or animal food, and feeding itself may
create, before and during oogenesis, some prerequisites for embryonic
development, egg diapause, and differentiation of morphs (Bier, 1958;
Buckle, 1959; Kittlaus, 1961; Larsen and Bodenstein, 1959; Paschke,
1959; Wigglesworth, 1960). Genes may act upon the oocyte as external
■f In this paper, the terms 'embryo' and 'embryonic' do not refer to the egg as a whole,
but apply to those parts only which give rise to, or are derived from, the germ band.
I 'Blastema' and 'blastemic' are used here in the general meaning, i.e., to designate an
association of embryonic cells with definable functional state. Weismann's (1863) term
'Keimhautblastem' is replaced by periplasm. The 'blastema' of Patten (1884), the
periplasm with cleavage nuclei (but without cell borders), is referred to as the problastoderm.
G E R H A R D K R A U S E AND K L A U S S A N D E R
hand as they provide a good basis for our survey which deals mainly
with selected examples.
The transformation—by continuous creation of sub-units and their
subsequent integration—of the egg cell into the embryof leads to an
increase in hierarchic organization. In insects, reactions at the ooplasmic level may take place for rather a long period as cleavage nuclei and
other cytoorganelles, instead of being separated by cell walls, together
constitute an 'egg plasmodium'. Subsequent formation of a cellular
blastoderm covering the egg surface limits ooplasmic reactions to the
internal 'yolk plasmodium' containing vitellophags. The plasmodial
phase of development finally comes to an end when the yolk plasmodium
is subdivided into separate yolk cells by (secondary) 'yolk cleavage'.
Reactions at the blastemicj level begin in the blastoderm and lead to
formation of germ layers and primary organ rudiments. Cytoplasmic,
intrablastemic and interblastemic reactions govern growth, organotypic
and histotypic differentiation, and movements leading to segregation and
integration of sub-units. Intra-organic and inter-organic developmental
ctions may take place before or after hatching.
Comparative embryology has shown that certain conditions or phenomena of development may be reduced or caenogenetically produced,
accelerated or retarded, preformed in the egg, or postponed until larval
stages. This means that ontogenesis shows no generally valid intrinsic
subdivisions and should therefore be considered as a whole; only practical reasons justify the limitation of our topic indicated by the title.
Blastemic and incretory reaction systems are reserved for treatment in a
second report, in which also phylogenetical alterations of egg organization and of embryogenesis will be discussed.
II. Natural and Experimental Conditions Influencing Development
A. External Factors
Temperature, humidity, and oxygen supply are environmental factors
which have to be kept optimal during experiments. Temperature,
photoperiod, the presence of plant or animal food, and feeding itself may
create, before and during oogenesis, some prerequisites for embryonic
development, egg diapause, and differentiation of morphs (Bier, 1958;
Buckle, 1959; Kittlaus, 1961; Larsen and Bodenstein, 1959; Paschke,
1959; Wigglesworth, 1960). Genes may act upon the oocyte as external
■f In this paper, the terms 'embryo' and 'embryonic' do not refer to the egg as a whole,
but apply to those parts only which give rise to, or are derived from, the germ band.
I 'Blastema' and 'blastemic' are used here in the general meaning, i.e., to designate an
association of embryonic cells with definable functional state. Weismann's (1863) term
'Keimhautblastem' is replaced by periplasm. The 'blastema' of Patten (1884), the
periplasm with cleavage nuclei (but without cell borders), is referred to as the problastoderm.