272
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
In some other insect eggs, anterior or posterior regions are distinguished by ooplasmic structures in a way similar to the DC in Apis. Does
this indicate that, in these species, the CC or AC reappear as blastemic
field centres comparable to the DC in Apis
2
. In the egg of Plodia inter -
punctella (Pyralidae) a maximum of ooplasm thickness is preformed
near the front end of the presumptive germ disc (Müller, 1938) where
usually the CC is located; but the central region of the germ disc (prothoracic DC) takes the lead in blastemic differentiation. In Tenebrio,
Ewest (1937) observed the maximum of ooplasm thickness to be located
near the hind pole which in other insects is occupied by an AC; in this
way the boat-shaped germ disc is preformed (Fig. 5a). Experiments
(Section V A) indicate that perhaps the blastemic DC is preformed in
this posterior region close to the AC.
D. Types of Egg Architecture
It is possible to homologize the areas of insect eggs and to classify
insect egg types (Krause, 1939a); this implies that control centres
are situated in identical regions where comparable prerequisites are
available and the same processes begin. If we take the distance CC-DC,
which is kept approximately equal in all examples shown in Pig. 4, to
correspond to the size of the preformed head, we find the 'tagmata',
thorax and abdomen to be of quite different sizes in different egg types
as compared with head size. In 'long-germ' eggs the proportions of the
presumptive tagmata correspond rather closely to those of the full
grown embryo; any growth that occurs involves the germ anläge as a
whole (e.g. Apis, Fig. 3; Pimpla, Fig. 4d; Calliphora, Fig. 8). 'Short
germ' eggs, on the other hand, contain small heart-, shield-, or helmetshaped germ discs usually situated near the posterior pole; such a germ
disc gives rise to the body segments by strong proliferative growth (e.g.
Tachycines, Fig. 4a; Tenebrio, Fig. 5a; Panorpa, Fig. 4b). Most insects
can be grouped somewhere in between these two extremes (e.g. Gryllus,
Fig. 7; Platycnemis, Fig. 6; Euscelis, Notonecta, Fig. 4c; Melasoma,
Fig. 5b). In these 'semi-long germs' only the abdominal segments grow
strongly during embryogenesis.
The proliferative segment-forming zone is basophilic [Tachycines),
but does not contain teloblasts as in other Articulata. Whether growth
factors are preformed near the posterior pole in short-germ eggs or
whether they are produced by the cells of the proliferative zone is not yet
known. Proliferative growth can be observed in eggs with or without
blastokinesis, and in eggs of hemimetabolous as well as holometabolous
insects (Fig. 4). But in any case the egg types differ in spatial arrangement of morphogenetic factors. Since this must originate during oogenesis, we may expect different types of oogenesis.
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
In some other insect eggs, anterior or posterior regions are distinguished by ooplasmic structures in a way similar to the DC in Apis. Does
this indicate that, in these species, the CC or AC reappear as blastemic
field centres comparable to the DC in Apis
2
. In the egg of Plodia inter -
punctella (Pyralidae) a maximum of ooplasm thickness is preformed
near the front end of the presumptive germ disc (Müller, 1938) where
usually the CC is located; but the central region of the germ disc (prothoracic DC) takes the lead in blastemic differentiation. In Tenebrio,
Ewest (1937) observed the maximum of ooplasm thickness to be located
near the hind pole which in other insects is occupied by an AC; in this
way the boat-shaped germ disc is preformed (Fig. 5a). Experiments
(Section V A) indicate that perhaps the blastemic DC is preformed in
this posterior region close to the AC.
D. Types of Egg Architecture
It is possible to homologize the areas of insect eggs and to classify
insect egg types (Krause, 1939a); this implies that control centres
are situated in identical regions where comparable prerequisites are
available and the same processes begin. If we take the distance CC-DC,
which is kept approximately equal in all examples shown in Pig. 4, to
correspond to the size of the preformed head, we find the 'tagmata',
thorax and abdomen to be of quite different sizes in different egg types
as compared with head size. In 'long-germ' eggs the proportions of the
presumptive tagmata correspond rather closely to those of the full
grown embryo; any growth that occurs involves the germ anläge as a
whole (e.g. Apis, Fig. 3; Pimpla, Fig. 4d; Calliphora, Fig. 8). 'Short
germ' eggs, on the other hand, contain small heart-, shield-, or helmetshaped germ discs usually situated near the posterior pole; such a germ
disc gives rise to the body segments by strong proliferative growth (e.g.
Tachycines, Fig. 4a; Tenebrio, Fig. 5a; Panorpa, Fig. 4b). Most insects
can be grouped somewhere in between these two extremes (e.g. Gryllus,
Fig. 7; Platycnemis, Fig. 6; Euscelis, Notonecta, Fig. 4c; Melasoma,
Fig. 5b). In these 'semi-long germs' only the abdominal segments grow
strongly during embryogenesis.
The proliferative segment-forming zone is basophilic [Tachycines),
but does not contain teloblasts as in other Articulata. Whether growth
factors are preformed near the posterior pole in short-germ eggs or
whether they are produced by the cells of the proliferative zone is not yet
known. Proliferative growth can be observed in eggs with or without
blastokinesis, and in eggs of hemimetabolous as well as holometabolous
insects (Fig. 4). But in any case the egg types differ in spatial arrangement of morphogenetic factors. Since this must originate during oogenesis, we may expect different types of oogenesis.