THE EARLY EMBRYOGENESIS OF INSECTS
291
by experiments and obversations on Gryllus eggs (Mahr, 1961) (Fig.
7d-h). Damage caused by ligature or acid treatment results in formation
of vacuoles of denatured yolk which may serve as markers of materials
moving within the egg. Before and during germ anläge formation marks
near the surface of the egg (Fig. 7d x : D 2 ) migrate posteriorly, vacuoles
situated interiorly, near the axis (D 1? D 3 ) migrate anteriorly (see d 2 =one
day later). This indicates that marginal endoplasm streams posteriorly
and thereby carries the blastoderm of the germ anläge along. The axial
endoplasm which at the poles is continuous with the marginal layer
contracts in a longitudinal direction thereby pulling marginal material
inwards also at the anterior pole. In isolated egg halves, the axial endoplasm of each part contracts in the same way. At the rear end of the
anterior isolate, the inward movement of marginal plasm is stronger
than it is at the front end of the posterior isolate (arrows in Fig. 7e).
After germ band formation, yolk cleavage takes place and this is followed
by a second contraction of plasmic elements in the yolk causing anatrepsis of the germ band. The dynamic system effecting katatrepsis,
like the system just described, can also function in the absence of the
germ anläge (Mahr, 1961; Krause, 1939b) (Fig. 7f-h). Obviously the
yolk plasmodium is an autonomous dynamic system.
Essentially similar phenomena have been described for other hemimetabolous insects. In T achy eines, Notoneeta, Py villa, and others no
pause has been observed between the backward movement of the germ
anläge and anatrepsis; in some instances yolk cleavage appears to be
closely linked with anatrepsis (Sander, 1956; Baudisch, 1958). Recognition of the different components of the yolk plasmodium dynamics is a
first step towards causal analysis of blastokinesis. The microtopical
factors activating the different movements are as yet unknown.
V I I . Metameric Organization
A. Organ Pattern in the Periplasm
A number of investigations in which destruction of periplasm regions
has been used as a tool (Reith, 1925; Howland and Sonnenblick, 1936;
Smreczynski, 1938; Jura, 1957; Hathaway and Selman, 1961) serve as
a basis for classification of the eggs of Coleoptera and Diptera as typical
mosaic eggs. These eggs are said to contain, even at the beginning of
cleavage, a definitive pattern of organ areas in the periplasm. Other
authors believe that only small topographical changes of anlagen arrangement occur in the cortex (Brauer and Taylor, 1936; Lüscher, 1944;
Brauer, 1949; Haget, 1953). Loss of germ cells following extirpation of
pole plasm, and fate maps of the germ band stage (e.g., Culex; Oelhafen,
1961) are no proof of mosaieism in early cleavage stages. Analysis of
291
by experiments and obversations on Gryllus eggs (Mahr, 1961) (Fig.
7d-h). Damage caused by ligature or acid treatment results in formation
of vacuoles of denatured yolk which may serve as markers of materials
moving within the egg. Before and during germ anläge formation marks
near the surface of the egg (Fig. 7d x : D 2 ) migrate posteriorly, vacuoles
situated interiorly, near the axis (D 1? D 3 ) migrate anteriorly (see d 2 =one
day later). This indicates that marginal endoplasm streams posteriorly
and thereby carries the blastoderm of the germ anläge along. The axial
endoplasm which at the poles is continuous with the marginal layer
contracts in a longitudinal direction thereby pulling marginal material
inwards also at the anterior pole. In isolated egg halves, the axial endoplasm of each part contracts in the same way. At the rear end of the
anterior isolate, the inward movement of marginal plasm is stronger
than it is at the front end of the posterior isolate (arrows in Fig. 7e).
After germ band formation, yolk cleavage takes place and this is followed
by a second contraction of plasmic elements in the yolk causing anatrepsis of the germ band. The dynamic system effecting katatrepsis,
like the system just described, can also function in the absence of the
germ anläge (Mahr, 1961; Krause, 1939b) (Fig. 7f-h). Obviously the
yolk plasmodium is an autonomous dynamic system.
Essentially similar phenomena have been described for other hemimetabolous insects. In T achy eines, Notoneeta, Py villa, and others no
pause has been observed between the backward movement of the germ
anläge and anatrepsis; in some instances yolk cleavage appears to be
closely linked with anatrepsis (Sander, 1956; Baudisch, 1958). Recognition of the different components of the yolk plasmodium dynamics is a
first step towards causal analysis of blastokinesis. The microtopical
factors activating the different movements are as yet unknown.
V I I . Metameric Organization
A. Organ Pattern in the Periplasm
A number of investigations in which destruction of periplasm regions
has been used as a tool (Reith, 1925; Howland and Sonnenblick, 1936;
Smreczynski, 1938; Jura, 1957; Hathaway and Selman, 1961) serve as
a basis for classification of the eggs of Coleoptera and Diptera as typical
mosaic eggs. These eggs are said to contain, even at the beginning of
cleavage, a definitive pattern of organ areas in the periplasm. Other
authors believe that only small topographical changes of anlagen arrangement occur in the cortex (Brauer and Taylor, 1936; Lüscher, 1944;
Brauer, 1949; Haget, 1953). Loss of germ cells following extirpation of
pole plasm, and fate maps of the germ band stage (e.g., Culex; Oelhafen,
1961) are no proof of mosaieism in early cleavage stages. Analysis of