. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 227 The round concave germ disk composed of long prismatic cells starts forming as a thickening of the primary epithelial cells lying at the pos- terior pole of the egg slightly on the ventral side (Fig. 138). The cells of the extraembryonic primary epithelium are more or less spindle- shaped with large nuclei. The germ disk afterward begins to elongate at the ventroanterior e
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 227 The round concave germ disk composed of long prismatic cells starts forming as a thickening of the primary epithelial cells lying at the pos- terior pole of the egg slightly on the ventral side (Fig. 138). The cells of the extraembryonic primary epithelium are more or less spindle- shaped with large nuclei. The germ disk afterward begins to elongate at the ventroanterior end along the ventral side of the egg. The proto- corm rapidly elongates and at about the 46-hour stage is twice as long as the protocephalon. Four hours later the inner layer begins to show segmentation, especially in the thoracic regions, and the rudiment of the stomodaeum is in evidence. A little later the germ band has divided into four primary segments: a protocephalic and three protocormic. Fig. 145.—Locusta. Longitudinal section of 40-hour embryo, (am) Amnion, (aw. cav) Amniotic cavity, {antr) Anterior end. (c/i) Chorion, {ect) Ectoderm. (t7) Inner layer, (post) Posterior end. {ser) Serosa. ((/) Yolk, (yc) Secondary yolk cell. elements, , four macromeres or macrosomites. Rudiments of three jaw and three thoracic appendages are apparent at the 52-hour stage. Definitive segmentation of the inner layer preceded that of the ectoderm. By the 75-hour stage the entire abdomen becomes externally segmented into 11 segments, thus establishing the definitive body segmentation. Eye pigment first makes its appearance shortly before the beginning of blastokinesis. After the primary segmentation of the inner layer into four macro- meres the definitive segmentation of the inner layer takes place. At the 52-hour stage the inner layer in the head and thorax is divided into segments corresponding to the three gnathal (jaw) segments and the three thoracic segments. The somites are also
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