. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 239 The epineural sinus, which appears early in embryonic development between the germ band and the yolk, is bounded dorsally by the provi- sional dorsal closure in Locusta (Fig. 152), in Stenobothrus, and probably in some other primitive insects, although in most of the pterygotes it is open dorsally. With the growth of the embryo the sinus becomes enlarged and forms the defi
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 239 The epineural sinus, which appears early in embryonic development between the germ band and the yolk, is bounded dorsally by the provi- sional dorsal closure in Locusta (Fig. 152), in Stenobothrus, and probably in some other primitive insects, although in most of the pterygotes it is open dorsally. With the growth of the embryo the sinus becomes enlarged and forms the definitive body cavity, the haemocoele. The heart, or dorsal vessel, is formed from the cardioblasts, differ- entiated in the 112-hour stage as two strings of single large rounded cells lying on the dorsolateral border of the myoblast and extending through the thorax and abdomen. With further development the cardioblasts move toward the middorsal Hue and come to lie beneath the first lateral blood sinus. At the same time they become crescent-shaped, with the concave surface facing upward. The middorsal sinus in the posterior h muG. Fig. 162.—Locusta. Cross section of heart (h) five days after blastokinesis. (cbl) Cardio- blasts. (/) Fat. {mus) Muscle, {pc) Pericardial cells, (pd) Pericardial diaphragm. region of the abdomen at the time of blastokinesis is bounded dorsally by the epidermis, ventrally by the provisional mesoderm wall of the mid- gut, and laterally by somatic mesoderm. The cardioblasts lie dorso- laterally close to the epidermis. Inside the sinus a few blood cells may be seen (Fig. 159). The dorsal portion of the somatic mesoderm mass (Figs. 159, 162) completely separates from the ventral part, becomes membranous, and acquires a connection with the body wall by means of fan-shaped processes. The dorsal membrane finally gives rise to intersegmentally placed suspensory muscles of the heart, and the ventral membrane to the pericardial diaphragm (Fig. 159). With the fus
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