Embryology of insects and myriapods; Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching embryologyofinse00joha Year: 1941 EPHEMERIDA, ODONATA, PLECOPTERA, ET AL. 193 indicating that maturation and fertilization occur previous to that time (Fig. 113A). A short time later, cleavage nuclei are on their way to the Fig. 114:.—Libellula. (am) Amnion, {bid) Blastoderm, {gb) Germ band, {hi) Head lobe, {y) Yolk. periphery (Fig, 1135). In an egg six hours old two nuclei and three cytoplasmic masses appear, indica
Embryology of insects and myriapods; Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching embryologyofinse00joha Year: 1941 EPHEMERIDA, ODONATA, PLECOPTERA, ET AL. 193 indicating that maturation and fertilization occur previous to that time (Fig. 113A). A short time later, cleavage nuclei are on their way to the Fig. 114:.—Libellula. (am) Amnion, {bid) Blastoderm, {gb) Germ band, {hi) Head lobe, {y) Yolk. periphery (Fig, 1135). In an egg six hours old two nuclei and three cytoplasmic masses appear, indicating this to be probably the eight-cell stage. The nuclei, as they migrate from the center of the egg toward the periphery, are surrounded by small amounts of cytoplasm. The yolk mass seems to be closely packed so that each nucleus is tightly wedged in by blocks of yolk with cytoplasm streaming out in the interstices between blocks. When the nuclei reach the surface and enter the cortical layer, they are spaced far apart (Figs. 113C, 114A), and the cytoplasm between them appears thread-like in cross section (Fig. 116, pr). Figure 115 shows a section of the blastoderm after the cleavage nuclei have multi- plied for some time and the yolk in the vicinity has been liquefied. After the blastoderm is completed, a strip on the ventral side of the egg thickens, forming the germ band, the remainder of the blastoderm becom- ing very thin. A depression then appears near the posterior end of the
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