. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 223 [leriphery. At about 10 hours, after several divisions, the eggs being maintained at a constant temperature of 33°C., the cleavage cells start migration to the periphery, which they reach by the 18-hour stage. Meanwhile with repeated mitotic divisions there is an anterior migration along the periphery of the egg but not through the yolk. About the twenty-third hour the cel
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. ORTHOPTEROIDEA (PANORTHOPTERA) 223 [leriphery. At about 10 hours, after several divisions, the eggs being maintained at a constant temperature of 33°C., the cleavage cells start migration to the periphery, which they reach by the 18-hour stage. Meanwhile with repeated mitotic divisions there is an anterior migration along the periphery of the egg but not through the yolk. About the twenty-third hour the cells at the posterior end of the egg form a continu- ous layer (Fig. 137) of primary epithelium (blastoderm). Anteriorly the cells are not contiguous until about the twenty-eighth hour (Figs. 138, 139). The cells of the germ disk, or embryonic region (emb), are closely packed together and columnar. Those of the extraembryonic region are elongated tangentially to the egg Fig. 138.—Locusta. Cross section near posterior end. 28-hour stage, (emb) Embryonic portion of blastoderm, {y) Yolk, (yc) Secondary yolk cell. The cells of the germ-disk epithelium undergo rapid division at about the thirtieth hour, with the result that the epithelium temporarily acquires an irregular two- or even three-layered arrangement of the nuclei in places (Fig. 140). At this time the mid-ventral line of the germ disk near its future cephalic end, a shallow groove, is formed on the outer surface. This groove, which lasts for about four hours or less, is called the "first ventral groove" and, according to Roonwal, is not to be confused with the gastral groove. The yolk cells which lie immediately beneath the germ disk at the thirtieth hour are arranged in a layer (Fig. 140, ycm), forming the yolk- cell membrane. The cell boundaries are not visible, the nuclei being connected by protoplasmic strands forming a continuous membrane. Please note that these images are extracted from scanne
Size: 1907px × 1310px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
