. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. Fig. 319.—Sciara. Cross section of germ band, (am) Amnion, (ect) Ectoderm, {il) Inner layer. serosa membrane. Figures 317 and 318 show them just after the serosa is formed. Figure 326 shows them at an advanced stage of development at the eighty-fourth hour. At no time does the serosa form simply part of the dorsal body wall. It is completed at an early hour and remains a separate and distinct membrane until
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. Fig. 319.—Sciara. Cross section of germ band, (am) Amnion, (ect) Ectoderm, {il) Inner layer. serosa membrane. Figures 317 and 318 show them just after the serosa is formed. Figure 326 shows them at an advanced stage of development at the eighty-fourth hour. At no time does the serosa form simply part of the dorsal body wall. It is completed at an early hour and remains a separate and distinct membrane until ruptured in the process of hatching. Soon after the fifteenth hour a depression appears on the ventral side that is caused by a layer of cells, U-shaped in cross section, pushing into the yolk along the mid-longitudinal line (Fig. 318). The depression extends the full length of the embryo, although it does not appear simultaneously throughout its extent (Fig. 321). The lateral portions of the embryo separated by the groove come together and fuse, obliterating the groove and pinching off the U-shaped ridge of cells, which then forms an imperfect gastrular tube, the lumen of which is never very distinct except at the ends (Fig. 318). The lumen soon disappears, leaving a mass of cells lying in an irregular elongate heap along the median line on the inside (Fig. 319). The heap soon flattens out into a plate of columnar cells nearly as wide as the embryo itself (Fig. 322).. am Fig. 320.—Sciara. Cross section of germ band at caudal end. (am) Amnion, (ect) Ectoderm, (gc) Germ cells, (il) Inner Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Johannsen, O. A. (Oskar Augustus), 1870-1961; Butt, Ferdinand Hinckley, 1899-. New York, London, McGraw-Hill Book Company, inc.
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