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 366 EMBRYOLOGY OF INSECTS AND MYRIAPODS The entoderm that will form the epithelial lining of the mid-gut will develop from two masses of cells, which form the two ends of the inner layer. These are not connected by a middle entodermal strand. The remainder of the inner layer lying between the entodermal masses will become the mesoderm. This is similar to the development of the entoderm
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 366 EMBRYOLOGY OF INSECTS AND MYRIAPODS The entoderm that will form the epithelial lining of the mid-gut will develop from two masses of cells, which form the two ends of the inner layer. These are not connected by a middle entodermal strand. The remainder of the inner layer lying between the entodermal masses will become the mesoderm. This is similar to the development of the entoderm and mesoderm in Musca, as described by Escherich (1900) and Graber (1889). Segmentation begins at the twenty-fifth hour. This process starts first at the cephalic end, the head segments forming and deepening long ect Fig. 321.—Sciara. Longitudinal section of embryo at 34 hours, {am) Amnion, (ect) Ectoderm, (gc) Germ cells. {U) Inner layer, (y) Yolk. Fig. 322.—Sciara. Cross section of coiled embryo at 34 hours (amnion omitted), (ect) Ectoderm, (gc) Germ cells, (il) Inner layer, (y) Yolk. before the tail shows any signs of metameric formation. At the anterior pole one of the segmental folds continues to deepen and soon can be identified as the stomodaeum. At the thirty-sixth hour, mandibular, maxillary, and labial segments can be distinguished, with the stomodaeum between the mandibles appearing much deeper than the segmental grooves. At the time that segmentation begins, a second longitudinal depres- sion, the neural groove, forms on the ventral side. A ridge of cells pushes inward against the lower layer, separating it into two parts except for the two entodermal cell masses at the ends which are left intact. These terminal masses are the mesenteron rudiments which will later form the mid-gut.
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