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 184 EMBRYOLOGY OF INSECTS AND MYRIAPODS Numerous scattered entoderm cells (ent) that are derived from the ento- derm cells of the ring wall (Fig. 102, ent) and that were pushed toward the yolk may now be observed on the inside of the thin blastoderm wall (Fig. 103, ent). As development proceeds, the upper, nonembryonic part of the blastoderm becomes thin, while in the lower or embryonic
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 184 EMBRYOLOGY OF INSECTS AND MYRIAPODS Numerous scattered entoderm cells (ent) that are derived from the ento- derm cells of the ring wall (Fig. 102, ent) and that were pushed toward the yolk may now be observed on the inside of the thin blastoderm wall (Fig. 103, ent). As development proceeds, the upper, nonembryonic part of the blastoderm becomes thin, while in the lower or embryonic part the outer layer of ectodermal cells becomes columnar and those of the inner layer flat (Fig. 104). The germ band is broadest at the head end where the head lobes are prominent, narrower in the middle section, and again somewhat wider at the posterior end (Fig. 105). At this stage the thin lateral parts of the original blastoderm may be designated as the 'amnio- do mmm'^ J'-> -^?. â .V® Fig. 105.âCampodea. Germ band. Fig. 106.âCampodea. Embryo with dorsal organ (do). serosa.' Meanwhile, the inner-layer mesoderm in the abdomen has divided longitudinally. Segmentation of head and thorax occurs with the appendages (labrum, antennae, mouth parts, and legs) becoming evident. With the segmentation of the anterior part of the abdomen the proctodeal invagination appears. When segmentation of the abdomen is completed, the appendages of the intercalary (premandibular) segment become distinct, and later rudimentary appendages form on the intermediate abdominal segments. The last (tenth) abdominal segment later will be provided with cerci. The entoderm cells (Fig. 104, ent), which at an early stage are found rather uniformly dispersed on the inner surface, later migrate into the yolk where they become distributed. Of their further history Uzel (1898) has given no information. Before the segmentation of the abdomen has been completed, a dorsal migration of some cells from t
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