. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 386 EMBRYOLOGY OF INSECTS AND MYRIAPODS pren. ter-4; -pl4 p21 Upon completion of the segmentation the lateral segmented mesoderm bands become more widely separated (Fig. 341 A), rendering the one- layered middle ectodermal strip {memhrana ventralis) more conspicuous. Meanwhile the anlagen of the appendages appear. The lateral part of the segment will develop into the tergite, the mesal part into the sternit
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 386 EMBRYOLOGY OF INSECTS AND MYRIAPODS pren. ter-4; -pl4 p21 Upon completion of the segmentation the lateral segmented mesoderm bands become more widely separated (Fig. 341 A), rendering the one- layered middle ectodermal strip {memhrana ventralis) more conspicuous. Meanwhile the anlagen of the appendages appear. The lateral part of the segment will develop into the tergite, the mesal part into the sternite (Fig. S4:lA,ter, ster). The appendages now begin to lengthen; the antennae (ant) become preoral in position; the unpaired labrum (Ir) develops as a lobe on the clypeal margin and overhangs the mouth. A prominence in front of each antenna that is pushed forward by the anterior migration of the antenna also elongates to become the preantenna (Fig. 341A,pren). Bending of the Germ Band.^— When the segmentation of the germ band has been completed and the rudiments of the appendages are well established, the right and left halves of the germ band separate more and more (Fig. 3-41 A) from each other except at the two ex- tremities. Each half bends sharply at about the ninth and tenth seg- ments to such an extent that the anterior and posterior sternal parts face each other (Fig. 342). The memhrana ventralis (vm) stretches, and the head and tail approach each other until they meet (Fig. 3415, side view). The stretching of the memhrana ventralis is accompanied by the formation of a deep transverse furrow through it, cutting deeply into the yolk which finally divides it, except for a dorsal bridge, into two parts. Figure 343 is a diagrammatic representation of a section taken at right angles to the furrow of the memhrana ventralis when the crests of the furrow from each side have met inside, completely dividing the yolk. The halves of the germ band, in contact only at head and tail (
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