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 SIPHONAPTERA AND DIPT ERA 379 The rudiment by this time has become cleft at the free end into two branches which are in contact with a ribbon of mesoderm that is destined to form the muscle layers of the mid-gut. Later the mesenteron rudi- ments elongate, and the stomodaeal invagination deepens (Fig. ). A B Fig. 335.—Calliphora vomitoria. Section A is taken at the level of k of
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 SIPHONAPTERA AND DIPT ERA 379 The rudiment by this time has become cleft at the free end into two branches which are in contact with a ribbon of mesoderm that is destined to form the muscle layers of the mid-gut. Later the mesenteron rudi- ments elongate, and the stomodaeal invagination deepens (Fig. ). A B Fig. 335.—Calliphora vomitoria. Section A is taken at the level of k of Fig. 329; B at the level of u. (ect) Ectoderm, {ent) Entoderm, {mes) Mesoderm. Posteriorly at this time the posterior mesenteron rudiment is divided api- cally into two branches in the same manner as the anterior rudiment. With the shortening of the embryo the proctodaeal opening comes to lie near the posterior end of the egg, with the result that the posterior mesen- teron rudiment has its apex directed anteriorly (Fig. 3325). Subsequently the elongation of the paired branches, or ribbons, of the two rudiments meet and then widen until their edges fuse, forming the mid-gut epithelium, a tube enclosing the yolk except for a small portion of the yolk which remains in the head region. The yolk cells take no part in the formation of the mid- gut epithelium. Escherich (1900) and Noack (1901) both maintain that the anterior and posterior mid-gut rudiments represent the entoderm. Escherich, in common with a number of other investigators, considered the longitudinal ventral furrow as a much elongated gastrula furrow at the extremities still preserving its original condition, the invaginated part formed exclu- sively of entoderm (Fig. 335^,en^. At the anterior end but slightly farther back lateral mesodermic diverticula appear (Fig. Sd5B,mes), and a
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