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 234 EMBRYOLOGY OF INSECTS AND MYRIAPODS meiit of the abdominal somites differs from that of the thorax only in so far as the former are associated with the development of the gonads and the genital ducts. The genital ducts are differentiated in the median walls of the coelomic sacs from the second to the tenth segments but sub- sequently undergo a concentration so as to become restricte
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 234 EMBRYOLOGY OF INSECTS AND MYRIAPODS meiit of the abdominal somites differs from that of the thorax only in so far as the former are associated with the development of the gonads and the genital ducts. The genital ducts are differentiated in the median walls of the coelomic sacs from the second to the tenth segments but sub- sequently undergo a concentration so as to become restricted to the third to the sixth abdominal segments. A greater part of the dorsal portions of the abdominal somites form myoblast plates and the fat body, as in the thorax. The ventral portions of segments three, four, and six to ten form coelomic ampullae which are comparable to the muscle-forming mesoderm of the thoracic legs. In the 52-hour stage, rudiments of the labrum appear as paired swell- ings. Soon, however, the paired nature is no longer evident. The bifid dc coel am procf Fig. 157.—Locusta. Cross section of eleventh abdominal segment, (am) Amnion. {coel) Coelomic cavity, (dc) Provisional dorsal closure, (eps) Epineural sinus, (fid and mes) ectoderm and mesoderm of the proctodaeum {prod). nature of the labrum is of secondary origin. The presence of an inde- pendent pair of coelomic cavities lying in the labrum suggests the appendicular nature of the labrum, although it is not so regarded by most raorphologists. The antennary rudiments arise in the 50-hour stage. At first behind the oral aperture; subsequently, owing to the backward shifting of the latter, they come to lie in front of the mouth. Five days after blastokinesis the segmentation is established for the entire antenna. The intercalary appendages are represented by a thickening of the ecto- derm between the antennae and the mandibles (Fig. 152), but no definite evagination is formed. The thickening is first
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