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 238 EMBRYOLOGY OF INSECTS AND MYRIAPODS splm a pair of deep medially directed invaginations arises just behind the mandi- bles which fuse with the T-shaped invaginations to form the tentorium. The dorsal tentorial arms arise afterward as outgrowths from the anterior tentorial arms. The mandibular apodemes arise at the 90-hour stage as a pair of deep invagina- tions near the middle 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 238 EMBRYOLOGY OF INSECTS AND MYRIAPODS splm a pair of deep medially directed invaginations arises just behind the mandi- bles which fuse with the T-shaped invaginations to form the tentorium. The dorsal tentorial arms arise afterward as outgrowths from the anterior tentorial arms. The mandibular apodemes arise at the 90-hour stage as a pair of deep invagina- tions near the middle of the inner side of the mandibular base. The lower flexor mandibular muscles become attached to them. In- vaginations appearing soon after blastokinesis and proceeding back- ward from either side of the base of the newly formed hypopharynx on the ventral side form the salivary glands. Already one day after blastokinesis the two invagi- nations approach each other and finally fuse near their mouths to form the common salivary duct. Just after the completion of blastokinesis the median area of the floor of the buccal cavity immediately in front of the labium becomes thickened to form the hypopharynx. This area arises by fusion of the sternites of the three jaw segments. As the mandibles and maxillae move closer to the mouth, the hypopharynx becomes closely associated with them. In the 112-hour embryo the dorsomedian walls of the coelomic sacs of all segments of thorax and abdomen begin to grow medially beneath and along the provisional dorsal closure (Fig. 160). Two lateral bands of splanchnic mesoderm are thus formed. This splanchnic mesoderm is two or more cells deep, the outer, or dorsal, layer in contact with the provisional dorsal closure, and the inner thin layer with a single layer of nuclei at right angles to the longitudinal axis of the embryo. The outer layer gives rise to the longitudinal and circular muscles of the mid-gut; the inner layer soon after blastokinesis sepa
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