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 OLIGOENTOMATA AND APTILOTA 189 development of the larvae further than this point, but in some captured specimens only a little larger than the reared ones the mid-gut epithelium had already assumed its definitive form, and he therefore assumed that further proliferation of the clusters of yolk cells gave rise to the mid-gut lining. The definitive lining (digestive epithelium) consists o
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 OLIGOENTOMATA AND APTILOTA 189 development of the larvae further than this point, but in some captured specimens only a little larger than the reared ones the mid-gut epithelium had already assumed its definitive form, and he therefore assumed that further proliferation of the clusters of yolk cells gave rise to the mid-gut lining. The definitive lining (digestive epithelium) consists of rather large cylindrical cells between which at intervals are clusters (nidi) of smaller, closely crowded replacement, or regenerative, cells. As no proliferations of cells at the tips of either stomodaeal or proctodaeal h crypt mus crypt Fig. 112.—Lepisma. Cross section of seventh abdominal segment. (/) Fat. iggl) Seventh abdominal ganglion, (h) Heart, (mus) Muscle, {at) Stigmata, () Yolk nucleus. invaginations take place, Heymons (1897) concludes that in Lepisma the mid-gut epithelium is of entodermal origin. OBSERVATIONS ON THE DEVELOPMENT OF APTERYGOTA IN GENERAL Cleavage in Campodea and Lepisma is superficial; in Isotoma, Anurida, Achorutes, and Macrotoma, as in many arachnids and crustaceans, it is at first total but later becomes superficial. The entoderm in Campodea, according to Uzel, arises from a thick ring of cells at the ventral pole of the egg, the cells later migrating to the inner wall of the blastoderm and thence into the yolk. The yolk cells are the source of the mid-gut epithelium in Lepisma according to Heymons (1897). In Macrotoma and Achorutes cleavage cells migrating back from the
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