Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 FIG. -153.—a, Egg tube of Foificitla. , Nutritive cells ; E , ovum; OE, epithelium of the wall of the egg tubo. b, Me liau part of the egg tube of a Moth. l?z, nutritive cells of the yolk-chamber; Ez, ovum in the germ-chamber; H, connective tissue investment, so-called serosa. c, Egg-tube of Aphisplafanoides with three ovarian chambers (Ez—Ez') and the terminal nutritive chamber with its cells Ni. Dx, yolk cord. Di
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 FIG. -153.—a, Egg tube of Foificitla. , Nutritive cells ; E , ovum; OE, epithelium of the wall of the egg tubo. b, Me liau part of the egg tube of a Moth. l?z, nutritive cells of the yolk-chamber; Ez, ovum in the germ-chamber; H, connective tissue investment, so-called serosa. c, Egg-tube of Aphisplafanoides with three ovarian chambers (Ez—Ez') and the terminal nutritive chamber with its cells Ni. Dx, yolk cord. Diptera (Cccidomyia, Miastor, fig. TOO), which can reproduce them- selves while still in the larval stage, may be explained. The development of the embryo takes place as a rule outside tho body of the mother, and occupies a longer or shorter period of time, according to the temperature and the time of the year. The centro- iccithal segmentation leads to the formation of a superficial blastoderm, which surrounds the ovum, and always consists of a single layer of ceils. A part of this blastoderm, on that side ot the ovum which the later history shows to be ventral, becomes thickened and sharply
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