. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 262 EMBRYOLOGY OF INSECTS AND MYRIAPODS When the stage of the blastoderm development just described is reached, the maternal symbiotic organism passes into the mycetom plasma. Contrary to the views of Hirschler (1912), Toth states that he has never observed symbionts in the summer eggs of aphids before blasto- derm formation. As already described, the yolk-cell syncitium gradually grows around the mycetom,
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 262 EMBRYOLOGY OF INSECTS AND MYRIAPODS When the stage of the blastoderm development just described is reached, the maternal symbiotic organism passes into the mycetom plasma. Contrary to the views of Hirschler (1912), Toth states that he has never observed symbionts in the summer eggs of aphids before blasto- derm formation. As already described, the yolk-cell syncitium gradually grows around the mycetom, becoming thinner and membranous. From the inner surface of the syncitium, partition walls arise which divide the mycetom syncitium into mycetocytes (Fig. 187). The walls begin devel- opment at the anterior pole of the egg but not until the invasion of the microorganisms (symbionts) is complete and the infection pore is closed (Fig. 187). After the invasion of symbionts into the interior of the blastoderm has begun, the margin around the opening is turned inward. When the mycetom is filled with microorganisms, the egg follicle closes, which prevents more symbionts from entering. Following this the blastoderm also closes. Mean- while the germ band which has formed on one side of the blastoderm backs further into the interior, dragging with it the portion of the blastoderm that is to form the amnion. The germ cells become evident when the invagination of the caudal end of the germ band into the interior is well under way and the invasion of symbionts is nearly completed. Rapid cell division takes place until a mass of cells is formed at the tip of the tail (Fig. 187), the mass being pushed passively inward toward the anterior pole. As development proceeds, the caudal end of the germ band is reflected, the band assuming an S-shaped figure (Figs. 18SC,D,E). About this time the beginning of the body segmentation and the invagination of the stomodaeum are in evidence. The proctodaeal
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