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 TRICHOPTERA AND LEPIDOPTERA 337 mx2 outer, or somatic, mesoderm becomes closely united to the ectoderm, extending dorsally to form the outer wall of the sides and the dorsum. Before the folds meet on the middorsal line, the amnion and serosa are ruptured. The yolk or entoderm cells increase very rapidly both in number and in size before the dorsal closure. Before the splanchnic mesoderm
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 TRICHOPTERA AND LEPIDOPTERA 337 mx2 outer, or somatic, mesoderm becomes closely united to the ectoderm, extending dorsally to form the outer wall of the sides and the dorsum. Before the folds meet on the middorsal line, the amnion and serosa are ruptured. The yolk or entoderm cells increase very rapidly both in number and in size before the dorsal closure. Before the splanchnic mesoderm has completely separated the yolk from the body cavity on the ventral side, some of the yolk cells migrate into the body cavity (Fig. 291,i/c) where they arrange themselves irregularly along the sides of the body wall. At first the cells are arranged singly and indefinitely along the outer wall of the body (Fig. 292), but later, by increasing in numbers, they become arranged in distinct groups. These entoderm (yolk) cells are both more distinct and more numerous in the posterior part of the yolk sac, the epithelial lining of the stomach prob- ably being formed first in the neighborhood of the proctodaeum and then extending forward to the stomodaeum. It is certain that the yolk cells (entoderm) do not form a continuous sac until some time after the formation of the mesodermic musculature of the yolk sac Fig. 293.—Neophylax. Lateral view of right side after revolution, (md) Mandible, (mx 2) Labium, (p 1) First thoracic leg. .K4^
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