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 ORTHOPTEROIDEA {PANORTHOPTERA) 215 The muscles of the mid-gut are formed from the splanchnic (visceral) layer of the coelomic sacs. Blood cells arise from the median part of the mesodermal layer which originally connected the right and left halves. The fat body arises from a part of the lateroventral wall of the sacs, at first only an inconspicuous mass but later filling a considerable
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 ORTHOPTEROIDEA {PANORTHOPTERA) 215 The muscles of the mid-gut are formed from the splanchnic (visceral) layer of the coelomic sacs. Blood cells arise from the median part of the mesodermal layer which originally connected the right and left halves. The fat body arises from a part of the lateroventral wall of the sacs, at first only an inconspicuous mass but later filling a considerable space in the defini- tive body cavity. As has been described for other Orthoptera, the pericardial septum develops from the dorsad-growing part of the somatic mesoderm, the heart from the crescent-shaped cardioblasts (mesoderm derivatives at the dorsal junction of somatic and splanchnic layers). A delicate ental membrane, similar to that described for Locusta, Pteronarcys, and some other insects but heretofore not recorded for Blattella, has been observed by Dr. L. C. Pettit. Fig. 131. Fig. 132. Fig. 131.—Blattella. Mid-sagittal section of amniotic fold at caudal end. {am) Amnion. (ecO Ectoderm. (iO Inner layer, (ser) Serosa. Fig. 132.—Blattella. Caudal migration of nine-day embryo. The germ cells in the roach are segregated from the median caudal groove during or shortly after segregation of the mesoderm but before mesoderm segmentation and before the formation of the coelomic sacs. Later they migrate forward, are carried dorsad, and come to lie in two strings extending from the second to the seventh segments after having passed through the splanchnic layer into the genital ridges. Here the paired anlagen of the gonads are formed.
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