The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . lium becomes reinforced bycells that migrate from the yolk. K. Escherich (1901), after a newresearch on the embryology of the muscid Diptera, claims that thefore and hind endodermal rudiments arise from the blastoderm byinvagination, and are from their origin distinct from the the w-hole it seems likely that the endoderm is represented inpart by the yolk, and in part by those anterior and posterior rudimentswhich usually form the mesenteron, but that m some Hexapodathe whole digestive
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . lium becomes reinforced bycells that migrate from the yolk. K. Escherich (1901), after a newresearch on the embryology of the muscid Diptera, claims that thefore and hind endodermal rudiments arise from the blastoderm byinvagination, and are from their origin distinct from the the w-hole it seems likely that the endoderm is represented inpart by the yolk, and in part by those anterior and posterior rudimentswhich usually form the mesenteron, but that m some Hexapodathe whole digestive tract may be ectodermal. It must be admittedthat some of the later work on insect embr>ology has justified thegrowing scepticism in the universal applicability of the germ-layertheory. Heider has suggested, however, that the apparent originof the mid-gut from the stomodaeum and proctodaeum may beexplained by the presence of a latent endoderm-group in thoseinvaginations. Embryonic Membranes.—A remarkable feature in the embryonicdevelopment of most Hexapoda is the formation of a protective. Ftom Nuubaum in ^nall and Denny, The Cockroach. LovcU Rccvc & Co. Fig. 16.—Cross section of Embryo of German Cockroach (Phyllo of the germ band a double fold in the undifferentiated blastoderm,which grows over the surface of the embryo, so that its inner andouter layers become continuous, forming respectively the amnionand the serosa (fig. 16, A, S). The embryo of a moth, a dragon-flyor a bug is invaginated into the yolk at the head end, the portion ofthe blastoderm necessarily pushed in with it forming the embryo thus becomes transferred to the dorsal face of the egg,but at a later stage it undergoes reversion to its original ventralposition. In some parasitic Hymenoptera there is only a singleembr>onic membrane formed by delamination from the blastoderm,Avhile in a few insects, including the wingless spring-tails, the em-bryonic membranes are vestigial or entirely wanti
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
