Embriologia di insetti e myriapods; embriologia di insetti e myriapods; la storia evolutiva degli insetti, millepiedi e millepedes da uovo desposition [!] alla schiusa embryologyofinse00joha Anno: 1941 330 EMBRIOLOGIA DI INSETTI E MYRIAPODS mge-^'' il tuorlo. L'estensione caudale del rudiment anteriore e la estensione cefalica del rudiment posteriore (Fig. 285, mge) della prossima riunione sulla superficie dorsale del tuorlo circa un terzo della lunghezza dell'uovo dal suo polo cefalico. La striscia epiteliale così formato si estende rapidamente ventrad sopra i lati del tuorlo fino a quando quest'ultimo è COMPL
987 x 2025 px | 16,7 x 34,3 cm | 6,6 x 13,5 inches | 150dpi
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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 330 EMBRYOLOGY OF INSECTS AND MYRIAPODS mge-^'' the yolk. The caudal extension of the anterior rudiment and the cephalic extension of the posterior rudiment (Fig. 285, mge) next meet on the dorsal surface of the yolk about one-third the length of the egg from its cephalic pole. The epithelial strip thus formed extends rapidly ventrad over the sides of the yolk until the latter is completely enclosed, the two margins of the epithelium meeting and uniting along the ventral mid-line of the yolk a short time before hatching (Fig. 2SlC, mge). Both fore- and hind-guts are formed as usual by ectodermal invaginations (Fig. 285). The stomodaeal invagination is, however, not completely ectoder- mal, since its floor is formed by cells belonging to the anterior mesenteron rudiment, which is not covered by ectoderm. The hind-gut is exclu- sively ectodermal. The lumen of the stomodaeum becomes connected with that of the mid-gut shortly before hatching. A proventricular valve is also formed at this time by folding of the stomodaeal or eso- phageal wall. The lumen of the proctodaeum is at no time in con- nection with that of the mid-gut, both the cephalic end of the hind- gut and the caudal end of the mid-gut being blind. The four Malpighian tubules are formed as ectodermal invaginations which make their appearance prior to the formation of the proctodaeum, grouped around the point where the proctodaeum is to appear. Four separate invaginations have not been observed, the pair situated on each side of the mid-line being con- nected by a shallow crescentric groove. The primary yolk cells, which are derived from cleavage cells remain- ing within the yolk, multiply by. mitosis, the mitotic figures being at first mge-j a^