. Biology; the story of living things. REPRODUCTION AND LIFE CYCLES 125 The first of these new membranes to be considered are the amnion and chorion. They may be best understood by studying their origin. It will be recalled that in telolecithal eggs the endoderm does not succeed at once in growing ventrally to meet, and so to close, the digestive tube. Instead the unclosed tube lies flat upon the surface of the yolk. Both the ectoderm and mesoderm grow laterally over the endoderm dii'ectly over the yolk on the inner layer of the blasto- derm. The mesoderm as a whole divides into three portions
. Biology; the story of living things. REPRODUCTION AND LIFE CYCLES 125 The first of these new membranes to be considered are the amnion and chorion. They may be best understood by studying their origin. It will be recalled that in telolecithal eggs the endoderm does not succeed at once in growing ventrally to meet, and so to close, the digestive tube. Instead the unclosed tube lies flat upon the surface of the yolk. Both the ectoderm and mesoderm grow laterally over the endoderm dii'ectly over the yolk on the inner layer of the blasto- derm. The mesoderm as a whole divides into three portions, the ectoderm .Tnesoderni ...endbcterm. allantoic cavity amnion \ aWantois amniotic- cavitv znhryoy shell niembn '? embryo. â c.^voll-c" chorion!- extra--' embr/onid coelom ">.,viLe!Une mambrana. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hunter, George W. (George William), 1873-1948; Walter, Herbert Eugene, b. 1867; Hunter, George W. (George William), 1902-. New York, Cincinnati [etc. ] American book company
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