. The biology of twins (mammals). Twins. 52 THE BIOLOGY OF TWINS Tr-tl the stages shown in Figs. 15 and 17, the diagrammatic Fig. 16 is shown. Here the embryos, which are in an early primitive-streak stage, have migrated down the meridians of the vesicle and have left behind them thin-walled amniotic connecting canals that still anchor the head ends of the em- bryos to the small common amnion {c am) situated at the distal or vege- tative pole of the egg. The posterior end of each em- bryo is now grow- ing rapidly toward the rim of the Trager ring, a junction with which is soon to be establishe
. The biology of twins (mammals). Twins. 52 THE BIOLOGY OF TWINS Tr-tl the stages shown in Figs. 15 and 17, the diagrammatic Fig. 16 is shown. Here the embryos, which are in an early primitive-streak stage, have migrated down the meridians of the vesicle and have left behind them thin-walled amniotic connecting canals that still anchor the head ends of the em- bryos to the small common amnion {c am) situated at the distal or vege- tative pole of the egg. The posterior end of each em- bryo is now grow- ing rapidly toward the rim of the Trager ring, a junction with which is soon to be established. The sectional view shown in Fig. 14 indicates that the heads of embryos II and IV are growing apart, leaving between them a thin sheet of ectoderm. This, together with the median portion of the original amnion, is des- tined to form a vesicle that remains connected by canals with the amnia of the individual em- bryos and is therefore called the common amnion {c am).. 11-^^ Fig. 16.—Armadillo egg showing four embryos in early primitive streak stages. (See stage VIII.) (From Patterson, but inverted in order to be comparable with the other stages.). 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 Newman, Horatio Hackett, b. 1875. Chicago, Ill. , University of Chicago press
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