. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. Mar-aiit(.i,iBM-i.)WM(!i RBPRODUCTION. 79 MBS OF the egg mem- OB result from lence in the if an eggHshell tembranefi,and and albumen, nmalian ovum ed by a zona (zona pettuici- Dunded by an- ry delicate cov- ntettine mem- prowth of the rmic veaide ;) is rapid, and, [led with fluid, is thinned and appears, germinal area I made up of ayera of cells 9), the rest of er part of the L b
. A text-book of comparative physiology [microform] : for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. Mar-aiit(.i,iBM-i.)WM(!i RBPRODUCTION. 79 MBS OF the egg mem- OB result from lence in the if an eggHshell tembranefi,and and albumen, nmalian ovum ed by a zona (zona pettuici- Dunded by an- ry delicate cov- ntettine mem- prowth of the rmic veaide ;) is rapid, and, [led with fluid, is thinned and appears, germinal area I made up of ayera of cells 9), the rest of er part of the L being lined [blast and hyp- irhile the low- ih the embryo epiblast of the >t occur every- beneath which »tion of a patch the future pla- much the same transpiring the ! allantois with ig more promi- ,an. an. nent, and extending between the amnion and subsonal mem- brane. The formation of the chorion marks an important step in the development of mammals in which it plays an important functional part. It is the result of the fusion of the allantois, which is highly vascular, with the subional membrane, the villi of which now become themselves vascular and more complex in other respects. An interesting re- semblance to birds has been observed (by Os- bom) in the opossum (Fig. 83). When the allantois is small the blastodermic vesicle (yelk-sac) has vascular villi, which in all prob- ability not only serve the purpose of attach- ing the embryo to the uterine wall but derive nourishment, not as in birds, from the albumen of the ovum, but directly in some way from the uterine wall of the mother. It will be remembered that the opossum ranks low in the mammalian scale, so that this rtisemblanoe is the more significant from an evolutionary point of view. The term chorion is now restricted to those regions of the subional membrane to which either the yelk-sac or the allan- tois is attached. The former zone has been distinguished as the false chorion and the latter as the true
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Keywords: ., bookauthormillswes, bookcentury1800, bookdecade1890, bookyear1890
