绒毛膜：在爬行类动物，鸟类及哺乳类动物中包含胚胎的外膜，在有胎盘哺乳动物中与胎盘的发育有关。
Chorion: the outer membrane enclosing the embryo in reptiles birds and mammals. in placental mammals it contributes to the development of the placenta.
绒毛膜：在爬行类动物、鸟类及哺乳类动物中包含胚胎的外膜，在有胎盘哺乳动物中与胎盘的发育有关。
Chorion: the outer membrane enclosing the embryo in reptiles birds and mammals. in placental mammals it contributes to the development of the placenta.
绒毛膜：在爬行类动物、鸟类及哺乳类动物中包含胚胎的外膜，在有胎盘哺乳动物中与胎盘的发育有关。
Chorion: the outer membrane enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta.
之后的五千万年内没有任何新奇的事发生，就在这时，胎盘哺乳动物(或者说是那些有后代存活的哺乳动物)突然之间分化为四种所谓的生物总目。
Nothing much then happened for 50m years when, all of a sudden, the placentals (or, at least, those with surviving descendants) split into four so-called superorders.
当哺乳动物捕获这个基因，利用它在胎盘产生一层融合细胞，通过这层细胞母亲能够将营养物质输送给她们的胚胎。
When mammals captured the gene, they used it in the placenta to create a layer of fused cells through which mothers can send nutrients to their embryos.
他说：“化石记录一再证实现代胎盘类哺乳动物的起源是在白垩纪-早第三纪分界点的时候或那之后。
“The fossil record continues to show that the origin of modern placental mammals postdates or is at the Cretaceous-Paleogene boundary, ” he said.
这些部分的特征让古生物学家得以作出这样的结论：这种动物在哺乳动物谱系中，与有胎盘类的关系较与有袋类(如袋鼠)的关系更接近。
These features led the paleontologists to conclude that the animal was closer to living placentals on the mammalian family tree than to pouched marsupials, such as kangaroos.
史密斯博士说这些虱子不会在他的系统树上出现，除非它们转变成寄生在胎盘类哺乳动物身上的物种，而大多数虱子不会经常变换宿主。
These lice would not show up in his tree, Dr. Smith said, unless they had been able to transfer to the placental mammalian species, and most lice do not regularly switch hosts.
绒毛膜尿囊由融合的绒毛膜和尿囊组成的富含血管的胎膜组织，存在于爬行类动物和鸟类的蛋壳附近，并且构成大多数哺乳动物的胎盘。
The highly vascular fetal membrane that consists of the fused chorion and allantois found adjacent to the eggshell in reptiles and birds and constituting the placenta in most mammals.
由融合的绒毛膜和尿囊组成的富含血管的胎膜组织，存在于爬行类动物和鸟类的蛋壳附近，并且构成大多数哺乳动物的胎盘。
The highly vascular fetal membrane that consists of the fused chorion and allantois, found adjacent to the eggshell in reptiles and birds and constituting the placenta in most mammals.
由融合的绒毛膜和尿囊组成的富含血管的胎膜组织，存在于爬行类动物和鸟类的蛋壳附近，并且构成大多数哺乳动物的胎盘。
The highly vascular fetal membrane that consists of the fused chorion and allantois, found adjacent to the eggshell in reptiles and birds and constituting the placenta in most mammals.
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