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第一节胎儿的发育一、受精和植入受精成熟的卵和精子互相结合的过程叫受精,精卵结合后形成的新细胞叫受精卵。若同时有两个卵受精。则可发育成两个新个体,叫做两卵性双胎,个体的性别和面貌多不相同。受精是在输卵管壶腹部进行的(图1)。受精以后,受精卵便进行细胞分裂,同时向子宫腔方向移动,约经4天到达子宫腔。这时受精卵已分裂成一个细胞团。以后细胞团继续发育,中间出现一个大腔,成为囊胚。囊胚的壁叫滋养层,滋养层内面的细胞群,叫内细胞群。内细胞群中的部分细胞将来发育成胚胎。若一个卵受精以后在囊胚期形成
First, the development of a fetus, fertilization and implantation of fertilized mature eggs and sperm mutual binding process called fertilization, the formation of new cells after sperm-egg called fertilized eggs. If two eggs are fertilized at the same time. You can develop into two new individuals, called the two ovum twins, the individual’s gender and appearance are not the same. Fertilization is performed in the fallopian tube ampulla (Figure 1). After fertilization, fertilized eggs will be cell division, while moving to the direction of the uterine cavity, about 4 days to reach the uterine cavity. At this time the fertilized egg has split into a cell mass. After cell clusters continue to develop in the middle of a large cavity, a blastocyst. The wall of the blastocyst is called the trophoblast, the cell mass on the inside of the trophoblast, called the inner cell mass. Some cells in the inner cell mass develop into embryos in the future. If an egg is fertilized, it forms at the blastocyst stage