Shortly after implantation the embryo gastrulates (within 3 days) maternal blood sinuses bathe the inner cell mass myometrial cells cover and seal off the blastocyst the trophoblast forms two distinct layers

The correct answer is the trophoblast forms two distinct layers.

Under usual conditions, fertilization takes place in one of the fallopian tubes, then the fertilized egg starts to produce its path towards the uterus. By about the fifth day of conception, the embryo ultimately reaches the uterus and gets the implant in the uterine lining or endometrium.

During week II of implantation, the trophoblast layer gets involved by combining with the uterine wall, and during this time the layer of trophoblast differentiates and proliferates into two different layers, that is, cytotrophoblast and syncytiotrophoblast.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

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