If you rub your finger across the body of an earthworm, you may notice little ripples. earthworms were among the first organisms to display
a coelom,
segmentation,
jointed appendages,
an endoskeleton

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

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