The erection is necessary in order to achieve the penetration of the vagina.

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The erection is necessary in order to achieve the penetration of the vagina. In response to mechanical or psychological, i.e. stimulation, the erection is achieved through a nervous mechanism which causes a rush of blood into the organ and at the same time greatly restricts its flow, thus causing rigid distension. Like the size the shape also varies from man to man. Penis is the male organ which releases the semen into vagina. The foremost end of the penis is called glans penis.  King Size Male Enhancement It is slightly thicker than the rest of the shaft. In the flaccid state, the glans is partly or wholly covered by a loose layer of the skin, in the uncircumcised men, called the prepuce or foreskin. This is retracted for the purpose of cleaning and it becomes naturally retracted after entry in coitus.  http://www.healthcaresdiscussion.com/king-size-male-enhancement/