It takes place in the Fallopian tubes half-way through the menstrual cycle. The fertilizing agent is the male sperm, or more exactly, the spermatozoon, a single fertilizing cell being all that is needed. To ensure fertilization therefore, an infinitely small quantity of spermatic liquid containing a large number of spermatozoons (tens of millions at a time) is .required. This liquid is produced by the testicles and temporarily stored in a system of reservoirs and canals that finally lead into the urinary tract; other glands are situated along the latter which contribute their own additional secretions to the sperm itself.
The implantation of the egg fertilized by this process takes place at a precise spot in the female reproductive system: it descends into the uterus via a Fallopian tube and lodges in the body of the uterus where it soon literally implants itself by insertion into the thickness of the mucosa and of the muscle, once the placenta has been formed and with the aid of the latter. If the implantation of the fertilized egg takes place, for example, in the Fallopian tubes instead of in the uterus, pregnancy will be interrupted.
Once the embryo begins to be observable to the naked eye, it looks like a small mass of flesh at the centre of which the appearance of a human being is at first indistinguishable. It grows there in progressive stages which are very well known today; they lead to the bone structure, the muscles, the nervous system, the circulation, and the viscerae, etc.
These notions will serve as the terms of reference against which the statements in the Qur'an on reproduction are to be compared.
